Patent Grant
8228356
1. Field of the Invention
This invention relates generally to driving electronic displays, and more particularly to a display driver circuit and methods for driving a multi-pixel liquid crystal display. Even more particularly, the present invention relates to a driver circuit and method for driving a liquid crystal on silicon display device with a digital backplane.
2. Description of the Background Art
Video data is written into input buffer 110 according to methods well known in the art. In the present embodiment, input buffer 110 stores a single frame of video data for each pixel in pixel array 104. When input buffer 110 receives a command from the system (not shown), input buffer 110 asserts video data for each pixel of a particular row of pixel array 104 onto all 1952 output terminals 114. In the present example, input buffer 110 must be sufficiently large to accommodate four bits of video data for each pixel of pixel array 104. Therefore, input buffer 110 is approximately 8.68 Megabits (i.e., 1952×1112×4 bits) in size. Of course, if the number of bits in the video data increases (e.g., 8-bit video data), then the required capacity of input buffer 110 would necessarily increase proportionately.
The size requirement of input buffer 110 is a significant disadvantage. First, the circuitry of input buffer 110 occupies space on imager 102. As the required memory capacity increases, the chip space required by input buffer 110 also increases, thus hindering the ever present objective of size reduction in integrated circuits. Further, as the memory capacity increases, the number of storage devices increases, thereby increasing the probability of manufacturing defects, which reduces the yield of the manufacturing process and increase the cost of imager 102.
Row decoder 106 receives row addresses from the system (not shown) via a row address bus 116, and responsive to a store command from timing generator 108, row decoder 106 stores the asserted row address. Then, responsive to row decoder 106 receiving a decode instruction from timing generator 108, row decoder 106 decodes the stored row address and enables one of 1112 word-lines 118 corresponding to the decoded row address. Enabling word-line 118 causes data being asserted on data output terminals 114 of input buffer 110 to be latched into the enabled row of pixel cells in pixel array 104.
Select decoder 105 receives block addresses from the system (not shown) via a block address bus 120. Responsive to receiving a store block address command from timing signal generator 108 via timing signal line 112, select decoder 105 stores the asserted block address therein. Then, responsive to timing generator 108 asserting a load block address instruction on timing signal line 112, select decoder 105 decodes the asserted block address and asserts a block update signal on one of 35 block select lines 122 corresponding to the decoded block address. The block update signal on the corresponding block select line 122 causes all of the pixels cells of an associated block of rows of pixel array 104 to assert the previously latched video data onto their associated pixel electrodes (not shown in
Note that the number of rows (i.e., 1112) in pixel array 104 is not evenly divisible into 35 blocks. Accordingly, different blocks will have different numbers of rows. For example, in one embodiment, if 34 of the 35 blocks each contained 32 rows, then the 35th block would contain only 24 rows. Alternatively, if 27 of the 35 blocks contained 32 rows each, then the remaining 8 blocks would contain 31 rows each. In either case, the number of rows updated in each block will vary. This variation in the number of rows assigned to each block will cause the bandwidth and power requirements of display driver 100 and imager 102 to also vary over each frame of display data.
An enable signal on word line 118(r) places transistors 208 and 210 into a conducting state, causing the complementary data asserted on data lines 214(c) and 216(c) to be latched, such that the output of master latch 202 is at the same logic level as data line 214(c). A block select signal on block select line 122(b) places transistor 212 into a conducting state, and causes the data being asserted on the output of master latch 202 to be latched onto the output of slave latch 204 and thus onto pixel electrode 206.
Although the master-slave latch design functions well, it is a disadvantage that each pixel cell requires two storage latches. It is also a disadvantage that separate circuitry is required to write data to the pixel cells and to cause the stored data to be asserted on the pixel electrode.
The ability to rotate the polarization is exploited to modulate the intensity of reflected light as follows. An incident light beam 222 is polarized by a polarizer 224. The polarized beam then passes through liquid crystal layer 218, is reflected off of pixel electrode 206, and passes again through liquid crystal layer 218. During this double pass through liquid crystal layer 218, the beam's polarization is rotated by an amount which depends on the data being asserted on pixel electrode 206 by slave latch 204 (
A common way to drive pixel electrode 206 is via pulse-width-modulation (PWM). In PWM, different gray scale levels (i.e., intensity values) are represented by multi-bit words (i.e., binary numbers). The multi-bit words are converted to a series of pulses, whose time-averaged root-mean-square (RMS) voltage corresponds to the analog voltage necessary to attain the desired gray scale value.
For example, in a 4-bit PWM scheme, the frame time (time in which a gray scale value is written to every pixel) is divided into 15 time intervals. During each interval, a signal (high, e.g., 5V or low, e.g., 0V) is asserted on the pixel storage electrode 106. There are, therefore, 16 (0-15) different gray scale values possible. The actual value displayed depends on the number of “high” pulses asserted during the frame time. The assertion of 0 high pulses corresponds to a gray scale value of 0 (RMS 0V), whereas the assertion of 15 high pulses corresponds to a gray scale value of 15 (RMS 5V). Intermediate numbers of high pulses correspond to intermediate gray scale levels.
(10 of 15 intervals) of the full value (5V), or approximately 4.1V.
Because the liquid crystal cells are susceptible to deterioration due to ionic migration resulting from a DC voltage being applied across them, the above described PWM scheme is modified as shown in
The resolution of the gray scale can be improved by adding additional bits to the binary gray scale value. For example, if 8 bits are used, the frame time is divided into 255 intervals, providing 256 possible gray scale values. In general, for (n) bits, the frame time is divided into (2n−1) intervals, yielding (2n) possible gray scale values. However, as the number of bits and grayscale values increase, the display driver 100 and imager 102 have to operate faster to accommodate additional bit processing.
If the PWM data shown in
What is needed is a system and method that equalizes the transfer bandwidth to the imager and the power requirements needed to update rows of pixels in the imager. What is also needed is a system and method that facilitates processing many display instructions during each frame of display data. What is also needed is a system and method that reduces the number of pulse transitions experienced by the pixels of a display. What is also needed is a system and method that reduces the amount of input memory needed to drive the display. What is also needed is a system and method that reduces visually perceptible aberrations in images generated by a display. What is also needed is a driving circuit and method that can drive pixel arrays with only one storage latch per pixel.
The present invention overcomes the problems associated with the prior art by providing a display driver and method that equalizes the bandwidth between the display driver and the imager over the entire frame. The invention facilitates transferring the same amount of video data during each time interval within a frame by setting the number of time intervals equal to an integer multiple of the number of rows in the display. By equalizing the bandwidth, the power requirements needed to update the pixels in the display are equalized over the frame. The invention also facilitates spreading any unused frame time over the entire frame based on the number of row updates performed during the frame. Furthermore, the invention facilitates driving different portions of an imager's display with different iterations of pixel control circuitry, thereby enabling more intensity values to be defined by each pixel in the display.
The present invention discloses a method for driving a display device having an array of pixels arranged in a plurality of columns and a plurality of rows. The method includes the steps of defining a modulation period for a row of pixels, dividing the modulation period into a plurality of time intervals equal to n times the number of rows in the array, receiving a multi-bit data word that indicates an intensity value to be asserted on a pixel in the row, and updating the signal asserted on the pixel during at least some of the time intervals in the modulation period such that the intensity value defined by the multi-bit data word is displayed by the pixel. Note that n is an integer greater than zero, such as one, two, three, four, and so on.
This method can be applied to all rows by defining a plurality of modulation periods, associating each of the modulation periods with one of the rows in the display, dividing each of the modulation periods into a plurality of time intervals equal to n times the number of rows in the array, receiving a plurality of multi-bit data words that each define an intensity value to be asserted on one of the pixels in the array, and updating the signals asserted on the pixels in each row of the array during a plurality of time intervals in the row's modulation period such that each of the pixels display an intensity value defined by one of the data words. In this particular method, one or more of the modulation periods is temporally offset from the other modulation periods. In particular method, each modulation period is temporally offset by n time intervals from the previous modulation period.
Where n is greater than one, a particular method includes the steps of defining n groups, associating each time interval with one of the groups, and updating the signal on a pixel in a particular row during an equal number of time intervals associated with each group during the pixel's modulation period. A more particular method includes updating the signal on the pixel in (b/n) ones of the time intervals associated with each group during the modulation period, where b equals the number of bits in the multi-bit data word. Where multiple modulation periods are defined for multiple rows, the method further includes updating signals asserted on pixels in the same number of rows during each of the time intervals.
The bit codes of data words used to carry out the various aspects of the present invention are, in some instances, subject to some limitations. According to one aspect of the present invention, the sum of the weighted values of the bits in each multi-bit data word should be equal to n times the number of rows in the array. In addition, the number of bits in the multi-bit data word should be evenly divisible by n. These limitations ensure that an equal number of rows in the display will be updated during each time interval, which ensures 100% bandwidth efficiency between the display driver and the imager(s).
According to another aspect of the present invention where the imager(s) contain (s) iterations of pixel control units and the rows are allocated among (s) sets of rows, then the following additional limitations on the bit code of the data words also apply. First, the sum of the weighted values in each data word should be evenly divisible by s*n, where (s) equals the number of iterations of pixel control circuitry in the imager(s) and (n) is given above. Second, the number of bits in each data word should be evenly divisibly by s*n. Third, an equal number of rows assigned to each of the (s) sets should be updated by each pixel control circuitry unit. This aspect of the invention increases the processing capability of the imagers because each imager can process more data instructions because of the multiple pixel control units.
A particular method according to this aspect of the present invention includes associating each of the rows in the array with one of a plurality of sets of rows and updating the electrical signals asserted on the pixels in a plurality of the rows during each time interval such that each pixel control unit updates only the rows associated with a particular set. For example, for (s) equals two, the even-numbered rows in an imager's display can be associated with a first set, and the odd-numbered rows in the display can be associated with a second set. Accordingly, in an imager with two pixel control units, one pixel control unit updates the even-numbered rows, and the other pixel control unit updates the odd-numbered rows. If both pixel control units update the same number or rows during each time interval, then each pixel control unit operates at 100% efficiency during each time interval.
In many cases, the multi-bit data words of the present methods will be compound data words having both binary-coded bits and thermometer-coded bits. Because intensity values are commonly defined by binary-weighted data words, a particular method of the present invention includes the steps of receiving a binary-weighted data word and converting the binary-weighted data word into a compound data word having at least one binary-coded bit and at least one thermometer-coded bit.
The present invention also provides methods for debiasing the display device and discarding one or more bits of a multi-bit data word before an associated pixel's modulation period is over. For example, where each pixel in the array includes a liquid crystal layer between a pixel electrode and a common electrode, a method for debiasing the pixel array includes the steps of asserting a signal on a pixel relative to the common electrode in a first bias direction during a first group of time intervals in the pixel's modulation period, and asserting the signal on the pixel in a second bias direction during a second group of time intervals. In addition, the method for discarding bits includes the steps of discarding at least one bit of a multi-bit data word prior to the end of the modulation period, and updating the signal on the pixel based on the remaining bits of the multi-bit data word so that the pixel still displays the correct intensity value.
A novel display driver for driving an array of pixels arranged in a plurality of columns and a plurality of rows is also disclosed. The display driver includes a timer that generates a series of time values each associated with one of a plurality of time intervals, a data input terminal set that receives a multi-bit data word indicative of an intensity value to be asserted on the pixel, and control logic that defines a modulation period during which a signal corresponding to the intensity value will be asserted on the pixel and updates the signal during a plurality of the time intervals so that the pixel displays the intensity value. The control logic defines a modulation period with a number of time intervals equal to n times the number of rows in the array, where n is an integer greater than zero.
The display driver drives each row of the array in a similar manner. In a particular embodiment, the data input terminal set receives a plurality of multi-bit data words, each associated with a pixel of the array, and the control logic defines a modulation period for each row in the array and temporally offsets at least one of the modulation periods with respect to every other modulation period. The control logic further updates the signals asserted on pixels in each row during at least some of time intervals in the row's respective modulation period such that an intensity value is asserted on each pixel. Note that each modulation period defined by the control logic contains a number of time intervals equal to n times the number of rows in the array. In a particular embodiment, each modulation period is temporally offset from the previous modulation period by n time intervals.
Where n is greater than one, the control logic is further operative to define n groups of time intervals, associate each time interval in a modulation period to one of the groups, and then update the signals on a pixel in the row during an equal number time intervals assigned to each group during the row's modulation periods. In a more particular method, the control logic updates the signal on the pixel in (b/n) ones of the time intervals associated with each group during the pixel's modulation period, where b equals the number of bits in the multi-bit data word. Where the control logic defines multiple modulation periods for multiple rows, the control logic is further operative to update signals asserted on pixels in the same number of rows during each of the time intervals.
The control logic of the present invention is also operative to convert a binary-weighted data word (received via data input terminal set) into a compound data word having one or more binary bits and thermometer bits.
The display driver also includes components to debias the display and to discard bits of data words before the end of a rows respective modulation period. For example, where each pixel in the array includes a liquid crystal layer disposed between a common electrode and a pixel electrode, the display driver further includes a debias controller that provides a first debias signal indicative of a first bias direction for a first group of the time intervals in a pixel's modulation period and a second debias signal indicative of a second bias direction for a second group of time intervals. In another particular embodiment, the control logic is further operative to discard at least one bit of the multi-bit data word prior to the end of the modulation period and update the signal on the pixel based on any of the remaining bits such that the intensity value of the original data word is still asserted on the pixel.
Another aspect of the present invention facilitates 100% bandwidth and operation efficiency during each time interval in a frame. A particular method for driving an array of pixels includes the steps of defining a plurality of modulation periods during which electrical signals corresponding to particular intensity values will be asserted on pixels in rows of the array, associating each modulation period with at least one of the rows in the array, and then dividing each of the modulation periods into a plurality of coequal time intervals. In addition, the method also includes the steps of receiving a plurality of multi-bit data words that are each indicative of one of the intensity values that is asserted on a corresponding pixel and updating the electrical signals asserted on the pixels in an equal number of rows during each time. Usually less than all of the rows in the array are updated during each time interval. In a particular method, (b/n) rows are updated during each time interval, where b equals the number of bits in each multi-bit data word.
A display driver is also disclosed for carrying out this alternate aspect of the present invention. In particular, the display driver includes control logic that is operative to define a plurality of modulation periods during which electrical signals corresponding to intensity values can be asserted on pixels in the array. The control logic is also operative to associate each modulation period with at least one of the rows in the array, and divide each of the modulation periods into a plurality of time intervals. The display driver also includes a data input terminal set that receives a plurality of multi-bit data words that is each indicative of an intensity value to be asserted on a corresponding one of the pixels in the array. Responsive to the data words, the control logic is able to update the electrical signals on an equal number of rows during each time interval such that each intensity value defined a data word is asserted on the corresponding pixel in the array. In a particular embodiment, the control logic updates (b/n) rows of pixels during each time interval.
Yet another aspect of the present invention facilitates spreading any unused frame time between the time intervals in a modulation time period, thereby increasing the length of the time intervals. In particular, the method includes receiving a first synchronization signal, defining a time period during which electrical signals corresponding to intensity values will be asserted on pixels of an array, updating the electrical signals on the pixels a plurality of times during the time period such that each pixel displays the corresponding intensity value, and receiving a second synchronization signal that defines a time difference between the last time the electrical signals in a row were updated and the receipt of the second frame synchronization signal. The method further includes the steps of defining a second time period during which electrical signals will be asserted on the pixels in the rows of the array, updating the electrical signals asserted on the pixels in the rows a plurality of times during the second time period such that each of the pixels displays the corresponding intensity value, and spreading the time difference throughout the second time period based upon the number of times the electrical signals asserted on pixels in the rows of the display are updated during the second time period. Spreading the time difference throughout the second time period adjusts the duration of at least some of the time intervals in the second time period.
A display driver for driving a pixel array is also disclosed for carrying out this aspect of the present invention. In particular, the display driver includes a synchronization input terminal that receives a first, a second, and subsequent synchronization signals. The display driver also includes control logic the defines a first, a second and subsequent time periods during which electrical signals that correspond to intensity values are asserted on pixels in the rows of the array. The control logic updates the electrical signals asserted on the pixels in the rows a plurality of times during each time period such that the pixels display their corresponding intensity values. The display driver also includes a compensator that spreads the time difference between the last time the electrical signals were updated and a subsequent synchronization signal throughout the subsequent time periods based upon the number of times the electrical signals asserted on rows of pixels are updated during each subsequent time period. Spreading the time difference adjusts the length of at least some of the time intervals in the time periods.
Still another aspect of the present invention discloses a method for driving a display device having an array of pixels arranged in a plurality of columns and a plurality of rows. The method includes the steps of defining a modulation period for a row of pixels, dividing the modulation period into a plurality of time intervals equal to the quotient of the number of rows in the array and an integer (m), receiving a multi-bit data word that indicates an intensity value to be asserted on a pixel in the row, and updating the signal asserted on the pixel during at least some of the time intervals in the modulation period such that the intensity value defined by the multi-bit data word is displayed by the pixel. According to this aspect of the present invention, the value (m) is a divisor of the number of rows in the pixel array.
A novel display driver for this aspect of the present invention is also disclosed. The display driver includes a timer that generates a series of time values each associated with one of a plurality of time intervals, a data input terminal set that receives a multi-bit data word indicative of an intensity value to be asserted on the pixel, and control logic that defines a modulation period during which a signal corresponding to the intensity value will be asserted on the pixel and updates the signal during a plurality of the time intervals so that the pixel displays the intensity value. The control logic defines a modulation period with a number of time intervals equal to the quotient of the number of rows in the pixel array and (m), where (m) is a divisor of the number of rows in the pixel array.
Yet another aspect of the present invention relates to a method for driving a pixel array using multiple pixel control units. The method includes the steps of defining a plurality of modulation periods during which electrical signals corresponding to intensity values are asserted on pixels in the rows of an array, dividing each of the modulation periods into a plurality of time intervals, associating each of the rows in the array with one of a plurality of sets of rows, receiving a plurality of multi-bit data words indicative of intensity values, and updating the electrical signals asserted on the pixels in a plurality of rows during each time interval with a plurality of pixel control units. According to this method, each of the pixel control units update only the rows associated with a particular set of rows.
A novel display driver for this aspect of the present invention is also disclosed. The display driver includes a timer that generates a series of time values each associated with one of a plurality of time intervals, a data input terminal set for receiving a plurality of multi-bit data words that each defines an intensity value to be displayed by a corresponding pixel, and control logic having a plurality of pixel control units. The control logic is operative to define a plurality of modulation periods having a number of time intervals equal to n times the number of rows in the pixel array, to associate each row in the pixel array with one of the pixel control units, and to update the electrical signals asserted on at least some of the rows of pixels during each time interval with at least some of the pixel control units such that each pixel control unit updates only the rows associated with it.
The invention is also directed to non-transitory, electronically-readable storage media that store code for causing an electronic device to perform methods of the invention. The term “non-transitory” is intended to distinguish storage media from transitory electrical signals. However, rewritable memories are considered to be “non-transitory”.
The present invention is described with reference to the following drawings, wherein like reference numbers denote substantially similar elements:
This application discloses subject matter which is similar to the following co-pending U.S. patent applications, which are incorporated herein by reference in their entireties.
U.S. patent application Ser. No. 11/154,984, filed on Jun. 16, 2005, and entitled “Asynchronous Display Driving Scheme and Display”;
U.S. patent application Ser. No. 11/171,496, filed on Jun. 30, 2005, and entitled “Single Pulse Display Driving Scheme and Display”;
U.S. patent application Ser. No. 11/172,622, filed on Jun. 30, 2005, and entitled “System and Method for Discarding Data Bits During Display Modulation”;
U.S. patent application Ser. No. 11/172,621, filed on Jun. 30, 2005, and entitled “Display Driving Scheme and Display”;
U.S. patent application Ser. No. 11/172,382, filed on Jun. 30, 2005, and entitled “Display Debiasing Scheme and Display”; and
U.S. patent application Ser. No. 11/172,623, filed on Jun. 30, 2005, and entitled “System and Method for Using Current Pixel Voltages to Drive Display”.
The present invention overcomes the problems associated with the prior art, by providing a display and driving circuit and method wherein the bandwidth and power requirements of the display driver and imager are equalized over the entire frame. In the following description, numerous specific details are set forth (e.g., display start-up operations, particular bit schedules, etc.) in order to provide a thorough understanding of the invention. Those skilled in the art will recognize, however, that the invention may be practiced apart from these specific details. In other instances, details of well known display driving methods and components have been omitted, so as not to unnecessarily obscure the present invention.
The invention will be described first with reference to an embodiment where the imager includes only 48 rows in order to simplify the explanation of the basic aspects of the invention. Then, a more complicated embodiment of the invention where the display has 1112 rows will be described. It should be understood, however, that the invention can be applied to systems for displaying image data having any number of rows.
Display system 500 also includes a global timing control unit 512 that asserts clock signals and operational instructions on a global control bus 513 to coordinate the operation of display driver 502, imagers 504(r, g, and b) and frame buffers 506(A and B). For example, global timing control unit 512 asserts clock signals on bus 513, which the other components of display system 500 use to perform their various functions. Global timing control unit 512 generates clock signals at a frequency sufficient to allow the components of display system 500 to fully carry out their various functions. In addition, global timing control unit 512 receives operational codes (“opcodes”) from a system (not shown), decodes the opcodes into operational instructions, and asserts operational instructions (e.g., no-op instructions, data write commands, load row address commands, etc.) on bus 513 to administer the global operations of display system 500. According to the present invention, one important function of global timing control unit 512 is to spread unused frame time (caused by too high of a clock frequency) over the entire frame.
It should be noted that bus 513 is in communication with the various elements of display system 500. However, bus 513 is represented generally so as not to unnecessarily obscure the other aspects of the present invention.
Display driver 502 includes a data manager 514 and an imager control unit (ICU) 516. Data manager 514 is coupled to Vsync input terminal 508, video data input terminal set 510, and to bus 513 (not shown directly). In addition, data manager 514 is coupled to each of frame buffers 506(A) and 506(B) via 96-bit buffer data bus 518. Data manager 514 is also coupled to each imager 504(r, g, b) via a plurality (16 in the present embodiment) of imager data lines 520(r, g, b), respectively. Therefore, in the present embodiment, bus 518 has twice the bandwidth of imager data lines 520(r, g, b) combined. Finally, data manager 514 is coupled to a coordination line 522. Imager control unit 516 is also coupled to synchronization input 508 and to coordination line 522, and to each of imagers 504(r, g, b) via a plurality (15 in the present embodiment) of common imager control lines 524.
Display driver 502 controls and coordinates the driving process of imagers 504(r, g, b). Data manager 514 receives binary video data via video data input terminal set 510, separates the video data by color, converts the binary video data into compound video data having binary-coded and thermometer-coded video data, and provides the compound video data to one of frame buffers 506(A-B) via buffer data bus 518. Data manager 514 also retrieves video data from one of frame buffers 506(A-B) and provides each color (i.e., red, green, and blue) of video data to the respective imager 504(r, g, b) via imager data lines 520(r, g, b). Note that imager data lines 520 (r, g, b) each include 16 lines. As will be described later, each pixel is driven with an 8-bit compound data word. Therefore, two pixels worth of data can be transferred at once to each imager 504(r, g, b) via data lines 520(r, g, b). It should be understood, however, that a greater number of data lines 520 (r, g, b) could be provided to reduce the number of transfers required for each frame. Data manager 514 utilizes the coordination signals received via coordination line 522 to ensure that the proper data is provided to each of imagers 504(r, b, g) at the proper time. Finally, data manager 514 utilizes the synchronization signals provided at synchronization input 508 and the clock signals and instructions received via bus 513 to coordinate and route video data between the various components of display driving system 500.
Data manager 514 reads and writes data from and to frame buffers 506 (A and B) in alternating fashion. In particular, data manager 514 reads data from one of the frame buffers (e.g., frame buffer 506(A)) and provides the data to imagers 504 (r, g, b), while data manager writes the next frame of data to the other frame buffer (e.g., frame buffer 506(B)). After the first frame of data is written from frame buffer 506(A) to imagers 504 (r, g, b), then data manager 514 begins providing the second frame of data from frame buffer 506(B) to imagers 504(r, g, b), while writing the new data being received into frame buffer 506(A). This alternating process continues as data streams into display driver 502, with data being written into one of frame buffers 506(A-B) while data is read from the other of frame buffers 506(A-B).
Imager control unit 516 controls the modulation of the pixel cells of each imager 504(r, g, b). Imagers 504(r, g, b) are arranged such that video data provided by data manager 514 can be asserted to form a full color image once each of the colored images are superimposed. Imager control unit 516 supplies various control signals to each of imagers 504(r, g, b) via fifteen common imager control lines 524. Imager control unit 516 also provides coordination signals to data manager 514 via coordination line 522, such that imager control unit 516 and data manager 514 remain synchronized and the integrity of the image produced by imagers 504(r, g, b) is maintained. Finally, imager control unit 516 receives synchronization signals from synchronization input terminal 508, such that imager control unit 516 and data manager 514 are resynchronized with each frame of data.
Responsive to the video data received from data manager 514 and to the control signals received from imager control unit 516, imagers 504(r, g, b) modulate each pixel of their respective displays according to the video data associated with that pixel. Each pixel of imagers 504(r, g, b) are modulated with a reduced number of pulses, rather than a conventional pulse width modulation scheme. In addition, each row of pixels of imagers 504(r, g, b) are driven asynchronously such that the rows are processed during distinct modulation periods that are temporally offset. In addition, as will be described later, each modulation period is divided into a plurality of time intervals, such that an equal number of rows are updated during each time interval. These and other advantageous aspects of the present invention will be described in further detail below.
Although
According to one aspect of the present invention, data manager 514 converts 6-bit binary video data for each pixel in each imager 504(r, g, b) into a data word 602 subject to the following limitations. In particular, data manager 514 converts each binary-weighted data word into a compound data word 602 wherein the sum of the weighted values of the binary-coded bits 604 and the thermometer-coded bits 606 is equal to an integer multiple (n) of the number of rows of pixels in one of imagers 504(r, g, b). In the present embodiment, n is equal to one, and the number of rows in each imager 504(r, g, b) is forty-eight (48). Therefore, the sum of the weighted values of the bits in each combination data word 602 should equal forty-eight. A second requirement for this aspect of the present invention is that the number of bits, b, in the bit code of data word 602 is evenly divisible by n. Because n equals one in this embodiment, this limitation is automatically met. By setting the number of non-zero intensity values that can be defined by a compound data word 602 equal to an integer multiple of the number of rows in the imager's display, an equal number of rows in the display can be updated during each time interval. This facilitates 100% data efficiency between the display driver 502 and each imager 504(r, g, b).
According to a more particular aspect of the present invention that will be described in further detail later on, an imager includes a plurality of pixel control circuitries, each controlling the modulation of a set of rows in the display. To facilitate 100% operating efficiency of each pixel control circuitry in the imager, each pixel control circuitry must update the same number of rows in that single imager during each time interval. To ensure this result, data manager 514 converts binary data words into compound data words 602 according to the following additional limitations. First, the number of bits in the bit code of compound data word 602 must be evenly divisible by (s*n), where s is the number of pixel control circuitries in each imager. Second, the sum of the weighted values of the bits in the bit code of compound data word 602 must be evenly divisible by (s*n). Finally, an equal number of rows in the display assigned to each of the s sets must be updated during each time interval.
Assigning each row of pixels in the display in imagers 504(r, g, b) to one of two sets (i.e., s=2) provides a useful example. In particular, the even-numbered rows in a display can be assigned to one set and the odd-numbered rows in the display can be assigned to a second set. According to this example, data manager 514 converts binary data words into compound data words 602 having a number of bits evenly divisible by 2n. In addition, the sum of the weighted values of the bits in each data word 602 is evenly divisible by 2n. Finally, the bit code of data words 602 must produce row update schedules for each time interval wherein an equal number of even- and odd-numbered rows are updated during each time interval.
Note that the bit-code of compound data words 602 is completely arbitrary (in the number of bits and their respective weights) as long as the constraints described in the preceding paragraphs are satisfied depending on the aspect of the present invention that is implemented. In the present embodiment, data manager 514 converts each six bit binary-coded data word into an eight bit compound data word 602. Each compound data word 602 includes four binary-coded bits 604 having weighted values of 20, 21, 22, and 23. The remaining four thermometer-coded bits 606 would have weights of 9, 8, 8, and 8, respectively. Therefore, according to this example, the bit code (in weights) for each data word 602 is 1, 2, 4, 8, 9, 8, 8, 8.
This exemplary bit code for compound data word 602 meets all the constraints described above for n is equal to one and s is equal to two. For example, the sum of the weighted values equals forty-eight, which is equal to the number of pixel rows in each imager 504(r, g, b). Second, the number of bits (i.e., eight) in the bit code is evenly divisible by two (i.e., 2*1). In addition, the sum of the weights of the bit code (i.e., 48) is evenly divisible by two (i.e., 2*1). Finally, as will be described in greater detail below, an equal number of even-numbered and odd-numbered rows are updated during each time interval.
When data manager 514 receives a six-bit, binary-weighted data word for a particular pixel, data manager determines what intensity value the data represents, and then converts the six-bit data word into a combination data word 602 corresponding to the same intensity value. As will be described later, data manager 514 assigns a digital ON value or a digital OFF value to bits 604 and 606 such that the electrical signal written to a particular pixel will experience a number of pulse transitions that is less than or equal to the number of pulses experienced in conventional pulse-width modulation while still producing the desired intensity value.
At initial startup or after a video reset operation caused by the system (not shown), timer 702 is operative to start generating timing signals after receiving a first Vsync signal on synchronization input 710. In this manner, timer 702 is synchronized with data manager 514. Thereafter, timer 702 provides timing signals to data manager 514 via bus 712 and coordination line 522, such that data manager 514 remains synchronized with imager control unit 516. Once data manager 514 receives the first synchronization signal via synchronization input 508 and the first timing signal via coordination line 522, data manager 514 begins transferring video data as described above.
Address generator 704 provides row addresses to each of imagers 504(r, g, b) and to time adjuster 708. Address generator 704 has a plurality of inputs including a synchronization input 714, a timing input 716, and a plurality of outputs including 6-bit address output bus 718, and a single bit load data output 720. Synchronization input 714 is coupled to receive the Vsync signal from synchronization input 508 of display driver 502, and timing input 716 is coupled to time value output bus 712 of timer 702 to receive timing signals therefrom. Responsive to receiving timing values via timing input 716, address generator 704 is operative to generate row addresses and to consecutively assert the row addresses on address output bus 718. Address generator 704 generates 6-bit row addresses and asserts each bit of the generated row addresses on a respective line of address output bus 718. Furthermore, depending on whether the row address generated by address generator 704 is a “write” address (e.g., to write data into imager memory) or a “read” address (e.g., to read data from imager memory), address generator 704 will assert a load data signal on load data output 720. In the present embodiment, a digital HIGH value asserted on load data output 720 indicates that address generator 704 is asserting a write address on address output bus 718, while a digital LOW value indicates a read address. The reading and writing of data from/to memory of the display will be described in greater detail below.
Time adjuster 708 adjusts the time value output by timer 702 based on the row address received from address generator 704. Time adjuster 708 receives 6-bit time values from bus 712, load data signals from load data output 720 of address generator 704, and 6-bit row addresses from address output bus 718 of address generator 704. Time adjuster 708 outputs 6-bit adjusted time values on adjusted timing output bus 722.
Responsive to the signal asserted on load data output 720 and the row address asserted on address output bus 718, time adjuster 708 adjusts the time values asserted on bus 712 and asserts the adjusted time value on adjusted timing output bus 722. The load data value asserted on output 720 indicates to time adjuster 708 whether the row address asserted on bus 718 is a write address (e.g., a digital HIGH signal) or a read address (e.g., a digital LOW signal). Time adjuster 708 adjusts the time values asserted on bus 712 only for read row addresses. Accordingly, when the load data signal asserted on output 720 is HIGH, indicating that a write address is being output by address generator 704, time adjuster 708 ignores the row address and does not update the adjusted timing value output on adjusted timing output bus 722.
Time adjuster 708 can be created from a variety of different components, however in the present embodiment, timing adjuster 708 is a subtraction unit that decrements the time value output by timer 702 based upon the row address asserted on row address output bus 718. In another embodiment, time adjuster 708 is a look-up table that returns an adjusted time value depending on the time value asserted on bus 712 and the row address received on bus 718.
Debias controller 706 controls the debiasing process of each of imagers 504(r, g, b) in order to prevent deterioration of the liquid crystal material therein. Debias controller 706 is coupled to time value output bus 712 and includes a common voltage output 726 and a global data invert output 726. Debias controller 706 receives timing signals from timer 702 via bus 712, and depending on the value of the timing signal, asserts one of a plurality of predetermined voltages on common voltage output 724 and a HIGH or LOW global data invert signal on global data invert output 726. The voltage asserted by debias controller 706 on common voltage output 724 is asserted on the common electrode (e.g., an Indium-Tin Oxide (ITO) layer) of the pixel array of each of imagers 504(r, g, b). In addition, the global data invert signals asserted on global data invert output 726 determine whether data asserted on each of the electrodes of the pixel cells of imagers 504(r, g, b) is asserted in a normal or inverted state.
The operation of debias controller 706 is discussed in detail in U.S. patent application Ser. No. 11/172,382, filed on Jun. 30, 2005, and entitled “Display Debiasing Scheme and Display,” which is incorporated herein by reference in its entirety. Indeed, debias controller 706 can employ any of the debiasing methods described in U.S. Ser. No. 11/172,382 to effectively debias the pixel arrays of imagers 504(r, g, b).
Finally, imager control lines 728 convey the outputs of the various elements of imager control unit 516 to each of imagers 504(r, g, b). In particular, imager control lines 728 include adjusted timing output bus 722 (six lines), address output bus 718 (six lines), load data output 720 (one line), common voltage output 724 (one line), and global data invert output 726 (one line). Accordingly, imager control lines 728 are composed of fifteen control lines, each providing signals from a particular element of imager control unit 516 to each imager 504(r, g, b). Each of imagers 504(r, g, b) receive the same signals from imager control unit 516 such that imagers 504(r, g, b) remain synchronized.
Note that because display data input 822 includes sixteen lines, two, eight-bit compound data words 602 (i.e., two pixels worth of data) can be received simultaneously. It should be understood, however, that in practice, more data lines can be provided to increase the amount of data that can be transferred at one time. The numbers have been kept relatively low in this example, for the sake of clear explanation.
Shift register 802 receives and temporarily stores display data for a single row 814 of pixel cells 810. Display data is written into shift register 802 sixteen bits at a time via data input 822 until display data for a complete row 814 has been received and stored. In the present embodiment, shift register 802 is large enough to store eight bits (i.e., one combination data word 602) of video data for each pixel cell 810 in a row 814. In other words, shift register 802 is able to store 15,616 bits (e.g., 1952 pixels/row×8 bits/pixel) of video data. Once shift register 802 contains data for a complete row 814 of pixel cells 810, the data is transferred from shift register 802 into circular memory buffer 804 via data lines 836 (1952×8).
Circular memory buffer 804 receives rows of 8-bit display data output by shift register 802 on data lines 836, and stores the video data for an amount of time sufficient for a signal corresponding to the grayscale value of the data to be asserted on an appropriate pixel 810 of display 808. Responsive to control signals, circular memory buffer 804 asserts the 8-bit display data associated with each pixel 810 of a row 814 onto data lines 838 (1952×8).
To control the input and output of data, circular memory buffer 804 includes a single-bit load input 840 and a 28-bit address input 842. Depending on the signals asserted on load input 840 and address input 842, circular memory buffer 804 either loads a row of 8-bit compound data words 602 being asserted on data lines 836 from shift register 802 or provides a row of previously stored 8-bit compound data words 602 to row logic 806 via data lines 838 (1952×8). For example, if a signal asserted on load input 840 was HIGH indicating a write address was output by address generator 704, then circular memory buffer 804 loads the bits of video data asserted on data lines 836 into memory. The memory locations into which the bits are loaded are determined by address converter 816, which asserts converted memory addresses onto address inputs 842. If on the other hand, the signal asserted on load input 840 is LOW, indicating a read row address output by address generator 704, then circular memory buffer 804 retrieves a row of 8-bit compound data words 602 from memory and asserts the data onto data lines 838. The memory locations from which the previously stored display data are obtained are also determined by address converter 816, which asserts converted read memory addresses onto address inputs 842.
Row logic 806 writes single bits of data to the pixels 810 of display 808 depending on the adjusted time value received on adjusted timing input 830. Row logic 806 receives an entire row of 8-bit compound data words 602 via data lines 838, and based on the display data and adjusted time value, updates the single bits asserted on pixels 810 of the particular row 814 via display data lines 844. Row logic 806 writes appropriate single-bit data to each pixel 810 in a row 814, such that the duration of the pulse(s) on each pixel equal the intensity value defined by an associated compound data word 602.
It should be noted that row logic 806 updates each row 814 of display 808 a plurality of times during the row's modulation period in order to assert the intensity value on each pixel 810 for the proper duration. The process of updating a row 814(0-47) involves row logic 806 updating the electrical signals on each pixel 810 in a particular row 814(0-47). Therefore, the phrase “updating a row” is intended to mean row logic 806 updating the single bit data stored in and asserted on each pixel 810 in the particular row 814(0-47).
It should also be noted that, in the present embodiment, row logic 806 is a “blind” logic element. In other words, row logic 806 does not need to know which row 814 of display 808 it is processing. Rather, row logic 806 receives an 8-bit compound data word 602 for each pixel 810 of a particular row 814 and an adjusted time value on adjusted timing input 830. Based on the display data and the adjusted time value, row logic 806 writes the appropriate bit of compound data words 602 to the pixels 810 for the particular adjusted time value.
Display 808 is a reflective or transmissive liquid crystal display (LCD), having 1952 columns 812 and 48 rows 814 of pixel cells 810. Each row 814 is enabled by an associated one of a plurality of word lines 846. Because display 808 includes 48 rows of pixels 810, there are also 48 word lines 846. In addition, one data line 844 communicates data between row logic 806 and each column 812 of display 808 to an enabled pixel 810 in the particular column.
Display 808 also includes a common electrode (e.g., an Indium-Tin-Oxide layer, not shown) overlying all of pixels 810. Voltages can be asserted on the common electrode via common voltage input 826. In addition, the voltage asserted on each pixel 810 by the single bit stored therein can be inverted (i.e., switched between normal and inverted values) depending upon the signal asserted on global data invert input 824. The signal asserted on global data invert input 824 is provided to each pixel cell 810 of display 808.
The signals asserted on global data invert terminal 824 and the voltages asserted on common voltage input 826 are used to debias display 808. As is well known in the art, liquid crystal displays will degrade due to ionic migration in the liquid crystal material when the net DC bias across the liquid crystal is not zero. Such ionic migration degrades the quality of the image produced by the display. By debiasing display 708, the net DC bias across the liquid crystal layer is retained at or near zero and the quality of images produced by display 708 is kept high. Again, a debiasing process for use with the present invention is described in greater detail in U.S. patent application Ser. No. 11/172,382 entitled “Display Debiasing Scheme and Display.”
Row decoder 816 asserts a signal on one of word lines 846 at a time, such that the single bit data asserted by row logic 806 on display lines 844 is latched into the enabled row 814 of pixels 708. Row decoder 816 receives a 6-bit row address from address input 832 and a disable signal (i.e., the load data signal) via load data input 834. Note that a 6-bit row address is required to uniquely define each of the 48 rows 814 of display 808. Depending upon the row address received on address input 832 and the value of the signal received on load data input 834, row decoder 816 is operative to enable one of word lines 846 (e.g., by asserting a digital HIGH value). A digital HIGH value asserted on load data input 834 indicates that the row address received by row decoder 816 is a “write” address, and that data is being loaded into circular memory buffer 804. Accordingly, when the signal asserted on load data input 834 is a digital HIGH, then row decoder 816 ignores the row address asserted on address input 832 and does not enable a new one of word lines 846. On the other hand, if the signal on load data input 834 is a digital LOW, then row decoder 816 enables one of word lines 750 associated with the row address asserted on address input 832.
Address converter 818 receives the 6-bit row addresses via address input 832, converts each row address into a plurality of memory addresses, and provides the memory addresses to circular memory buffer 804. In particular, address converter 818 provides a memory address for each bit of display data, which are stored independently in circular memory buffer 804. For example, in the present 8-bit driving scheme, address converter 818 converts a row address received on address input 832 into eight different memory addresses, each associated with a different bit of data word 602. Depending upon the load data signal asserted load data input 834, circular memory buffer 804 loads data into or retrieves data from the particular locations in circular memory buffer 804 identified by the memory addresses output by address converter 818 for each bit of display data.
Finally, it should be noted that the components of imager 504(r, g, b), other than display 808, comprises the pixel control circuitry that carries out the modulation of display 808. As will be discussed in greater detail below, a single imager 504(r, g, b) can include multiple pixel control circuitries where each pixel control circuitry is responsible for modulating a defined set of rows in display 808. Incorporating multiple iterations of the pixel control circuitry in a single imager 504(r, g, b) advantageously reduces the number of operations that a single iteration of pixel control circuitry would have to perform. In other words, an imager 504(r, g, b) including multiple pixel control circuitries can update pixels more times per frame than can an imager 504(r, g, b) with only one pixel control circuitry.
When updating a particular row 814 of pixels 810, each bit select logic 904(0-1951) receives a full compound data word 602 from circular memory buffer 804 via a respective set of data lines 838(0-1951) for a particular column 812 of pixels 810. In addition, each bit select logic 904(0-1951) also receives an adjusted time value via adjusted timing input 830 for the particular row 814 of pixels 810. Depending on the adjusted time value asserted on adjusted timing input 830, each bit select logic 904(0-1951) selects the appropriate bit of the compound data word 602 for the particular pixel 810 in the associated column 812 and asserts that bit (i.e., either a digital ON value or a digital OFF value) on the respective data line 844(0-1951). The selection process of bit select logic 904 will be described in further detail below.
Electrical signals corresponding to particular intensity values are written to the pixels in each row 814(0-47) by row logic 806 within the row's respective modulation period. Because the number of rows 814(0-47) is equal to the number of time intervals 1002(0-47), each row 814(0-47) has a modulation period that begins at the beginning of one of time intervals 1002(0-7) and ends after the lapse of forty-eight time intervals 1002(0-47) thereafter. Accordingly, the modulation periods of rows 814(0-47) are equal in duration. For example, row 814(0) has a modulation period that begins at the beginning of time interval 1002(0) and end after the lapse of time interval 1002(47). Row 814(1) has a modulation period that begins at the beginning of time interval 1002(1) and ends after the lapse of time interval 1002(0). Row 814(2) has a modulation period that begins at the beginning of time interval 1002(2) and ends after the lapse of time interval 1002(1). This trend continues for the modulation periods for rows 814(3-46), ending with the row 814(47), which has a modulation period starting at the beginning of time interval 1002(47) and ending after the lapse of time interval 1002(46). The beginning of each row 814's modulation period is indicated in
The modulation period for each row 814(0-47) is temporally offset with respect to every other row 814(0-47) in display 808. For example, the modulation period of row 814(1) is temporally offset with respect to the modulation period of row 814(0) by one time interval 1002. Similarly, the modulation period of row 814(2) is temporally offset from the modulation period of row 814(1) by one time interval 1002. Likewise, the modulation period of row 814(3) is temporally offset from the modulation period of row 814(2) by one time interval 1002. This pattern continues for the remaining rows 814(4-47) of display 808. Thus, the rows of the display are driven asynchronously. Stated another way, signals corresponding to gray scale values of one frame of data will be asserted on the pixels of some rows at the same time signals corresponding to grayscale values from a preceding or subsequent frame of data are asserted on other rows. According to this scheme, the system begins to assert image signals for one frame of data on some rows of display 808 before the previous frame of data is completely asserted on other rows. Stated yet another way, a particular row 814's modulation period is temporally offset from the preceding row's modulation period by n time intervals.
It should be noted that the modulation period associated with each row 814(0-47) forms a frame time for that row 814(0-47). Accordingly, signals corresponding to a complete intensity value are written to each row 814(0-47) during each row's own frame time. However, data can be written to pixels 810 more than once per frame. For example, a row's frame time may include a multiple (e.g., two, three, four, etc.) of modulation periods, such that data is written to each pixel 808 of a row repeatedly during the frame time of that row 814. Writing data multiple times during each row's frame time significantly reduces flicker in the image produced by display 808.
It should also be noted that the modulation periods assigned to the rows 814 can be mixed up rather than be in the consecutive order that is shown in chart 1000. For example, a different row (e.g., row 814(28)) could be assigned to the modulation period associated with row 814(0). Indeed, the row 814 that is assigned to each modulation period can be arbitrary as long as it is carried through to any other components (e.g., data manager 514, address generator 704, etc.) that rely on the same modulation period assignments.
A third column 1106 indicates an update schedule for data word 602's bit code. In particular, a bit in column 1102 is written to a particular pixel 810 during the update time interval 1002 in column 1106 in that pixel's modulation period. Note that the update time intervals 1002 given in column 1106 are for an unadjusted modulation period. In other words, the update time intervals 1002 in column 1106 assume that the pixel's modulation period begins at time interval 1002(0) and ends after time interval 1002(47). For example, B0 is written to a pixel 810 during time interval 1002(0) in that pixel's modulation period. Similarly, bits B1, B2, B3, B4, B5, B6, and B7 are written to pixel 810 in time intervals 1002(1), 1002(3), 1002(7), 1002(15), 1002(24), 1002(32), and 1002(40), respectively, in the same pixel's modulation period.
In general, a particular bit in column 1102 will be written to pixel 810 during a time interval 1002(x) in that pixel's modulation period, where x is equal to the sum of the weights of the bits previously written to pixel 810. For example, bit B3 is written to pixel 810 in time interval 1002(7) in that pixel's modulation period. Note that the sum of the weights of B0-B2 is equal to 7 (i.e., 1+2+4=7). Similarly, B6 is written to pixel 810 in time interval 1002(32) because the sum of the weights of bits B0-B5 is equal to 32 (i.e. 1+2+4+8+9+8=32).
As stated above, the bit code in column 1102 is completely arbitrary as long as it meets the constraints set forth above in
The bit code for data words 602 in column 1104 also ensures that if imagers 504(r, g, b) contained two iterations of pixel control circuitry (i.e., s equals two), then an equal number of even- and odd-numbered rows will be updated during each time interval. For example, the sum of the weights in column 1104 is evenly divisible by two, and the number of bits in code 1104 is also evenly divisible by two. In addition, the update time intervals in column 1106 indicate that the bit code in column 1104 produces row schedules where an equal number of rows 814 assigned to a first set (e.g., even-numbered rows) and a second set (e.g., odd-numbered rows) are updated during each time interval 1002. Column 1106 indicates the number of even and odd rows 814 that are updated during each time interval 1002 because the number of rows 814 and the number of time intervals 1002 are equal. In this example, column 1106 contains four even update time intervals 1002(0), 1002(24), 1002(32), and 1002(40) and four odd update time intervals 1002(1), 1002(3), 1002(7), and (15). Therefore, four even-numbered rows and four odd-numbered rows 814 will be updated during each time interval 1002.
Also note that in the present embodiment, the binary bits 604 are able to define 16 intensity values and have a combined bit weight equal to 15 (i.e., 1+2+4+8=15). Accordingly, although it is not necessary, it is beneficial to assign each thermometer bit 606 a weight that is less than or equal to the combined weight of binary bits 604 to ensure that all intensity values can be defined by data word 602. It should also be noted that the number of thermometer bits 606 can be reduced (i.e., by increasing the thermometer bits' weights) while still generating all intensity values if row logic 806 could read the prior pixel value and use the prior value and the at least one bit of data word 602 to determine a new value to assert on the pixel. This pixel-read process is described in U.S. patent application Ser. No. 11/172,623 which is entitled “System and Method for Using Current Pixel Voltages to Drive Display” and is incorporated herein by reference. Reducing the number of thermometer bits 606 in turn reduces the bandwidth required to drive imager 504 and display 808.
Finally, it should also be noted that bits in column 1102 and the weights in column 1104 can be arranged in any particular order in table 1100. However, to maintain uniformity in the display image, the order should not be changed once the update time intervals in column 1106 have been calculated.
Generally, the row schedule for each time interval 1002(0-47) is determined by the following formula:
Row=(r−T_event)+τ,
where “Row” denotes a row 814 that will be updated during the particular time interval 1002(τ), (r) represents the total number of rows 814 in display 808, T_event is the update time interval in column 1106, 1204 for a particular bit, and (τ) is the number of the time interval 1002 that the row schedule is being calculated for. In the present embodiment, r equals forty-eight because there are forty-eight rows 814 in display 808, the T_Event values are given in column 1204, and τ can be any number ranging from zero to forty-seven which correspond to time intervals 1002(0-47). Note that the value Row is constrained between zero to forty-seven because there are only forty-eight rows in display 808. Therefore, when subtracting or adding in the above equation, the value of (r−T_Event) or Row should not go negative or above forty-seven, but should loop forward or backward to the appropriate row value between zero and forty-eight inclusive.
Column 1206 shows the row schedule for time interval 1002(0) (i.e., τ=0) which was calculated from the equation given above. During time interval 1002(0), B0 bits are written to each pixel 810 in row 814(0), B1 bits are written to each pixel 810 in row 814(47), B2 bits are written to each pixel 810 in row 814(45), B3 bits are written to each pixel 810 in row 814(41), B4 bits are written to each pixel 810 in row 814(33), B5 bits are written to each pixel 810 in row 814(24), B6 bits are written to each pixel 810 in row 814(16), and B7 bits are written to each pixel 810 in row 814(8). Note that four even-numbered rows 814 and four odd-numbered rows 814 are updated during time interval 1002(0).
Similarly, the row schedule for time interval 1002(1) (i.e., τ=1) shown in column 1208 indicates that B0 bits are written to each pixel 810 in row 814(1), B1 bits are written to each pixel 810 in row 814(0), B2 bits are written to each pixel 810 in row 814(46), B3 bits are written to each pixel 810 in row 814(42), B4 bits are written to each pixel 810 in row 814(34), B5 bits are is written to each pixel 810 in row 814(25), B6 bits are written to each pixel 810 in row 814(17), and B7 bits are written to each pixel 810 in row 814(9). Again, note that four even-numbered rows and four odd-numbered rows are updated during time interval 1002(1).
This trend continues for the remaining time intervals. For instance, in time interval 1002(2) shown in column 1210, bits B0-B7 are written to rows 814(2), 814(1), 814(47), 814(43), 814(35), 814(26), 814(18), and 814(10), respectively, for each pixel in those rows. The row schedules for time interval 1002(3) and 1002(4) are given in columns 1212 and 1214, respectively. Again, the bit code of data word 602 facilitates four even- and four odd-numbered rows 814 to be updated during each time interval 1002.
It should be noted that because the number of time intervals 1002 is equal to n times the number of rows 814, the row schedule for each time interval 1002 will contain a number of row updates equal to the number of bits (b) in data word 602 divided by n (i.e., b/n). In this case, where b equals eight and n equals one, there are eight rows 814 are updated during each time interval 1002(0-47).
Chart 1300 illustrates several aspects of the driving scheme of the present invention. In particular, chart 1300 indicates when each of bits B0-B7 are written to a row 814 of pixels during that row's modulation period. In addition, chart 1300 indicates which rows are updated during each time interval 1002(0-47) independent of their modulation period. A box in chart 1300 with a number in it indicates the bit that is written to a row 814 in an associated row of chart 1300 during the time interval 1002 in the same column. For example, B4 bits are written to row 814(8) during time interval 1002(23). As another example, B7 bits are written to row 814(39) during time interval 1002(31).
Looking across the rows in chart 1300, particular bits of a compound data word 602 are written to a row 814 based on their weight within that row's modulation period. For example, row logic 806 updates row 814(0) during time intervals 1002(0), 1002(1), 1002(3) 1002(7), 1002(15), 1002(24), 1002(32) and 1002(40). Note that the time between when particular bits are written to row 814(0) corresponds to the weights of the individual bits in the bit code of data word 602. For example, bit B4 has a weight of 9 time intervals 1002, and there are 9 time intervals 1002 between when row logic 806 writes B4 and when row logic 806 writes B5 to row 814(0).
The remaining rows 814(1-47) are updated during the same time intervals 1002(0-47) as row 814(0) when the time intervals 1002(0-47) are adjusted for a particular row's modulation period. For example, with the time intervals 1002(0-47) numbered as shown, row 814(1) is updated during time intervals 1002(1), 1002(2), 1002(4), 1002(8), 1002(16), 1002(25), 1002(33), and 1002(41). However, row 814(1) has a modulation period beginning one time interval later than row 814(0). If the time intervals 1002(0-47) were adjusted (i.e., by subtracting one from each time interval) such that row 814(1) became the reference row, then row 814(1) would be updated during time intervals 1002(0), 1002(1), 1002(3), 1002(7), 1002(15), 1002(24), 1002(32), and 1002(40), which are the same as row 814(0). Therefore, each row 814(0-47) is updated at different times when viewed with respect to one particular row's (i.e., row 814(0)) modulation period, however each row 814(0-47) is updated according to the same algorithm. The algorithm just starts at a different time for each row 814(0-47).
In addition, regardless of modulation period, each column in chart 1300 shows a row schedule for each time interval 1002(0-47). For example, the first five columns indicate the row schedules shown in columns 1206, 1208, 1210, 1212, and 1214 in
Row logic 806 and row decoder 816, under the control of signals provided by imager control unit 516 (
As row logic 806 is asserting data bits on data lines 844 during a time interval 1002, row decoder 816 receives row addresses from address input 832 that are associated with the rows 814(0-47) of pixels that are being updated during the particular time interval 1002. For each row address received and where the load data signal on load data input 834 is LOW, row decoder 816 decodes the row address and enables the word line 846(0-47) associated with the particular row 814(0-47) that needs to be updated. Each pixel 810 in the enabled row 814 then latches the data asserted on the respective data line 844 and asserts the latched data onto its pixel electrode.
Time adjuster 708 (
It should be noted that time adjuster 708 does not produce negative time values, but rather loops the time value back to 47 to finish the time adjustment if the adjustment value needs to be decremented below a value of zero. For example, if timer 702 generated a value of 11 and time adjuster 708 received a row address associated with row 814(19), then time adjuster 610 would output an adjusted time value of 40. The time value of 40 is the time in row 814(19)'s (adjusted) modulation period when bit B7 should be written to the pixels in row 814(19).
Because each bit B0-B7 is written to a row 814(0-47) during the same time intervals in that row's respective modulation period, time adjuster 708 need only output eight different adjusted time values. In the present embodiment, the adjusted time values are 0, 1, 3, 7, 15, 24, 32, and 40. Depending on what adjusted time value row logic 806 receives determines what bit row logic 806 outputs. For example, if row logic 806 receives an adjusted time value of 0, then row logic outputs B0 onto data lines 844(0-1951). Similarly, if row logic 806 receives an adjusted time value of 24, then row logic 806 asserts bits B5 for an entire row of pixels onto data lines 844(0-1951). This process occurs eight times per time interval 1002. Row logic 806 does not need to know which row it is updating because the adjusted time value alone tells row logic 806 which bit plane to assert for each pixel in a row 814 on data lines 844.
Note that the adjusted time values are the same update time intervals shown in column 1106 in
Row logic 806 sequentially updates each row 814(0-47) of display 808 that is supposed to be updated in a particular time interval 1002(0-47). For example, during time interval 1002(0), row logic 806 will update rows 814(0), 814(8), 814(16), 814(24), 814(33), 814(41), 814(45), and 814(47). The particular order that row logic 806 updates the rows 814 in each time interval 1002(0-47) can be predefined or arbitrary. However, row logic 806 must update all rows 814 scheduled in a particular time interval 1002 before the time interval has lapsed.
The update schedule in column 1106 in
In general, a bit of data is stored in circular memory buffer 804 only as long as the bit is needed for row logic 806 to assert the bit onto an associated pixel 810. Therefore, the size of a memory section associated with a particular bit is calculated based on the same principle. Note from column 1106 in
Therefore, because bit B0 associated with a pixel 814 is no longer needed after time interval 1002(0), bit B0 can be discarded (or over-written) after the lapse of time interval 1002(0). Similarly, bit B1-B7 can be discarded (e.g., over-written) any time after the lapse of time intervals 1002(1), 1002(3), 1002(7), 1002(15), 1002(24), 1002(32), and 1002(40), respectively.
The size of each memory section of circular memory buffer 804 for a particular column of pixels depends on the number of bits in each data word 602 and the number of time intervals 1002 that a particular bit is needed in a modulation period. Accordingly, each column 812 in display 808 needs the following amounts of memory in circular memory buffer 804:
Therefore, circular memory buffer 804 contains (1952×1) bits of memory for B0 bits, (1952×2) bits of memory for B1 bits, (1952×4) bits of memory for B2 bits, (1952×8) bits of memory for B3 bits, (1952×16) bits of memory for B4 bits, (1952×25) bits of memory for B5 bits, (1952×33) bits of memory for B6 bits, and (1952×41) bits of memory for B7 bits. As a result, circular memory buffer 804 contains 253.8 Kbits of memory. In contrast, if circular memory buffer 804 was a prior-art frame buffer that stored 8 bits of video data for each pixel for the entire frame, it would contain 749.6 Kbits of data. Therefore, circular memory buffer 804 is approximately 34% the size of a prior art input buffer (like buffer 110), and therefore requires substantially less area on imager 504(r, g, b). Finally, it should be noted that the above values assume that one row 814 of new video data is written to circular memory buffer 804 during each time interval 1002.
It should also be noted that additional memory-saving alterations can be made to the present invention. For example, the size of circular memory buffer 706 can be reduced if different bits of particular data words 1202 are written to circular memory buffer 706 at different times. As another example, circular memory buffer 804 could be situated outside imager 504 and transfer bits directly to row logic 806. In such a case, memory in the imager 504 could be reduced at the expense of higher bandwidth between display driver 502 and imagers 504(r, g, b).
Those skilled in the art will realize that the specific amounts of memory associated with each section of circular memory buffer 706 can be modified as necessary. For example, the amount of memory in each memory section might be increased to conform with a standard memory size and/or standard counters, or to account for data transfer timing requirements. As another example, the size of one memory section could be increased while the size of another memory section could be reduced. Indeed, many modifications are possible. Furthermore, the functionality of circular memory buffer 804 is discussed in more detail in U.S. patent application Ser. No. 11/172,622 entitled “System and Method for Discarding Data Bits During Display Modulation,” which is incorporated by reference in its entirety.
Address converter 818 indicates to circular memory buffer 804 the locations to store and retrieve each bit of display data based on the 6-bit row address it receives via address input 832 and the size of each section of circular memory buffer 804. Address converter 818 converts the 6-bit row address received via input 832 into a memory address for each section of memory in circular memory buffer 804 associated with a bit of data word 602. The converted memory addresses are then asserted onto address input 842 such that circular memory buffer 804 either loads data into or reads data from the associated memory locations within circular memory buffer 804. In particular, address converter 818 uses the following algorithms to convert a row address into a memory address for each bit of data word 602 stored in circular memory buffer 804:
The number of lines in address input 842 is determined based on the size of the memory section for each bit in data word 602. In particular, one line is needed to uniquely address each memory location for both bits B0 and B1, two lines are needed to uniquely address each memory location for bits B2, three lines are needed to uniquely address each memory location for bits B3, four lines are needed to uniquely address each memory location for bits B4, five lines are needed to uniquely address each memory location for bits B5, and six lines are needed to uniquely address each memory location for bits B6 and B7. Accordingly, address input 842 includes twenty-eight address lines. It should be noted that because B0 only requires one bit of memory (for each column 812 of pixels 810), this bit of memory does not necessarily need to be separately addressed. Rather, each B0 bit can be written into circular memory buffer 804 in the same B0 memory location, thereby eliminating one line from address input 842. However, address input 842 is shown to include twenty-eight lines for ease of explanation.
According to the present invention, the number of pulses needed to write an intensity value to a pixel is equal to or less than the conventional PWM scheme. For example, intensity values 1402(4) and 1402(5) are written to a pixel 810 with the same number of pulse transitions (i.e., two and four transitions respectively) as a convention PWM scheme. In contrast, intensity value 1402(17) is written with only two pulse transitions, whereas to write the same intensity value using conventional PWM requires four pulse transitions. Therefore, the present driving method advantageously reduces the number of pulse transitions required to assert some intensity values 1402 over conventional PWM methods.
It should be noted that data manager 514 has the flexibility to define intensity values 1402(0-48) based on the bit coding of compound data word 602. In particular, depending on the number and respective weights of binary-coded bits 604 and thermometer-coded bits 606 in data word 602, data manager 514 may be able to define particular intensity values 1402 in several ways. For example, intensity value 1402(17) can be defined as shown where B3=1 (weight=8) and B4=1 (weight=9). The result is a single pulse waveform that can be asserted on a pixel 810 with a single pulse (i.e., only two transitions in the electrical signal). In contrast, intensity value 1402(17) can also be defined by setting B0=1 (weight=1), B3=1 (weight=8), and B5=1 (weight=8), which requires three different pulses, and six transitions in the electrical signal asserted on pixel 810. Accordingly, depending on the bit code of compound data word 602, data manager 514 can be configured to assign values to the particular bits of compound data word 602 to produce a grayscale value 1402 with the fewest number of pulse transitions possible. In any case, data manager 514 is not limited in how it defines particular intensity values 1402, but may be configured to define intensity values 1402 depending on specific design goals or driver requirements.
The intensity waveforms 1402(0-48) also indicate the particular bit (i.e., one of B0-B7) that row logic 806 writes to particular pixel 810 at a particular time interval 1002(0-47). As described above, because only one bit of a data word 602 is required to turn a pixel ON or OFF during a particular time interval 1002, the present invention facilitates a significant reduction in the memory requirement of imagers 504, as described above.
A general description of the operation of display driving system 500 will now be provided with reference to
Initially, at startup or upon a video reset, data manager 514 receives a first Vsync signal via synchronization input terminal 508 and a first timing signal via coordination line 522 from timer 602, and begins supplying display data to imagers 504(r, g, b). To provide display data to imagers 504(r, g, b), data manager 514 receives video data from video data input terminal 510, divides the video data based on color (e.g., red, green, and blue) into, converts the display data into compound data word 602 including binary-coded bits 604 and thermometer-coded bits 606, temporarily stores the compound data words 602 in frame buffer 506A, subsequently retrieves the video data from frame buffer 506A (while writing the next frame of data to frame buffer 506B), and provides the appropriate colored video data to each of imagers 504(r, g, b) via the respective imager data lines 520(r, g, b). Accordingly, before or during a particular timing signal value (e.g., 0-47), data manager 514 supplies display data to each of imagers 504(r, g, b) for each pixel 810 of a row 814 whose modulation period begins in the particular time interval 1002. Because the number of non-zero intensity values (and thus time intervals 1002) are equal to the number of rows 814 of pixels 810 in display 808, data manager 514 provides colored display data to imagers 504(r, g, b) at a rate that is sufficient to provide at least one row 814 of video data to imagers 504(r, g, b) within the duration of one of time intervals 1002(0-47).
Colored video data is received by each imager 504(r, g, b) via data input 822 and is loaded into shift register 802 sixteen bits at a time. When enough video data is accumulated for an entire row 814 of pixels 810, shift register 802 outputs eight bits of video data (e.g., a compound data word 602) for each pixel 810 on a respective one of the 1952×8 data lines 836. The video data output from shift register 802 is loaded into circular memory buffer 804.
Circular memory buffer 804 loads the data asserted on data lines 836 when a HIGH “load data” signal is generated by address generator 704 of imager control unit 516 and asserted on load input 840. A row address associated with the video data asserted on data lines 836 is simultaneously generated by address generator 704 and is asserted on address input 832. The address is converted by address converter 818 into a memory address associated with circular memory buffer 804. Then a memory address associated with each bit of data word 602 for each pixel 810 is asserted on address input 842 of circular memory buffer 804 such that each bit of the 8-bit data word 602 is stored in an associated memory location in circular memory buffer 804.
When circular memory buffer 804 receives memory addresses from address converter 818 and the signal on load input 840 is LOW, then circular memory buffer 804 outputs video data for each pixel 810 in a row 814 associated with the converted row address to row logic 806 via data lines 838. Each logic unit 902(0-1951) in row logic 806 receives and temporarily stores the 8-bit combination data word 602 associated with one of pixels 810. Row logic 806 simultaneously receives a 6-bit adjusted time value via adjusted timing input 830 indicative of an adjusted time interval for the particular row 814 that is going to be updated. Based on the adjusted time value, each of bit select logics 904(0-1951) selects a bit and assert the selected bit on a respective one of data lines 844(0-1951).
Row decoder 816 simultaneously receives the row addresses from address generator 704 via address input 832 as well as disable signals via load data input 834. When the signal asserted on load data input 834 is LOW, row decoder 816 enables one of word lines 846 corresponding to each row address asserted on address input 832. When a row 814 of pixels 810 is enabled by one of word lines 846, the value of the data bit asserted on each pixel 810 by row logic 806 is latched into the associated storage element of the pixels 810 in the particular row 814. If a HIGH signal is asserted on load data input 834, row decoder 816 ignores the address asserted on address input 832 because the address received thereon corresponds to a row address of data being loaded into circular memory buffer 804.
It should be noted that for each timing signal output by timer 702, data manager 514, imager control unit 516, and imagers 504(r, g, b) process (i.e., update electrical signals on) eight rows 814 of display 808. For example, as shown in
Responsive to receiving a timing signal and row addresses, time adjuster 708 adjusts the time value output by timer 702 for the modulation period associated with each row 814 that is updated in a particular time interval. For example, in time interval 1002(0), time adjuster 708 does not adjust the time value output by timer 702 for row 814(0). For row address 814(8), time adjuster 708 decrements the time value (i.e., zero) by 8, and outputs an adjusted time value of 40. For row address 814(16), time adjuster 708 decrements the time value by 16, and outputs an adjusted time value of 32. For row address 814(24), time adjuster 708 decrements the time value by 24, and outputs an adjusted time value of 24. For row address 814(33), time adjuster 708 decrements the time value by 33, and outputs an adjusted time value of 15. For row address 814(41), time adjuster 708 decrements the time value by 418, and outputs an adjusted time value of 7. For row address 814(45), time adjuster 708 decrements the time value by 45, and outputs an adjusted time value of 3. Finally, for row address 814(47), time adjuster 708 decrements the time value by 47, and outputs an adjusted time value of 1.
It should be noted that a timing signal output by timer 702 having a value of zero (0) marks the beginning of a new modulation period for row 814(0). Accordingly, data manager 514 must provide new display data for row 814(0) to each imager 504(r, g, b) before row logic 806 can update row 814(0) for the first time in its first/next modulation period. Accordingly, data manager 514 can provide data for row 814(0) to imagers 504(r, g, b) at a variety of different times. For example, data manager 514 could provide the display data all at the beginning of time interval 1002(0) before row 814(0) is updated by imager control unit 516 and imagers 504(r, g, b). Alternately, data manager 514 could transfer the display data for row 814(0) to imagers 504(r, g, b) during (e.g., at the end of) the previous time interval 1002(47). In either case, display data for at least one of rows(0-47) should be transferred to imagers 504(r,g,b) during each time interval 1002(0-47). In the present embodiment, it will be assumed that data manager 514 loads display data for row 814(0) during time interval 1002(47) after all rows in time interval 1002(47)'s row schedule have been updated.
Because shift register 802 contains enough memory to store display data for an entire row 814 of pixels, data manager 514 can load display data for a row 814 to imagers 504(r, g, b) without being synchronized with address generator 704. Thus, the data storage provided by shift register 802 advantageously decouples the processes of providing display data to imagers 504(r, g, b) and the loading of the display data into circular memory buffer 804.
No matter what scheme for providing display data to imagers 504(r, g, b) is used, address generator 704 will assert a “write” address for each row 814 of display data provided to imagers 504(r, g, b) by data manager 514 at an appropriate time. For example, address generator 704 might sequentially assert a write address for a row 814 (e.g., row 814(0)) of display data stored in shift register 802 after all rows are processed during the preceding time interval (e.g., time interval 1002(47)). Alternately, address generator could assert each write address for the stored row 814 (e.g., row 814(0)) at the beginning of time interval (e.g., time interval 1002(0)). In either case, it is important to note that display data should be supplied to each of imagers 504(r, g, b) in the same order as the rows 814 are assigned to modulation periods. In the present embodiment, display data is supplied to imagers 504(r, g, b) in order from row 814(0) through row 814(47).
When a “write” address is asserted on address output bus 718, address generator 704 will also assert a HIGH load data signal on load data output 720, causing circular memory buffer 804 to store the display data being asserted on data lines 836 by shift register 802. In addition, the HIGH load data signal asserted on load data output 720 also temporarily disables row decoder 816 from enabling a new word line 846 associated with the write address, and prevents time adjuster 708 from altering the adjusted timing signal asserted on adjusted timing output 722.
While the displays 808 of imagers 504(r, g, b) are being modulated, debias controller 706 is coordinating the debiasing process of display 808 of each imager 504(r, g, b) by asserting data invert signals on global data invert output 726 and a plurality of common voltages on common voltage output 724. Debias controller 706 debiases display 808 of each imager 504(r, g, b) to prevent deterioration of the displays 808. Debias controller 706 debiases each display 808 by causing the electrical signals asserted on each pixel 810 to be asserted in a first bias direction during a first group of time intervals 1002(0-47), and causing the electrical signals to be asserted in a second bias direction during a second group of time intervals 1002(0-47). The bias directions are relative to the common electrode overlying each display 808.
Because the operation of data manager 514, the components of imager control unit 516, and each of imagers 504(r, g, b) is either directly or indirectly dependent upon the timing signals produced by timer 702, displays 808 in each imager 504(r, g, b) remains synchronized during the display driving process. Therefore, a coherent, full color image is formed when the images produced by displays 808 of imagers 504(r, g, b) are superimposed.
As described thus far, the present invention provides many advantages over prior art display driving systems. First, because the present invention sets the number of non-zero intensity states (i.e., grayscales) equal to an integer multiple of the number of rows in the display, data and instruction transfer from display driver 502 to imagers 504(r, g, b) (and among other elements of display system 500) is 100% efficiency over the entire frame of display data. In the example described above, the signals on eight rows are updated during each time interval. Furthermore, the fact that each row in the display is assigned to its own modulation period and driven asynchronously aids in equalizing the bandwidth. In particular, the total number of row updates can be spread over the entire frame, which becomes more and more beneficial as the number of rows and bits in compound data words increases.
The present invention also provides the advantage that the same number of rows that are assigned to particular sets (e.g., even- and odd-numbered rows) can be updated during each time interval 1002. As will be described in greater detail below, this enables different rows 814 of the display 808 to be driven by different pixel control circuitries in the same imager. Because an equal number of rows that are assigned to each set are updated during each time interval 1002, each pixel control circuitry controlling a set of rows in display 808 will be operating at 100% efficiency during each time interval 1002. In addition, driving different sets of rows 814 in display 808 with different modulation circuitries in the same imager enables the pixels 810 in display 808 to be updated more times per frame.
The present invention also facilitates writing intensity values to pixels using fewer pulse transitions than conventional pulse width modulation driving schemes. This advantageously improves the displayed image because the liquid crystal material in the pixel cell is charging and discharging fewer times per frame, thereby improving contrast, reducing visual artifacts such as ghosting, and reducing lateral field effects.
Finally, recall that the present invention is equally applicable to field-sequential display systems where a single imager sequentially processes each color of display data. If the present invention is used to drive a field-sequential display, the various components of display system and the imager may be modified as necessary. For example, circular memory buffer 806 might be modified to contain image data for each color of display data. As another example, fewer display data lines 520 between data manager 514 and the imager may be needed in a field-sequential display system. These and other modifications will become apparent in view of this disclosure of the present invention.
Read address generator 1502 receives 6-bit time values from timer 702 via timing input 716 and Vsync signals via synchronization input 714. Based on the time value, read address generator 1502 sequentially outputs row addresses that are updated during that time value onto 6-bit read address lines 1508. While read address generator is outputting read row addresses onto lines 1508, read address generator also asserts a LOW write enable signal on a write enable line 1510. Write enable line 1510 is coupled to write address generator 1504, to the control terminal of multiplexer 1508, and to load data output 720. A LOW write enable signal disables write address generator 1504, and instructs multiplexer 1506 to couple read address lines 1508 with address output bus 718, such that “read” row addresses are delivered to time adjuster 708 and to imagers 504(r, g, b).
A LOW write enable signal asserted on load data output 720 serves as a LOW load data signal for time adjuster 708, circular memory buffer 804, and row decoder 816. Accordingly, while write enable signal remains LOW, time adjuster 708 adjusts the time value generated by timer 702 for each read row address generated by read address generator 1502, circular memory buffer 804 outputs bits of display data associated with each read row address, and row decoder 816 enables word lines 846 corresponding to each read row address.
A short time after read address generator 1502 has generated a final read row address for the particular time value, read address generator 1502 asserts a HIGH write enable signal on write enable line 1510. In response, write address generator 1504 generates a “write” row address and asserts the write address on write address lines 1512 such that a new row of data can be written into circular memory buffer 804. In addition, when a HIGH write enable signal is asserted on write enable line 1510, multiplexer 1506 is operative to couple write address lines 1512 with address output bus 718, thereby delivering write addresses to time adjuster 708 and imagers 504(r, g, b). A HIGH write enable signal (i.e., a HIGH load data signal) also disables time adjuster 708 and row decoder 816, and causes circular memory buffer 804 to load a row of new display data from shift register 802 into memory locations associated with the generated write row addresses.
Write address generator 1504 also receives timing signals indicative of a time interval 1002 via timing input 716, and Vsync signals via synchronization input 714. When the write enable signal is HIGH, write address generator 1504 outputs a row address for a row 814 whose modulation period is beginning in the subsequent time interval 1002. For example, if the time value on timing input 716 was zero, corresponding to time interval 1002(0), then write address generator 1504 would generate a write row address for row 814(1). Similarly, if the time value was one, then write address generator 1504 would generate a write row address for row 814(2). As another example, if the time value was 47, then write address generator 1504 would generate a write row address for row 814(0). In this manner, rows of display data stored in shift register 802 can be written into circular memory buffer 804 before they are needed by row logic 806 to modulate display 808.
Depending on the signals asserted on the inputs of XOR gate 1704 by storage element 1702 and global data invert line 1708 (via global data invert input 824), XOR gate is operative to assert either a HIGH or a LOW driving voltage onto pixel electrode 1706. For example, if the signal asserted on data invert line 1708 is a digital HIGH, then voltage inverter 1704 asserts the inverted value of the voltage output by storage element 1702 onto pixel electrode 1706. On the other hand, if the signal asserted on data invert line 1708 is a digital LOW, then voltage inverter 1704 asserts the value of the voltage output by storage element 1702 onto pixel electrode 1706. Thus, either the data bit latched in storage element 1702 will be asserted on pixel electrode 1706 (normal state) or the inverse of the latched bit will be asserted on pixel electrode 1706 (inverted stated), depending on the signal asserted on global data invert line 1708 via global data invert input 824.
Note that pixel cells 810 are advantageously single latch cells. In addition, because the voltages applied to pixel electrodes 1706 can be inverted simply by switching the output of voltage inverter 1704 or 1710, display 808 can be easily debiased without rewriting data to pixels 810, thereby decreasing the required bandwidth as compared to the prior art.
In the embodiments shown in
Increasing the value of n increases the number of non-zero intensity values (e.g., grayscales) that that each pixel 810 in display 808 can produce. Recall that each pixel 810 can produce (nr+1) intensity values (including zero), where n is an integer greater than zero. In the previous embodiment, timer 702 generated forty-eight time values because n equaled one and r equaled forty-eight. However, in the present embodiment, timer 702 generates ninety-six (96) time values because n equals two and r equals forty-eight. In other words, by setting n equal to two, each pixel 810 can display twice as many non-zero intensity values as there are physical rows 814 in display 808.
Electrical signals corresponding to particular grayscale values are written to the pixels in each physical row 814(0-47) by row logic 806 within the row's respective modulation period. Because the number of rows 814(0-47) is only half of the number of time intervals 1902(0-95), the modulation periods of rows 814(0-47) begin during every other one of time intervals 1902(0-7) and ends after the lapse of 96 time intervals 1902 from the start of the respective modulation period. For example, row 814(0) has a modulation period that begins at the beginning of time interval 1902(0) and end after the lapse of time interval 19002(95). Similarly, row 814(1) has a modulation period that begins at the beginning of time interval 1902(2) and ends after the lapse of time interval 1902(1). Like in
Like the previous embodiment, each row 814's modulation period is temporally offset by n time intervals 1902 from the previous row's modulation period. For example, the modulation period of row 814(1) is temporally offset with respect to the modulation period of row 814(0) by two time intervals 1902. Thus, rows 814(0-47) are still driven asynchronously. In addition, as previously suggested, data can be written to pixels 810 more than once per frame by defining a frame time to include multiple modulation periods to improve the quality of the displayed image.
Like data word 602, the sum of the weighted values of bit code in data word 602A meets the constraints of the first aspect of the present invention. In particular, the sum of the weights in column 2004 add up to an integer multiple of the number of rows 814. Here, the sum of the weights in column 2004 equal ninety-six, which is two times the number of physical rows. In addition, the number of bits in the bit code in column 2004 is evenly divisible by n. In particular, there are twelve bits in the code in column 2004, which when divided by two (n=2), yields six. Therefore, the bit code of data word 602A shown in column 2004 facilitates updating the same number of rows 814 in display 808 during each time interval 1902.
The bit code of data word 602A also meets the constraints of the second aspect of the present invention. In particular, the number of bits in data word 602A (i.e., twelve bits) is evenly must be evenly divisible by 2n (i.e., four). In addition, the sum of the weighted values of the bits in compound data word 602A in column 2004 must be evenly divisible by 2n. Here, the quotient of 96 and 4 is 24. Finally, as described in more detail below, the bit code in column 2004 produces row schedules for each time interval 1902 wherein an equal number of even-numbered rows and odd-numbered rows 814 are updated during each time interval 1902. If the bit code of data word 602A meets these limitations, then both iterations of pixel control circuitry in an imager 504 will operate at 100% efficiency during each time interval 1902 because each will perform the same number of row updates.
A third column 2006 in table 2000 indicates the update time intervals 1902 during which particular bits are written the pixels 810 in each row 814 during that row's adjusted modulation period. Recall that an adjusted modulation period assumes that the row 814's modulation period begins at time interval 1902(0) and ends after time interval 1902(95). For example, B0 is written to a pixel 810 in row 814 during time interval 1902(0) (i.e., the first time interval) during that row's adjusted modulation period. Similarly, bits B1, B2, B3, B4, B5, B6, B7, B8, B9, B10, and B11 are written to the pixel 810 in time intervals 1902(1), 1902(3), 1902(7), 1902(15), 1902(26), 1902(36), 1902(45), 1902(54), 1902(64), 1902(74), and 1902(85), respectively.
In general, a particular bit in column 2002 will be written to pixel 810 in a particular row 814 during a time interval 1902(x) in that row's modulation period, where x is equal to the sum of the weights of the bits previously written to pixel 810. For example, bits B3 are written to a row of pixels 810 in time interval 1902(7) of that row 814's modulation period. Note that the sum of the weights of B0-B2 is equal to seven (i.e., 1+2+4=7). Similarly, bits B7 are written to a row of pixels 810 in time interval 1902(45), and the sum of the weights of bits B0-B6 is equal to 45 (i.e. 1+2+4+8+11+10+9=45).
A generic row schedule, from which other generic row schedules can be generated, is shown in a fourth column 2008 and is determined based on the update time intervals 1902 calculated in column 2006. The generic row schedule shown in column 2008 is calculated according to the following formula:
where n is a non-zero integer, r is the number of physical rows 814 in display 808, T_Event represents an update time interval given in column 2006, and INT is the integer function. In the present embodiment, n equals two (2), such that the above equation can be simplified to the following:
Recall that there are twice as many time intervals 1902(0-95) than there are physical rows 814(0-47). Therefore, the generic row schedule in column 2008 has to be divided in to n remainder groups, and the row schedule associated with each remainder group can then be used to generate a row schedule for each time interval 1902. This requirement also ensures that an equal number of rows 814 are updated during each time interval 1902. Accordingly, the row schedule in column 2008 is divided into n remainder groups according to the following formula:
Remainder Group=((nr)−T_Event)% n,
where % is the remainder function.
A fifth column 2010 shows the remainder groups and their associated generic row schedules. From these generic row schedules, the row schedule for each time interval 1902(0-95) can be calculated based on a time interval's affiliation with a particular remainder group. As shown in columns 2010 and 2008, the generic row schedule for remainder group zero includes rows 814(0), 814(35), 814(30), 814(21), 814(16), and 814(11). The generic row schedule for remainder group one includes rows 814(47), 814(46), 814(44), 814(40), 814(25), and 814(5).
At this point, it is known that the bit code of data word 602A meets the constraints for both aspects of the present invention described above. In particular, each remainder group in column 2010 has an equal number of rows (i.e., six) assigned to it from the generic row schedule in column 2008. Therefore, six rows 814 will be updated during each time interval 1902(0-95). The bit code of data word 602A also produces generic row schedules that are even and odd balanced. Note from columns 2008 and 2010 that an equal number of even- and odd-numbered rows are assigned to each remainder group 0 and 1. This ensures that, if a display 808 is driven with two iterations of pixel control circuitry (one for odd-numbered and one for even-numbered rows), each pixel control circuitry will operate at 100% efficiency (i.e., update the same number of rows) during each time interval 1902(0-95).
The counter value is added to the generic row schedule for remainder group zero in column 2104 to adjust the row schedule for a particular physical row 814's modulation period. The counter value is constrained by the number of physical rows 814, so in the present embodiment the counter steps through values between zero (0) and forty-seven (47). In addition, the counter steps through each count value n times. Accordingly, where n=2, the counter outputs values ranging from 0 to 47 in the following pattern: 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, . . . , 46, 46, 47, 47, 0. Note that the counter begins and ends at the same value.
Based on
Note again that (b/n) rows 814 are updated during each time interval 1902. In the present embodiment, b (the number of bits in data word 602A) equals 12, and n equals 2 such that six rows 814 are updated during each time interval 1902. In addition, row logic 806 updates an equal number (i.e., three) of even and odd rows during each time interval 1902. Thus, data transfer from the display system to the imager(s) is 100% efficient during each time interval. In addition, if the imager includes two iterations of pixel control circuitry (one for even-numbered and one for odd-numbered rows), then each pixel control circuitry can also operate at 100% efficiency during each time interval.
Chart 2200 indicates when particular bits of data word 602A are written to a particular row 814 of pixels during that pixel's modulation period (i.e., by reading across a row in chart 2200). For example, row logic 806 writes bit B0 to row 814(0) during time interval 1902(0), bit B1 during time interval 1902(1), bit B2 during time interval 1902(3), bit B3 during time interval 1902(7), bit B4 during time interval 1902(15) and so on. Note, with reference to
In general, the row schedule for each time interval 1902 is calculated from the generic row schedule associated with one of the n remainder groups (such as the remainder groups in column 2010). Accordingly, each time interval 1902 is associated with one of the n remainder groups. In the embodiment shown in
Furthermore, as noted above, because an equal number of bits in data word 602A are associated with each of the n remainder groups, each row 814 will be updated during an equal number of time intervals 1902 that are associated with each of the n remainder groups in that row's modulation period. In particular, each row 814 will be updated during (b/n) time intervals 1902 that are associated with each remainder group in the row's modulation period, where b represents the number of bits in data word 602A. In addition, because each row 814's modulation period consists of the same number of time intervals 1902, each row 814 will be updated during an equal number of time intervals 1902 associated with each remainder group regardless of the modulation period's temporal offset from row 814(0)'s modulation period.
Note again that row logic 806 updates the remaining rows 814(1-47) in the same time intervals 1902(0-47) as row 814(0) when the time intervals 1902(0-47) are adjusted for a particular row's modulation period. For example, row 814(1) has a modulation period that is offset by two time intervals 1902 from row 814(0)'s modulation period. Accordingly, adding two to each update time interval 1902 associated with row 814(0) yields row 814(1)'s modulation period. In particular, row logic 806 writes B0 to row 814(1) during time interval 1902(2), B1 to row 814(1) during time interval 1902(3), B2 to row 814(1) during time interval 1902(5), B3 to row 814(1) during time interval 1902(79), B4 to row 814(1) during time interval 1902(17), etc. In other words, rows 814(0-47) are updated at different times when viewed with respect to one particular row's (i.e., row 814(0)) modulation period, however each row 814(0-47) is updated according to the same algorithm. The algorithm just starts at a different time for each row 814(0-47).
Row logic 806 and row decoder 816 update each row 814(0-47) a predetermined number of times during the row's respective modulation period. In particular, row logic 806 and row decoder 816 will update a row 814 twelve times because compound data word 602A contains twelve bits. Like in the previous embodiment, based on the adjusted time value, each logic unit 902(0-1951) in row logic 806 selects the appropriate bit of data word 602A to assert on each pixel 810 during the particular time interval 1902 via a respective one of data lines 844(0-1951).
Chart 2200 also indicates the rows 814(0-47) that row logic 806 updates in any one given time interval 1902(0-95) and the bit plane transferred to each row during the particular time interval 1902. In other words, chart 2200 graphically represents the row schedules calculated in
In addition to row logic 806, the other components of display driver 502 are modified to conform to the current embodiment of the present invention. For example, time adjuster 708 decrements time values according to the present modulation scheme and outputs only twelve different adjusted time values, which are equal to the update time intervals in column 2006.
Additionally, in the present embodiment, circular memory buffer 804 would include twelve memory sections, one for each of bits B0-B11. Based on the values of column 2006, each bit of a data word 602A can be discarded after the lapse of the following time intervals 1902:
Accordingly, for each column 812 in display 808, at least the following amounts of memory in circular memory buffer 804 are needed:
Therefore, according to the present embodiment, circular memory buffer 804 contains 823.7 kilobits of memory. In contrast, if circular memory buffer 804 was a prior-art frame buffer that stored 12 bits of video data for each pixel for the entire frame, it would contain 1.124 megabits of data. Like before, the above values assume that one row 814 of video data is written to circular memory buffer 804 during each time interval. Because there are more memory sections in circular memory buffer 804, address converter 818 is also modified to generate memory addresses for the twelve memory sections based on the same algorithms described previously. The number of address lines in address input 842 is increased accordingly.
Read address generator 2302 receives 6-bit time values from timer 702 via timing input 716, Vsync signals via synchronization input 714, and counter values from counter 2308. Based on the time value and counter value, read address generator 2302 sequentially outputs row addresses onto 6-bit read address lines 2310 that are updated during the time interval 1902. While read address generator 2302 is outputting read row addresses onto lines 2310, read address generator 2302 also asserts a LOW write enable signal on a write enable line 2312. A LOW write enable signal disables write address generator 2304, and instructs multiplexer 2306 to couple read address lines 2310 with address output bus 718, such that “read” row addresses are delivered to time adjuster 708 and to imagers 504(r, g, b). A LOW write enable signal affects time adjuster 708, circular memory buffer 804, and row decoder 816 as described in previous embodiments.
Counter 2308 receives time values from timing input 716 and Vsync signals via synchronization input 714, generates a count sequence based on the time values received, and outputs the count sequence on 6-bit count lines 2314. In the present embodiment, counter 2308 generates a count sequence from 0 to r, counting through each value n times. As described in
When read address generator 2302 receives a timing value and a count value, read address generator 2302 first determines if the timing value is associated with remainder group zero or remainder group one. Note that in
A short time after read address generator 2302 has generated a final read row address for the particular time interval 1902, read address generator 2302 asserts a HIGH write enable signal on write enable line 2312. In response, write address generator 2304 generates a “write” row address and asserts the write address on write address lines 2316 such that a new row of data can be written into circular memory buffer 804. In addition, when a HIGH write enable signal is asserted on write enable line 2312, multiplexer 2306 is operative to couple write address lines 2316 with address output bus 718, thereby delivering write addresses to time adjuster 708 and imagers 504(r, g, b). A HIGH write enable signal (i.e., a HIGH load data signal) also disables time adjuster 708 and row decoder 816, and causes circular memory buffer 804 to load a row of new display data from shift register 802 into memory locations associated with the generated write row addresses.
Write address generator 2304 also receives timing signals indicative of a time interval 1902 via timing input 716, and Vsync signals via synchronization input 714. When the write enable signal is HIGH, write address generator 2304 outputs a row address for a row 814 whose modulation period is beginning in one of the next two time intervals 1902. For example, if the timing signal received via timing input 716 had a value of 0 or 1, corresponding to time intervals 1902(0) or 1902(1), then write address generator 2304 would generate row addresses for the row 814(1). Similarly, if the timing signal had a value of 2 or 3 indicative of time interval 1902(2) or 1902(3), then write address generator 1504 would generate a row address for row 814(2). As another example, if the timing signal had a value of 94 or 95, then write address generator 1504 would generate a row address for row 814(0). Note that because new rows of data are needed only every second time interval 1902 (see
Based on
Based on the bit code in column 2004, B0 can only jump (clockwise) from first quadrant 2502 to second quadrant 2504 because bit B0 has a weight of one. B0, therefore, lands in second quadrant 2504. Next, bit B1, which has a weight of two, begins jumping clockwise from second quadrant 2504 because that is where bit B0 landed. Bit B1 jumps through third quadrant and into fourth quadrant 2508, where it lands. Next, bit B2, which has a weigh of four time intervals 1902, takes four jumps clockwise starting in fourth quadrant 2508 and lands back in fourth quadrant 2508. This process continues for the remaining bits B3-B11.
Because three bits have landed in each quadrant, it is known that the bit code shown in column 2004 will yields two generic row schedules, each containing an equal number of rows where half of the rows are even-numbered and half or the rows are odd-numbered.
Display system 2600 also includes a global timing control unit 2612 that asserts clock signals and operational instructions on a global control bus 2613 to control and coordinate the operation of display driver 2602, imagers 2604(r, g, and b) and frame buffers 2606(A and B). Timing control unit 2612 provides the same functions and advantages as timing control unit 512 including spreading unused frame time over the entire frame and between at least some time intervals. Again, bus 2613 communication with all elements of display system 2600 but is only represented generally so as not to unnecessarily obscure the other aspects of the present invention.
Display driver 2602 includes a data manager 2614 and an imager control unit (ICU) 2616, which are both coupled to the various components of display system 2600 like data manager 514 and ICU 516 of display system 500. However, in the present embodiment, data manager 2614 receives 33-bit binary video data (11 bits per color) via video data input terminal set 2610, separates the video data according to color, converts the binary video data into binary-coded and thermometer-coded video data and provides the compound video data to one of frame buffers 2606(A-B) via 384-bit buffer data bus 2618. Buffer data bus 2618 is substantially larger than buffer data bus 518 because data manager 2614 converts the 11-bit binary display data into compound display data having substantially more bits. Data manager 2614 also retrieves video data from one of frame buffers 2606(A-B), and provides each color (i.e., red, green, and blue) of video data to the respective imager 2604(r, g, b) via imager data lines 2620(r, g, b). Note that imager data lines 2620 (r, g, b) each include 64 lines. As will be described later, each pixel is driven with compound data words having 32 bits consisting of both binary- and thermometer-coded bits. Therefore, two pixels worth of data can be transferred at once to each imager 2604(r, g, b) via data lines 2620(r, g, b). Finally, because of the increased number of rows in imagers ICU 2605(r, g, b), ICU 2616 controls imagers 2604(r, g, and b) via 25 common imager control lines 2624 such that imagers 2604(r, g, and b) modulate each pixel of their respective displays according to the video data supplied by data manager 2614.
Like prior embodiments, the pixels of imagers 2604(r, g, b) are modulated with a reduced number of pulses than in a conventional pulse width modulation scheme. In addition, each row of pixels of imagers 2604(r, g, b) are driven asynchronously such that the rows are processed during distinct modulation periods that are temporally offset. Furthermore, each modulation period is divided into a plurality of time intervals such that a constant number of rows are updated during each time interval. These and other advantageous aspects of the present invention will be described in further detail below.
Like
According to one aspect of the present invention, data manager 2614 converts 11-bit binary video data for each pixel in each imager 2604(r, g, b) into a data word 2702 subject to the following limitations. In particular, data manager 2614 converts each binary-weighted data word into a compound data word 2702 wherein the sum of the weighted values of the binary-coded bits 2704 and the thermometer-coded bits 2706 is equal to an integer multiple (n) of the number of rows of pixels in one of imagers 2604(r, g, b). In the present embodiment, n is equal to one again, and the number of rows in each imager 2604(r, g, b) is 1112. Therefore, the sum of the weighted values of the bits in each combination data word 2702 should equal 1112. A second requirement for this aspect of the present invention is that the number of bits, b, in the bit code of data word 2702 is evenly divisible by n. Because n equals one in this embodiment, this limitation is met. By setting the number of non-zero intensity values that can be defined by a compound data word 2702 equal to an integer multiple of the number of rows in the imager's display, an equal number of rows in the display can be updated during each time interval. This facilitates 100% data efficiency between the display driver 2602 and each imager 2604(r, g, b).
According to a more particular aspect of the present invention, an imager 2604 can include a plurality of pixel control circuitries, each controlling the modulation of a set of rows in the display. To facilitate 100% operating efficiency of each pixel control circuitry in the imager, each pixel control circuitry must update the same number of rows in that single imager during each time interval. To ensure this result, data manager 2614 converts binary data words into compound data words 2702 according to the following additional limitations. First, the number of bits in the bit code of compound data word 2702 must be evenly divisible by (s*n), where s is the number of pixel control circuitries in each imager. Second, the sum of the weighted values of the bits in the bit code of compound data word 2702 must be evenly divisible by (s*n). Finally, an equal number of rows in the display assigned to each of the (s) sets must be updated during each time interval.
Assigning each row of pixels in the display in imagers 2604(r, g, b) to one of two sets (i.e., s=2) provides a useful example. Again, the even-numbered rows in a display can be assigned to one set and the odd-numbered rows in the display can be assigned to a second set. According to this example, data manager 2614 converts binary data words into compound data words 2702 having a number of bits evenly divisible by 2n. In addition, the sum of the weighted values of the bits in each data word 2702 is evenly divisible by 2n. Finally, the bit code of data words 2702 must produce row update schedules for each time interval wherein an equal number of even- and odd-numbered rows are updated during each time interval.
As before, the number of bits and weighted values of each bit in combination data word 2702 are completely arbitrary so long as the above limitations are satisfied.
When data manager 2614 receives 11 bits of binary video data for a particular pixel, data manager determines what intensity value the data represents, and then converts the 11-bit data word into a compound data word 2702 corresponding to the same grayscale value. Each of the binary-coded bits 2704 and thermometer-coded bits 2706 in a data word 2702 are assigned a digital ON of OFF value such that the electrical signal written to a particular pixel will experience a number of signal transitions (i.e., pulses) that is less than or equal to the amount of signal transitions experienced in conventional pulse-width modulation such as described in
Data manager 2614 also retrieves data from frame buffers 2606(A-B) and provides that data to imagers 2604(r, g, b) via imager data lines 2620(r, g, b) where the data is temporarily stored. Data manager 2614 provides the data words 2702 for each pixel to imagers 2604(r, g, b) before they are needed to drive electrical signals on the particular pixels in imagers 2604(r, g, b).
For instance, timer 2802 coordinates the operations of the various components of imager control unit 2616 by generating a sequence of n*r time values, where n is an integer greater than zero and r equals the number of rows of pixels in imagers 2604(r, g, b). In the present embodiment, timer 2802 outputs consecutive time values from 0 to 1111 because n is equal to 1 and r is equal to 1112. Once timer 2802 reaches a value of 1111, timer 2802 loops back such that the next timing signal output has a value of 0. Timer 2802 asserts each time value on 11-bit time value output bus 2812, which provides the timing signals to coordination line 2622, address generator 2804, debias controller 2806, and time adjuster 2808.
Like address generator 704, responsive to timing signals on timing input 2816, address generator 2804 provides row addresses to each of imagers 2604(r, g, b) and to time adjuster 2808 via an 11-bit address output bus 2818. In the present embodiment, address generator 2804 generates 11-bit row addresses and asserts each bit of the generated row addresses on a respective line of address output bus 2818. Furthermore, depending on whether the row address generated by address generator 2804 is a “read” address (e.g., to read data from display memory) or a “write” address (e.g., to write data to display memory), address generator 2804 will assert a load data signal on load data output 2820. In the present embodiment, a digital LOW value asserted on load data output 2820 indicates that address generator 2804 is asserting a read address while a digital HIGH value indicates a write address.
Time adjuster 2808 adjusts the time value output by timer 2802 depending on the row address asserted on address output bus 2818. Time adjuster 2808 receives 11-bit time values from bus 2812, load data signals from load data output 2820, and 11-bit row addresses from address output bus 2818. Responsive to the signal asserted on load data output 2820 and the row address asserted on address output bus 2818, time adjuster 2808 adjusts the time values asserted on time value output bus 2812 and asserts the adjusted time value on adjusted timing output bus 2822. Again, time adjuster 2808 adjusts time values asserted on bus 2812 only for read row addresses (i.e., when the load data signal on output 2820 is LOW).
Debias controller 2806 controls the debiasing process of each of imagers 504(r, g, b) in order to prevent deterioration of the liquid crystal material therein. Debias controller 2806 is coupled to time value output bus 2812 and includes a common voltage output 2824 and a global data invert output 2826. Debias controller 2806 receives timing signals from timer 2802 via bus 2812, and depending on the value of the timing signal, asserts one of a plurality of predetermined voltages on common voltage output 2824 and a HIGH or LOW global data invert signal on global data invert output 2826. The voltage asserted by debias controller 2806 on common voltage output 2824 is asserted on the common electrode (e.g., an Indium-Tin Oxide (ITO) layer) of the pixel array of each of imagers 2604(r, g, b). In addition, the global data invert signals asserted on global data invert output 2826 determine whether data asserted on each of the electrodes of the pixel cells of imagers 2604(r, g, b) is asserted in a normal or inverted state.
Finally, the 25 imager control lines 2828 convey the outputs of the various elements of imager control unit 2616 to each of imagers 2604(r, g, b). In particular, imager control lines 2828 include address output bus 2818 (11 lines), load data output 2820 (1 line), adjusted timing output bus 2822 (11 lines), common voltage output 2824 (1 line), and global data invert output 2826 (1 line). Each of imagers 2604(r, g, b) receive the same signals from imager control unit 2616 such that imagers 2604(r, g, b) remain synchronized.
Shift register 2902 receives and temporarily stores display data for a single row 2914 of pixel cells 2910 of display 2908. Display data is written into shift register 2902 64 bits at a time via data input 2922 until display data for a complete row 2914 has been received and stored. Shift register 2902 receives two pixels worth of video data at a time and is large enough to store 32 bits (i.e., one combination data word 2902) of video data for each pixel cell 2910 in a row 2914. Once shift register 2902 contains data for a complete row 2914 of pixel cells 2910, the data transferred from shift register 2902 into circular memory buffer 2904 via data lines 2936 (1952×32).
Circular memory buffer 2904 receives rows of 32-bit display data output by shift register 2902 on data lines 2936, and stores the video data for an amount of time sufficient for a signal corresponding to grayscale value of the data to be asserted on an appropriate pixel 2910 of display 2908. Responsive to control signals, circular memory buffer 2904 asserts the 32-bit display data associated with each pixel 2910 of a row 2914 of display 2908 onto data lines 2938 (1952×32). To control the input and output of data, circular memory buffer 2904 includes a single bit load input 2940 and a 272-bit address input 2942. Responsive to HIGH signal on load input 2940, circular memory buffer 2904 loads the bits of video data asserted on data lines 2936 into memory. Responsive to a LOW signal, circular memory buffer retrieves a row of compound video data words 2702 from memory and asserts the data onto data lines 2938. Address converter 2918 determines the memory locations that display data bits are written to or read from.
Row logic 2906 writes single bits of data to the pixels 2910 of display 2908 depending on the adjusted time value received on adjusted timing input 2930. Row logic 2906 receives an entire row of 32-bit combination display data via data lines 2938 for each pixel in a row 2914, and based on the display data and adjusted time value, updates the single bits asserted on pixels 2910 of the particular row 2914 via display data lines 2944. Like row logic 806, row logic 2908 updates the electrical signals asserted on each pixel 2910 in a row 814(0-1111) for each read row address asserted by address generator 2804. Based on the display data and adjusted time value, row logic 2906 writes the appropriate bit of combination data word 2702 at the appropriate time such that the intensity value defined by combination data word 2702 is asserted on the appropriate pixel 2914.
Display 808 has 1952 columns 2912 and 1112 rows 2914 of pixel cells 2910. Each row 2914 is enabled by an associated one of a plurality of word lines 2946. Because display 2908 includes 1112 rows of pixels 2910, there are 1112 word lines 2946. In addition, one data line 2944 communicates data between row logic 2906 and each column 2912 of display 2908 to an enabled pixel 2910 in the particular column.
Display 2908 also includes a common electrode (e.g., an Indium-Tin-Oxide layer, not shown) overlying all of pixels 2910. Voltages can be asserted on the common electrode via common voltage input 2926. In addition, the voltage asserted on each pixel 2910 by the single bit stored therein can be inverted (i.e., switched between normal and inverted values) depending upon the signal asserted on global data invert input 2924. The signal asserted on global data invert input 2924 is provided to each pixel cell 2910 of display 2908. The signals asserted on global data invert terminal 824 and the voltages asserted on common voltage input 826 are used to debias display 808.
Row decoder 2916 asserts a signal on one of word lines 2946 at a time, such that the single bit data asserted by row logic 2906 on display lines 2944 is latched into the enabled row 2914 of pixels 2908. Like row decoder 816, when the signal asserted on load data input 2934 is a digital HIGH, then row decoder 2916 ignores the row address asserted on address input 2932 and does not enable a new one of word lines 2946.
It should be noted that the large number of lines between some of the components of imager 2604(r, g, b) will be reduced in practice. Indeed, as is well known in the art, large amounts of data can be transferred between electronic components over several clock cycles in order to reduce the bandwidth between those components. However, for the sake of clarity, imager 2604(r, g, b) is described with a large number of data lines between some of its components.
Like in imager 504(r, g, b), the components of imager 2604(r, g, b), other than display 2908, comprises the pixel control circuitry that carries out the modulation of display 2908. Similarly, imager 2604(r, g, b) can include multiple pixel control circuitries where each pixel control circuitry is responsible for modulating a defined set of rows in display 2908. This advantageously reduces the number of operations that one pixel control circuitry would have to perform. In other words, multiple pixel control circuitries can update the electrical signals on pixels more times per frame than one pixel control circuitry alone.
Like row logic 806, row logic 2906 asserts electrical signals corresponding to a particular intensity value within a row 2914's modulation period. Because the number of rows 2914(0-1111) is equal to the number of time intervals 3002(0-1111), each row 2914(0-1111) has a modulation period that begins in one of time intervals 3002(0-1111) and ends after the lapse of 1111 time intervals 3002(0-1111) thereafter. The beginning of each row 2914's modulation period is indicated in
Like in modulation scheme 1000 shown in
Each bit in column 3102 has a corresponding weight, which is given in a second column 3104 in the respective row. Column 3104 indicates the bit code for the data words 2702 and each bit weight is given in a number of time intervals 3002.
A third column 3106 indicates an update schedule for a particular row based on the bit code in column 3104 during that row's adjusted modulation period. In particular, a bit in column 3102 is written to each pixel in the particular row during the associated update time interval (“T_Event”) in column 3106 during that pixel's adjusted modulation period. Note that the update time intervals 3002 in column 3106 assume that the row's modulation period begins in time interval 3002(0) and ends after time interval 3002(1111). For example, row logic 2906 writes a B0 bit to each pixel in the row during time interval 3002(0) in that row's modulation period. Similarly, row logic 2906 writes bits B1, B2, . . . , B15, B16, . . . , B29, B30, and B31 to each pixel 2910 in the row during time intervals 3002(1), 3002(3), . . . , 3002(508), 31002(544), . . . , 3002(1009), 3002(1043), and 3002(1078), respectively, in that row's modulation period.
In general, a particular bit in column 3102 will be written to pixels in a row during a time interval 3002(x) in that row's modulation period, where x equals the sum of the weights of the bits previously written to pixel 2910. For example, bit B3 is written to pixel 810 in time interval 3002(7). Note that the sum of the weights of bits B0-B2 is equal to 7 (i.e., 1+2+4=7). Similarly, bit B31 is written to pixel 2910 in time interval 3002(1078), and the sum of the weights of bits B0-B30 is equal to 1078 (i.e. 1+2+4+8+ . . . +34+35+34+35=1078).
Recall that the bit code in column 3104 is completely arbitrary as long as it meets the constraints set forth above in
A fourth column 3108 shows a generic row schedule for determining the row schedule for each of time intervals 3002(0-1111). The row schedule for each time interval 3002(0-1111) can be determined by the following formula:
Row=(r−T_event)+τ,
where “Row” denotes the row that will be updated, r represents the total number of rows in display 2908, T_event represents the update time interval 3002 for a particular bit in column 3106, and τ is the number of the time interval 3002(0-1111) that the row schedule is being calculated for. Note that τ is an integer in the range of zero to 1111. Therefore, when subtracting or adding in the above equation, the value of Row should not go negative or above 1111, but should loop forward or backward to a row value between 0 and 1111, inclusive. The formula is repeated for each bit in data word 2702 for each time interval 3002.
Because τ=0 for time interval 3002(0), column 3108 indicates the row schedule for time interval 3002(0). Note that the row schedules for the remaining time intervals 3002(1-1111) can also be calculated by incrementing the values in column 3108 by a number of rows equal to the time interval number. For example, the row schedule for time interval 3002(1) can be calculated by adding one to each row value in column 3108. Similarly, the row schedule for time interval 3002(2) can be calculated by adding two to each row value in column 3108. Note that a row value of 1112 is equivalent to a row value of zero and is indicative of row 2914(0). Accordingly, the next row value after 1112 is row value 1. This process yields the same row update schedule for a particular time interval as the formula given above.
The generic row schedule in column 3108 also enables an equal number of even- and odd-numbered rows 2914 to be updated during each time interval 3002(0-1111). Columns 3110 and 3112 indicate with an “X” whether a particular row in column 3108 is even or odd. Note that there are 16 even and odd rows that are updated during each time interval 3002(0-1111).
Increasing the value of n increases the number of intensity values (e.g., grayscales) that that each pixel 2910 in display 2908 can produce. Recall that each pixel 2910 can produce (nr+1) intensity values (including zero), where n is a non-zero integer because there are n*r time intervals. In the previous embodiment, timer 2802 generated 1112 time values because n equaled one and r equaled 1112. However, in the present embodiment, timer 2802 generates 2224 time values because n*r (i.e., 2*1112) equals 2224.
Row logic 2906 writes electrical signals corresponding to particular intensity values to the pixels in each physical row 2914(0-1111) within the row's respective modulation period. Because the number of rows 2914(0-1111) is only half of the number of time intervals 3302(0-2223), the modulation periods of rows 2914(0-1111) begin during every other one of time intervals 3302(0-2223) and end after the lapse of 2223 time intervals thereafter. For example, row 2914(0) has a modulation period that begins at the beginning of time interval 3302(0) and end after the lapse of time interval 3302(2223). Similarly, row 2914(1) has a modulation period that begins at the beginning of time interval 3302(2) and ends after the lapse of time interval 3302(1). Again, the beginning of each row 2914's modulation period is indicated in
Like the previous embodiment, each row 2914's modulation period is temporally offset by n time intervals 1902 from the previous row's modulation period. For example, row 2914(1)'s modulation period is temporally offset from row 2914(0)'s modulation period by two time intervals 3302. Thus, rows 2914(0-1111) are still driven asynchronously. In addition, as previously suggested, multiple modulation periods can be defined in each frame to improve the quality of the displayed image.
Like data word 2702, the sum of the weighted values of bit code in data word 2702A meets the constraints of the first aspect of the present invention. In particular, the sum of the weights in column 3404 add up to an integer multiple of the number of rows 2914. Here, the sum of the weights in column 2404 equal 2224, which is two times the number of physical rows 2914 in display 2908. In addition, the number of bits in the bit code in column 3404 is evenly divisible by n. In particular, there are thirty-two bits in the code in column 3404, which when divided by two (i.e., n=2), yields sixteen. Therefore, the bit code of data word 2702A shown in column 3404 facilitates updating the same number of rows 2914 in display 2908 during each time interval 1902.
The bit code of data word 2702A also meets the constraints of the second aspect of the present invention for s equals two (s=2). In particular, the number of bits in data word 2702A (i.e., thirty-two bits) must be evenly divisible by 2n (four for n=2). In addition, the sum of the weighted values of the bits in compound data word 2702A in column 3404 must be evenly divisible by 2n. Here, the quotient of 2224 and 4 is 556. Finally, as described in more detail below, the bit code in column 3404 produces row schedules for each time interval 3302 wherein an equal number of even- and odd-numbered rows 2914 are updated during each time interval 1902. If the bit code of data word 602A meets these limitations and an imager contains two iterations of pixel control circuitry, then both iterations of pixel control circuitry will operate at 100% efficiency during each time interval 3302(0-2223) because an equal number of even- and odd-numbered rows 2914 will be updated during each time interval 3302(0-2223).
Again, note that the number of bits and their respective weights in data word 2702A are completely arbitrary as long as constraints pertaining to the particular aspect(s) of the present invention are met.
The third column 3406 in table 3400 indicates the update time intervals 3302 during which particular bits are written to the pixels 2910 in each row 2914 during that row's adjusted modulation period. Recall that an adjusted modulation period assumes that the row 814's modulation period begins at time interval 3302(0) and ends after time interval 3302(2223). For example, B0 is written to a pixel 2910 in row 2914 during time interval 3302(0) (i.e., the first time interval) during that row's adjusted modulation period. Similarly, bits B1, B2, . . . , B15, B16, . . . , B29, B30, and B31 are written to the pixel 2910 in time intervals 3302(1), 3302(3), . . . , 3302(842), 3302(924), . . . , 3302(1981), 3302(2062), and 3302(2143), respectively. In general, a particular bit in column 3402 will be written to pixel 2910 in a particular row 2914 during a time interval 3302(x) in that row's modulation period, where x is equal to the sum of the weights of the bits previously written to the pixels 2910 in that row 2914.
A generic row schedule, from which other row schedules can be determined, is shown in a fourth column 3408 and is generated based on the update time intervals 3302 calculated in column 3406. The generic row schedule shown in column 3408 is calculated according to the following formula:
where n is a non-zero integer, r is the number of physical rows 2914 in display 2908, T_Event represents an update time interval given in column 3406, and INT is the integer function. In the present embodiment, n equals two such that the above equation can be simplified to the following:
Recall that there are twice as many time intervals 3302(0-2223) than there are rows 2914(0-1111). Therefore, the generic row schedule in column 3408 has to be divided between two time intervals. Therefore, each row in column 3408 can be assigned to one of n remainder groups, and each remainder group can be used to generate a row schedule for a time interval 3302(0-2223). Ideally, an equal number of rows 2914 are assigned to each remainder group such that an equal number of rows 2914 are updated during each time interval 3302.
Accordingly, each row in the row schedule in column 3408 is assigned to one of n remainder groups according to the following formula:
Remainder Group=((nr)−T_Event)% n,
where % is the remainder function.
A fifth column 3410 shows the two remainder groups that each of the rows in column 3408 is be assigned to according to the above formula. Fifth column 3410 shows that each remainder group (e.g., remainder group 0 and remainder group 1) contains an equal number (e.g., sixteen) of the rows in column 3408. The rows in column 3408 that are assigned to remainder group zero in column 3410 form a generic row schedule for remainder group zero. Similarly, the rows in column 3408 that are assigned to remainder group one for a generic row schedule for remainder group one.
It is important to note at this point that the generic row schedules for each remainder group contains an equal number of rows that are even and odd. Accordingly, if imager 2604 contains two iterations of pixel control circuitry, one controlling even-numbered rows and one controlling odd-numbered rows, then each iteration of pixel control circuitry will operate at 100% efficiency during each time interval 3302(0-2223).
The counter value is added to the generic row schedule for remainder group zero in column 3504 to adjust the row schedule for a particular physical row 2914's modulation period. Because there are n times as many time intervals 3302 as there are physical rows 2914, the counter steps through each count value n times. The count values produced by the counter are limited by the number of rows 2914 in display 2908. In the present embodiment, where n=2, the counter outputs values ranging from 0 to 1111 in the following sequence: 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, . . . , 1110, 1110, 1111, 1111, 0.
Based on table 3502, during time interval 3302(0), row logic writes bit B0 to each pixel in row 2914(0), bit B9 to each pixel in row 2914(943), bit B10 to each pixel in row 2914(902), bit B12 to each pixel in row 2914(817), bit B13 to each pixel in row 2914(776), and so on.
It should be noted again that each time interval 3302(0-2223) is associated with one of the n remainder groups because the row schedule for each time interval 3302 is calculated based on a generic row schedule for a particular remainder group. Accordingly, because an equal number of bits in data word 2702A are associated with each of the n remainder groups, each row 2914 will be updated during an equal number of time intervals 3302 that are associated with each of the n remainder groups. In particular, each row 2914 will be updated during (b/n) ones of the time intervals 3302 that are associated with each remainder group, where b represents the number of bits in data word 2702A. Furthermore, because each row 2914's modulation period consists of the same number of time intervals 3302, each row 814 will be updated during an equal number of time intervals 3302 associated with each remainder group regardless of the number of time intervals 3302 that the particular row's modulation period is temporally offset from row 814(0).
Quadrant-based diagram 3600 includes, in a clock-wise manner, a first quadrant 3602, a second quadrant 3604, a third quadrant 3606, and a fourth quadrant 3608. If the update schedule is balanced, each quadrant will contain eight data bits (i.e., 32 bits/4 quadrants=8 bits/quadrant). Each bit, starting consecutively with the least significant bit B0, in data word 2702A, “jumps” clockwise through a number of quadrants equal to its weight. Bit B0 starts in quadrant 3602, and each subsequent bit starts “jumping” where the previous bit “landed.” Based on the bit code for data words 2702A, eight bits have landed in each quadrant, signaling that the bit code for data word 2702 produces a balanced update schedule.
Electrical signals corresponding to particular intensity values are written to the pixels in each row 814(0-47) within the row's respective modulation period. Because in the present embodiment there are fewer time intervals 3702(0-23) than rows 814(0-47), the modulation period associated with m rows 814 will begin during each time interval 3702(0-23). For example, two rows 814(0) and 814(1) begin their modulation period in time interval 3702(0) and end their modulation period after the lapse of time interval 3702(23). Similarly, two rows 814(2) and 814(3) begin their modulation period in time interval 3702(1) and end their modulation period after the lapse of time interval 3702(0). In general, the beginning of each row 814's modulation period begins in a time interval 3702 where a “0” is indicated for that row in chart 3700. Note that the modulation period associated with a row 814 forms a frame time for that row.
Similar to other embodiments, the modulation periods for various rows 814(0-47) are temporally offset from other rows 814(0-47). For example, the modulation periods associated with rows 814(0) and 814(1) are temporally offset with respect to the modulation periods associated with every other row 814. Similarly, the modulation periods associated with rows 814(2) and 814(3) are temporally offset from with respect to the modulation periods associated with every other row 814. Thus, the rows of the display are driven asynchronously. Note that in the present embodiment, at least one modulation period begins in each time interval 3702(0-23).
Note that the bit code in column 3810 for each data word 3802 is completely arbitrary (as to the number of bits and their respective weights), except that it is subject to some limitations depending on the aspect of the invention that is implemented. According to one aspect of the present invention, the sum of the weights in column 3810 must add up to the quotient of the number of rows 814 in display 808 divided by the divisor (m). In the present embodiment, the sum of the weights in column 3810 add up to twenty-four, which is equal to quotient of forty-eight and two, where the number of rows 814 in display 808 is forty-eight and (m) equals two. This limitation on the bit code in column 3810 ensures that an equal number of rows are updated during each time interval 3702. Accordingly, the data and instruction transfer efficiency between display driver 502 and imagers 504(r, g, b) is 100% during each time interval 3702(0-23).
The bit code in column 3810 is subject to additional limitations to conform with another aspect of the present invention where each imager 504(r, g, b) includes a plurality of pixel control circuitries where each circuitry drives various sets of rows 814 in display 808. For example, where each imager 504(r, g, b) contains (s) iterations of pixel control circuitry, then the bit code in column 3810 must meet these additional limitations. First, the number of bits in the code must be divisible by (s). Second, the sum of the weighted values in column 3810 must be divisible by (s). Finally, an equal number of rows 814 belonging to each of the (s) sets of rows must be updated during each time interval 3702. These limitations ensure that an equal number of rows 814 are updated by each iteration of pixel control circuitry during each time interval 3702(0-23) such that each iteration of pixel control circuitry operates at 100% efficiency during each time interval 3702(0-23).
The bit code shown in column 3810 meets all these additional limitations as well. For example, the number of bits (six) in the bit code is divisible by two (m equals two). In addition, the sum of the weights of the bit code in column 3810 is also evenly divisible by two (i.e., 24/2=12). Finally, as will be described below, an equal number of rows assigned to each of two sets are updated during each time interval 3702(0-23).
A third column 3812 indicates an update schedule for a row 814 based on data word 3802's bit code. In particular, a bit in column 3808 is written to a particular pixel 810 during the update time interval 3702 in column 3812 in that pixel's adjusted modulation period. In this example, B0 is written to a pixel 810 during time interval 3702(0) in that pixel's modulation period. Similarly, bits B1, B2, B3, B4, and B5, are written to pixel 810 in time intervals 3702(1), 3702(3), 3702(7), 3702(15), and 3702(20), respectively, in that pixel's modulation period. In general, a particular bit in column 3808 will be written to pixel 810 during a time interval 3702(x) in that pixel's modulation period, where x is equal to the sum of the weights of the bits previously written to pixel 810.
Column 3814 shows the row schedule for time interval 3702(0), which is determined from the update schedule in column 3812. Generally, the row schedule for each time interval 3702(0-23) is determined by the following formula:
Row=(r−mT_event)+mτ+j, (0≦j<m)
where “Row” denotes a row 814 that will be updated during the particular time interval 3702(τ), (r) represents the total number of rows 814 in display 808, T_event is the update time interval in column 3812 for a particular bit, (m) is a divisor of the number of rows 814, and (τ) is the number of the time interval 3702 that the row schedule is being calculated for. Note that because (m) rows 814 begin their modulation periods in each time interval 3702(0-23), a row update must be calculated (m) times for each bit 3808 during each time interval 3702(0-23). Accordingly, a row value is calculated for each value of (j) in the above equation for each bit in column 3808. In the present embodiment, r equals forty-eight because there are forty-eight rows 814 in display 808, the T_Event values are given in column 3812, and τ can be any number ranging from zero to twenty-three which correspond to time intervals 3702(0-23). Note that the value Row is constrained between zero and forty-seven because there are only forty-eight rows in display 808. Therefore, when subtracting or adding in the above equation, the value should not go negative or above forty-seven, but should loop forward or backward to the appropriate row value between zero and forty-seven, inclusive.
Based on this function, column 3814 shows the row schedule for time interval 3702(0) (τ=0). During time interval 3702(0), B0 bits are written to each pixel in rows 814(0) and 814(1), B1 bits are written to each pixel 810 in row 814(46) and 814(47), B2 bits are written to each pixel 810 in row 814(42) and 814(43), B3 bits are written to each pixel 810 in row 814(34) and 814(35), B4 bits are written to each pixel 810 in row 814(18) and 814(19), and B5 bits are written to each pixel 810 in row 814(8) and 814(9). Note that six even-numbered rows 814 and six odd-numbered rows 814 are updated during time interval 3702(0).
Similarly, the row schedule for time interval 3702(1) (i.e., τ=1) can also be determined and is given in column 3816. During time interval 3702(1), B0 bits are written to each pixel in rows 814(2) and 814(3), B1 bits are written to each pixel 810 in row 814(0) and 814(1), B2 bits are written to each pixel 810 in row 814(44) and 814(45), B3 bits are written to each pixel 810 in row 814(36) and 814(37), B4 bits are written to each pixel 810 in row 814(20) and 814(21), and B5 bits are written to each pixel 810 in row 814(10) and 814(11). Note again that six even-numbered rows 814 and six odd-numbered rows 814 are updated during time interval 3702(1).
It should be noted that because the number of time intervals 3702 is equal to the number of rows 814 divided by m, that the row schedule for each time interval 3702 will contain a number of row updates equal to the number of bits (b) in data word 3702 multiplied by m (i.e., b*m). In this case, where (b) equals six and (m) equals two, there are twelve rows 814 updated during each time interval 3702(0-23).
Finally, note that chart 3700 in
The driving scheme described in
To solve this problem, imager 3904(r, g, b) includes (s) iterations of pixel control circuitry, each driving one of (s) sets of rows in the display. In particular, imager 3904(r, g, b) includes a display 3908 having a plurality of rows 3914 that is controlled by two (e.g., s=2) iterations of pixel control circuitry 3916 and 3918. Pixel control circuitry 3916 drives a first set of rows 3914 and pixel control circuitry 3918 drives a second set of rows 3914. In the present embodiment, all even-numbered rows 3914(even) are assigned to a first set and all odd-numbered rows 3914(odd) are assigned to a second set. Accordingly, pixel control circuitry 3916 drives the even-numbered rows 3914(even) in display 3908 while pixel control circuitry 3918 drives all the odd-numbered rows 3914(odd). Therefore, pixel control circuitries 3916 and 3918 operate at the same speed as pixel control circuitry 3902 but together advantageously perform twice as many row updates as pixel control circuitry 3902 alone.
Like imager 2604, imager 3904(r, g, b) includes a plurality of imager inputs 3920 which include data lines and imager control lines from a display driver. The display data and control signals can be divided (e.g., according to even and odd row number) and sent to one or both of pixel control circuitries 3916 and 3918 as necessary.
Note that the modification described in
The even and odd row assignments are an easy way to assign rows 3914 in a display 3908 to one of two sets of rows. However, rows can be assigned to sets by assigning each row one of a plurality of values (e.g., 0 and 1, A, B or C, etc.) where each value identifies a particular set. The important aspect in maintaining balanced row scheduling is to update an equal number of rows 3914 assigned to each of the (s) sets during each time interval.
Although imager 3904(r, g, b) shows the case were (s) equals two, it should be noted an imager of the present invention can have any number of pixel control circuitries. Indeed, the rows 3914 in display 3908 can be assigned to three or more sets, depending on the iterations of pixel control circuitry that the imager contains. As bit depth requirements and/or the number of rows 3914 in a display 3908 increases, an imager 3904(r, g, b) could include many iterations of pixel control circuitry.
It should also be noted that the elements of an imager that are reproduced in each pixel control circuitry is flexible and may vary from system to system. For example, in one embodiment, each pixel control circuitry in imager 3904(r, g, b) could include multiple iterations of all the elements in imagers 504(r, g, b) or 2604(r, g, b) that are shown in
Furthermore, although the pixel control circuitries 3916 and 3918 are described as having particular circuit elements, their function should be thought of more generally. In particular, each pixel control circuitry 3916 and 3918 forms a pixel control unit that updates a particular set of rows 3914 in display 3908. As such, the pixel control units could be moved throughout the display system as necessary, and still provide their various functions. For example, the pixel control units could be moved from the imager to the display driver (e.g., display driver 502 or 2602). As another modification, pixel control circuitries 3916 and 3918 could be embodied as firmware or software programming in the display system 500 or 2600.
According to the modulation schemes of the present invention, the number of row updates (x) performed during one frame can be determined according to the following formula:
x=r×b,
where r equals the number of physical rows in the pixel array, and b equals the number of bits in the bit code for each data word that defines a grayscale value. For example, for imager 2604 (i.e., r=1112) and the bit code of data word 2702 (i.e., b=32), x equals 35,584 row updates (i.e., 1112*32).
As described in
Ideal_Clock=x*i*f—Vsync Hz,
where i is the number of operational instructions needed per row update and f_Vsync is the Vsync frequency. As an example, if thirty-two operational instructions are needed per row update (i.e., i=32) and there are sixty frames per second (i.e., f_Vsync=60), then the ideal clock frequency output by global timing control unit 2612 is 68,321,280 Hz. Note that the ideal clock frequency calculation given above is only an example. The ideal clock frequency calculation will vary depending on design considerations of the particular application.
In reality, it is unlikely that a clock operating at this precise frequency exists. However, a clock can be selected that generates a frequency that is slightly greater than the ideal clock frequency. For example, a real clock might generate a clock frequency at 68,335,909 Hz, which is just slightly faster than the ideal clock frequency. In this particular example, the real clock frequency is 0.02141% faster than the ideal clock frequency.
Clock generator 4104 generates a series of count pulses according to a real clock frequency and outputs the clock pulses onto clock output 4114 and, ultimately, on timing control bus 2613. Recall that clock generator 4104's frequency is faster than the ideal clock frequency. Therefore, there will be some unused time 4006 in each frame 4002 without compensation. In addition, when clock generator 4104 generates the first clock pulse in each frame 4002, it transmits a FOF signal to NOP generator 4106 via a FOF line 4120.
NOP generator 4106 is a compensator that spreads the unused time 4006 between row updates 4004(1-x) and row update 4004(x) and the next Vsync signal during each frame 4002. Because NOP generator 4106 spreads the unused time 4006 between at least some of row updates 4004, it adds portions of the unused time to at least some of the time intervals 3002, 3302. In particular, NOP generator 4106 detects row-write instructions on opcode input 4112 via input 4122, and based on the number of row-write instructions, NOP generator 4106 generates NOP opcodes and stuffs the NOP opcodes into the opcode stream entering instruction decoder 4108 via NOP line 4124. In this manner, NOP generator 4106 acts as a compensator that adjusts the duration of at least some of the time intervals 3002, 3302 depending on the unused time 4006 and the number of row updates 4004(1-x) occurring each frame 4002.
Instruction decoder 4108, responsive to clock signals received from clock generator 4104 and opcodes received via opcode input 4112 or from NOP generator 4106, decodes the opcodes and asserts the decoded operation instructions onto instruction output 41816. When instruction decoder 4108 receives a NOP opcode from NOP generator 4106, instruction decoder 4108 generates a NOP instruction and outputs the NOP instruction onto timing control bus 2613 via instruction output 4116. The elements of the display system 2600 that are connected to the timing control bus 2613, responsive to receiving a NOP instruction, are operative to ignore a clock pulse output by clock generator 4104 that corresponds with the NOP instruction.
By stuffing NOP instructions into the instruction stream (via instruction decoder 4108), NOP generator 4106 effectively slows down the output of clock generator 4104 because the elements of display system 2600 ignore particular clock pulses associated with the NOP instructions asserted on timing control bus 2613. NOP generator 4106 generates enough NOP opcodes so that the number of clock pulses effective on the display system 2600 is approximately equal to the ideal clock frequency. Effective clock pulses are pulses that are not associated with a NOP instruction.
Recall the example from
The function of NOP generator 4106 can be looked at from a different standpoint. For example, NOP generator 4106 could be viewed as increasing the ideal clock frequency to match the real clock frequency of clock generator 4104 by adding extra operational instructions to the ideal clock frequency calculation. In the particular example, the ideal clock frequency is adjusted by adding 0.00685 operational instructions to the value (i):
Ideal_Clock=x*(i+0.00685)*f—Vsync Hz.
Accordingly, substituting the same numeric values for x, i, and f_Vsync given above, the Ideal_Clock frequency becomes 68,335,905 Hz, which is approximately equal to the Real_Clock frequency of 68,335,909 Hz.
It is also important to note that NOP generator 4106, once per frame, is further operative to dynamically adjust the value of the NOP fraction that it internally accumulates responsive to each row update 4004(1-x) such that the first Vsync and the FOF signal associated with row update 4004(1) remain substantially in phase over time. In particular, NOP generator 4106 measures the phase difference between a Vsync signal received via synchronization input 4110 and the FOF signal generated by clock generator 4104. NOP generator 4106 uses the phase difference to adjust the value of the NOP fraction to increase or decrease the number of NOP opcodes that are stuffed into the instruction stream each frame 4002. The value of the NOP fraction that is accumulated during each row update 4004(1-x) is sensitive enough that NOP generator 4106 can push or pull the FOF signal substantially into phase with the first Vsync signal of each frame 4002. Because the NOP generator 4106 updates the NOP fraction each frame 4002, it synchronizes the first Vsync and the FOF signals quickly after startup.
Note that the FOF signal does not have to be generated by clock generator 4104. For example, NOP generator 4106 could alternatively watch for a particular opcode, such as a first operational instruction associated with row update 4004(1), on line 4122 to serve as a FOF signal.
It should also be noted that spreading the unused time 4006 among the row updates 4004(1-x) is particularly useful when the unused time 4006 is large enough to cause perceptible image defects. However, when the unused time 4006 is insignificant (i.e., when it doesn't degrade the displayed image), it may be more beneficial for NOP generator 4106 to stuff NOP opcodes into the instruction stream only after the last row update 4004(x) and before the next Vsync. This would put the unused time 4006 back at the end of the frame as shown in
NOP generator 4106 calculates and loads the initial value of NOP fraction 4104 at startup. In particular, after NOP generator 4106 receives a first Vsync, it waits for the last row write opcode to be asserted on opcode input 4112. Once NOP generator 4106 has determined that a last row write opcode has been asserted on opcode input 3812, it begins counting the clock pulses output by clock generator 4104 until it receives a next Vsync on synchronization input 4110. This count value represents the unused frame time 4006. Once NOP generator 4106 has determined the count value corresponding to the unused frame time 4006, it divides the count value by the number of row updates 4004(1-x) performed in a frame 3702. NOP generator 4106 then stores this quotient as the initial value of NOP fraction 4204. Note that NOP generator 4106 can determine the value of NOP fraction 4204 very quickly, but the calculation may require a few frames 4002 of time. As another option, the initial value 4204 could be pre-stored depending on the design of the display system such that NOP generator 4106 could simply load the initial value at start-up.
When NOP generator 4106 receives a next (e.g., second) Vsync signal on input 4110, NOP generator 4106 transfers and stores the new phase value 4202 as a past phase value 4206. NOP generator 4106 then determines and stores a new phase value 4202 representing the phase difference between the Vsync signal and the FOF signal associated with row update 4004(1) occurring in the new frame 4002. Then, in a subtraction operation 4208, NOP generator 4106 subtracts the new phase 4202 from the past phase 4206. NOP generator 4106 also divides the new phase value 4202 by a constant in a division operation 4210 and then, in an addition operation 4212, adds the difference from subtraction operation 4208 to the quotient calculated in the division operation 4210. In the present embodiment, the inventors have determined that dividing by four (4) in division operation 4210 yields acceptable adjustment values for the NOP fraction 3904.
Next, in another division operation 4214, NOP generator 4106 divides the sum calculated in addition operation 4212 by another constant (c) and then stores the quotient from operation 4214 as NOP fraction adjustment 4216. In the present embodiment, the value of the constant in operation 4214 depends on the number of row updates 4004(1-x) performed during each frame 4002. In particular, the constant (c) in operation 4214 is set to the following value:
c=2*log2(rb),
where r equals the number of rows 2914 in imagers 2604 and b equals the number of bits in data word 2702.
It should be noted that NOP generator 4106 can calculate a NOP fraction adjustment 42916 for the first frame 3702 it measures new phase 4202 based only on the new phase 4202. As another alternative, NOP generator 4106 could wait for two frames 4002 to calculate NOP fraction adjustment 4216 such that it had both new phase 4202 and past phase 4206.
Once NOP Fraction Adjustment 4216 is calculated, NOP generator 4106 adds the NOP fraction adjustment value 4216 to the NOP fraction 4204 in an addition operation 4218 and stores the sum as a new NOP fraction 4204. Note that NOP generator 4106 adjusts the value of the NOP fraction 4204 once per frame. In addition, NOP fraction 42904 is an unsigned binary fraction with sufficient bit-depth to permit fine adjustment of the number of NOPs output during each frame.
In contrast to NOP fraction 42904, the new phase 4202, the past phase 4206, and the NOP fraction adjustment 4216 are all signed quantities. Because these values are signed, NOP generator 4106 can adjust the value of the NOP fraction 42904 to keep Vsync and FOF in phase over many frames regardless of whether the FOF signal trails or leads the first Vsync in each frame 4002. New phase 4202, past phase 4206, and NOP fraction adjustment 4216 also have sufficient bit depth to adequately adjust the value of NOP fraction 4204
NOP generator 4106 receives a write instruction via opcode input 4112 and line 4122 for each row that is updated during a frame. For each row update 4004(1-x), an accumulator 4220 receives the updated NOP fraction 4204 and a fractional portion of an accumulated NOP value stored in accumulated NOP register 4222. The accumulator 4220 adds the two values together and stores the new accumulated NOP value in accumulated NOP register 4222. Then, NOP generator 4106 subtracts the integer portion off of the accumulated NOP value stored in accumulated NOP register 4222 and stuffs a number of NOP opcodes into the instruction stream equal to the whole portion of accumulated NOP value stored in register 42922. The fraction portion of the accumulated NOP value is saved and fed back into the accumulator 4220 during the next row update 4004. This entire process is repeated for all subsequent row updates 4004. In this manner, NOP generator 4106 spreads the unused time 4006 throughout the frame time 4002 and synchronizes the FOF signal with the first Vsync in each frame 40702. In the present embodiment, the accumulated NOP value stored in accumulated delay register 422 is an unsigned quantity.
It should be noted that, as described above, NOP generator 4106 could output NOP opcodes only after the last row update 4004(x) has occurred in each frame 4002. In such a case, accumulator 4220 would add the NOP fraction 4204 to the entire accumulated NOP value stored in register 4222 for each row update 4004(1-x). Accordingly, accumulated NOP register 4222 would output a number of NOP opcodes equal to the whole portion of the accumulated NOP value in register 4222 only after the last row update 4004(x). Any fractional portion of the accumulated NOP value in register 4222 could be truncated or added into the accumulator during the next frame 4002.
According to the operation scheme shown in
It should also be noted that although
Several modulation schemes of the present invention have now been described in detail, wherein the number of intensity values have been equal to one or two times the number of rows in the array (i.e., n=1 or n=2). However, it should be noted that the benefits of the present invention can be realized when n is assigned a value greater than two (e.g., n=3 or n=4) as long as the bit code and row balancing constraints are met. On a practical note, the value of n may often be governed by the speed limitations of the display system, because as the value of n increases, the number of time intervals (and likely row updates) will also increase.
The methods of the present invention will now be described with respect to
The description of particular embodiments of the present invention is now complete. Many of the described features may be substituted, altered or omitted without departing from the scope of the invention. For example, alternate bit codes can be used with the present invention as long as the bit-code criteria are met. As yet another example, although the embodiment disclosed is primarily illustrated as a hardware implementation, the present invention can be implemented with hardware, software, firmware, or any combination thereof. As still another example, many of the functional elements shown as part of the imagers of the present invention could be relocated to other elements of the system, such as the display driver, and still provide their respective functions. These and other deviations from the particular embodiments shown will be apparent to those skilled in the art, particularly in view of the foregoing disclosure.
This application is a division of co-pending U.S. patent application Ser. No. 11/881,732, entitled “Display Device And Driving Method,” filed Jul. 27, 2007 by the same inventors, which is incorporated by reference herein in its entirety.
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