Patent Application
20130038812
The invention relates generally to color liquid crystal display (LCD) devices and, more particularly, to LCD devices using three or more different color LEDs.
There are many known types of RGB monitors, using various display technologies, including but not limited to cathode ray tubes (CRT), light emitting displays (LED), plasma, projection displays, liquid crystal display (LCD) devices and others. Over the past few years, the use of color LCD devices has been increasing steadily. A typical color LCD device may include a light source, an array of liquid crystal (LC) elements (cells), for example, an LC array using Thin Film Transistor (TFT) active-matrix technology, as is known in the art. The device may further include electronic circuits for driving the LC array cells, e.g., by active-matrix addressing, as is known in the art, and a tri-color filter array, e.g., a RGB filter array, registered and juxtaposed on the LC array. In existing LCD devices, each full-color pixel of the displayed image is reproduced by three sub-pixels, each sub-pixel corresponding to a different color, e.g., each pixel is reproduced by driving a respective set of R, G, and B sub-pixels. For each sub-pixel there is a corresponding cell in the LC array. Back-illumination source provides the light needed to produce the color images. The transmittance of each of the sub-pixels is controlled by the voltage applied to the corresponding LC cell, based on the RGB data input for the corresponding pixel. A controller receives the input RGB data, and adjusts the magnitude of the signal delivered to the different drivers based on the input data for each pixel. The intensity of white light provided by the back-illumination source is spatially modulated by the LC array, selectively attenuating the light for each sub-pixel according to the desired intensity of the sub-pixel. The selectively attenuated light passes through the RGB color filter array, wherein each LC cell is in registry with a corresponding color sub-pixel, producing the desired color sub-pixel combinations. The human vision system spatially integrates the light filtered through the different color sub-pixels to perceive a single integrated color image.
LCDs are used in various applications. LCDs are particularly common in portable devices, for example, the small size displays of personal digital assistant (PDA) devices, game consoles, and mobile telephones, and the medium size displays of laptop (“notebook”) computers. These applications require thin and miniaturized designs and low power consumption. LCD technology is also used in non-portable devices, generally requiring larger display sizes, for example, desktop computer displays and TV sets. Different LCD applications may require different LCD designs to achieve optimal results. The more “traditional” markets for LCD devices, e.g., the markets of battery-operated devices (e.g., PDA, cellular phones, and laptop computers) require LCDs with high brightness efficiency, which leads to reduced power consumption. In desktop computer displays, high resolution, image quality and color richness are the primary considerations, and low power consumption is only a secondary consideration. Laptop computer displays require both high resolution and low power consumption; however, picture quality and color richness are compromised in many such devices. In TV display applications, picture quality and color richness are generally the most important considerations; power consumption and high resolution are secondary considerations in such devices.
A color sequential display may create a color image by dividing the color data to fields of the colors of the display and presenting these fields sequentially in time. For example, in RGB display the color data may be divided to red data, green data, and blue data, which may be displayed individually in sequence and repeated rapidly. Color sequential displays may be activated at a sufficiently high frequency to enable a viewer to temporally integrate the sequence of primary images into a full color image. Additionally, to produce a video image, the color sequential displays may be activated at a sufficiently high rate to enable reproduction of the required number of frames per second.
A sequential color LCD device may include a light source for back-illumination and an array of liquid crystal (LC) elements (cells). For example, the LC cells may be implemented using Thin Film Transistor (TFT) active-matrix technology, as is known in the art. The device further includes electronic circuits for driving the LC array cells, e.g., by active-matrix addressing, as is known in the art. The back-illumination of an RGB display may include three types of LEDs, red, green and blue, each of which color LEDs may be operated separately in a sequential manner. The transmittance of each LC cell may be controlled by the voltage applied to the LC cell and may be synchronized with the back illumination color LEDs. The color data for controlling the transmittance of each LC cell of each pixel may include, for example, the intensity of each of the colors.
U.S. Pat. No. 7,268,757 (the “'757 Patent”), the disclosure of which is incorporated herein by reference in its entirety, discloses a color LCD device for displaying a color image using at least four different colors, the device including an array of LC elements, driving circuitry adapted to receive an input corresponding to the color image and to selectively activate the LC elements of the LC array to produce an attenuation pattern corresponding to a gray-level representation of the color image, and an array of color sub-pixel filter elements juxtaposed and in registry with the array of LC elements such that each color sub-pixel filter element is in registry with one of the LC elements, wherein the array of color sub-pixel filter elements comprises at least four types of color sub-pixel filter elements, which transmit light of the at least four colors, respectively.
The '757 Patent also describes a sequential color LCD device using more than three colors. In such devices, color images may be produced by sequentially back-illuminating an array of Liquid Crystal (LC) cells with light of four or more, pre-selected, colors, producing a periodic sequence of four or more, respective, color images, which are temporally integrated into a full color image by a viewer's vision system. In some embodiments, sequential back-illumination with four or more colors is produced by sequentially filtering light through four or more, respective, color filters. In other embodiments, a multi-color light source, for example, a plurality of light emitting diodes (LEDs) capable of separately producing any of the four or more colors, activated individually by color to sequentially produce the different color back-illumination. The '757 Patent also describes a sequential LCD display of more than three colors using only red, green, and blue LEDs and operating LEDs of different colors simultaneously during the parts of the temporal sequence.
U.S. Pat. No. 5,724,062 (the “'062 Patent”) discloses a color display having a liquid crystal pixel selectably addressable during a predetermined time period, a set of at least one red, one green, and one blue color light emitting diodes positioned adjacent the liquid crystal pixel for emitting light through the liquid crystal pixel, and means connected to the liquid crystal pixel for addressing the liquid crystal pixel a plurality of times during the predetermined time period for each color so as to provide persistence when changes in color are perceived by the human eye.
According to embodiments of the invention, a liquid crystal display (LCD) device may comprise a controller operably connected to driving circuitry for a plurality of liquid crystal (LC) cells and further operably connected to an illumination control system for an array of light emitting diodes (LEDs) arranged behind said LC array and in alignment therewith, said array comprising at least three different LED colors, said controller to receive input image data, and based thereon to produce a plurality of color display frames, each said color display frame comprising color selection data for each of a plurality of display colors and color transmittance data corresponding to each said display color, sequentially send the color transmittance data for said color display frames to said driving circuitry for controlling transmittance of said LC cells, and sequentially send in synchronization with said color transmittance data said color selection data for said color display frames to said illumination control system for selectively activating said array of LEDs, wherein for at least three of the display colors, the respective color selection data represents selective illumination of LEDs of a single color, and for at least one of the display colors, said color selection data represents selective illumination of LEDs of a plurality of colors, thereby sequentially producing color display frames representing more display colors than the number of LED colors.
According to embodiments of the invention, a sequential LCD system may comprise the hereabove controller, the driving circuitry connected to said controller and operably connected to drive the plurality of liquid crystal (LC) cells, and the illumination control system connected to said controller and operably connected to selectively activate the array of light emitting diodes (LEDs). A system may further include the array of LC cells. and the array of LEDs.
According to embodiments of the invention, a method for controlling a Liquid Crystal Display (LCD) device may comprise receiving input image data; based on said input image data, producing a plurality of color display frames, each said color display frame comprising color selection data for each of a plurality of display colors and color transmittance data corresponding to each said display color; sequentially driving an array of LC cells based on color transmittance data, said sequence corresponding to said plurality of display colors; sequentially activating in synchronization with said driving of the array of LC cells said array of LEDs, wherein for at least three of the display colors, the respective color selection data represents selective illumination of LEDs of a single color, and for at least one of the display colors, said color selection data represents selective illumination of LEDs of a plurality of colors, thereby sequentially producing color display frames representing more display colors than the number of LED colors.
The invention will be understood and appreciated more fully from the following detailed description of embodiments of the invention, taken in conjunction with the accompanying drawings in which:
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.
In the following description, various aspects of the invention are described, with reference to specific embodiments that provide a thorough understanding of the invention; however, it will be apparent to one skilled in the art that the present invention is not limited to the specific embodiments and examples described herein. Further, to the extent that certain details of the devices, systems and methods described herein are related to known aspects of color display devices, systems and methods, such details may have been omitted or simplified for clarity.
Color integration by the human vision system can be performed temporally using sequential display devices, systems and methods, for example, sequential color LCD devices, using more than three colors. This concept is described in detail, in the context of sequential n-color image projection devices, in Applicants' U.S. Pat. No. 7,113,152, issued Sep. 26, 2006, entitled “Device, System and Method For Electronic True Color Display”, the entire disclosure of which is incorporated herein by reference. In sequential projection color displays devices, four or more different color fields are projected sequentially, each for a short time period, and the process is repeated periodically at a sufficiently high frequency, whereby the human vision system temporally integrates the different color fields into a full color image.
An advantage of LCD devices based on sequential color representation, in accordance with embodiments of the present invention, is that such devices can display more-than-three-color images at a resolution comparable to the resolution at which the same devices can display three-color, e.g., RGB, images. Sequential LCD display devices do not require a color sub-pixel filter matrix in registry with the LC array. Instead, each LC element controls the intensity of all the colors for a given pixel, each color being controlled during designated time slots, whereby the LC array is utilized to its full resolution. According to embodiments of the invention, color combinations may be created by sequentially back-illuminating the LC array with different colors, both individually, and in combination with other colors. In contrast to projection devices, which typically require significant physical space to contain the projection optics, namely, the optical setup that projects a miniature spatial light modulator onto a screen, the sequential LCD device of the present invention does not require projection optics and may, thus, be implemented in flat configurations.
The architecture of a flat n-color display according to an embodiment of the present invention includes an LC array (panel) having a desired size and resolution. Such LCD panels are used, for example, in portable computers as are known in the art. However, in the sequential LCD devices of the present invention, the LC panel may be used without an adjacent array of color sub-pixel filters, whereby the LC array may operate as a monochromatic gray level device with respect to each display color, and the display colors are obtained by operation of the appropriate one or more LEDs. The cells of the LC array are selectively attenuated to produce a series of more-than-three gray-level patters, each pattern corresponding to one of more-than-three color components of the displayed image. The more-than-three color components may be produced by illuminating each of the three colors red, green, and blue, as well as at least one simultaneous combination thereof. Each gray-level pattern is back-illuminated with light of the corresponding display color, where display color may refer to a single LED color or a combination of two or more LED colors illuminated simultaneously. Switching among the different back-illuminations colors is synchronized with the sequence of gray-level patterns produced by the LC array, whereby each gray level pattern in the sequence is back-illuminated with light of the selected display color, i.e., one or a combination of LED colors. The back-illumination color sequence is repeated at a sufficiently high frequency, synchronized with the periodic sequence of patters produced by the LC array, whereby the viewer perceives a full color image by temporal integration as described above.
Reference is now made to
According to embodiments of the invention, the red, green and blue LEDs may have narrow spectra. For example, the peak of the emission distribution of such devices may typically be in the range of 630-680 nm for the red emission, 500-540 nm for the green emission, and 400-480 nm for the blue emission. Other or additional color LEDs may be used. The device may further include electronic circuits for driving the LC array cells 120, e.g., by active-matrix addressing, as is known in the art. The transmittance of each of the sub-pixels may be controlled by the voltage applied to the corresponding LC cell, based on the color data input for the corresponding pixel. A controller 110 may receive the input color data, scale it to the required size and resolution of the display, and adjust the magnitude of the signal delivered to the different drivers based on the input data for each color of each pixel, e.g., the transmittance data for each LC cell to control the display intensity of each LC cell, and the color illumination data for the LED back-lighting to control which color or colors are illuminated.
The controller may include or be in communication with a formatter, which arranges the incoming input stream of RGB pixels into color field data. Each of the input data is composed of three data values, usually corresponding to red, green and blue intensities on a specific position on the display. Each color field data corresponds to all data points across all the display for the same color. The formatter may include a memory or other structure to which the data is streamed one pixel after the other and from which the data can be read according to the appropriate field order, for example, by all data relating to a selected display color. In certain cases, only parts of the fields may need to be stored. Thus, the LC transmittance data sent to the LC cell array may be synchronized with the color selection data sent to the LED back-illumination to produce a high-resolution color image by sequential display of color frames, each frame produce by illuminating each of the three LED colors individually. In the case of a display having more than three LED colors, input RGB data may be converted into the relevant more-than-three LED colors, for example, as described in U.S. Pat. No. 7,113,152, and the data for the more-than-three LED colors may then be converted into pixel data formatted to color field data, which may include at least one display color using combination of the more-than-three LED colors. The LC transmittance data sent to the LC cell array may be synchronized with the color selection data sent to the LED back-illumination to produce a high-resolution color image by sequential display of color frames, each frame produce by illuminating each of the three LED colors individually and in combinations.
The sequential LCD device in accordance with embodiments of the invention may be activated at a sufficiently high frequency to enable a viewer to temporally integrate the sequence of n-color images, e.g., n display colors using 3 LED colors, where n>3, into a full color image. Additionally, to produce a video image, the sequential LCD device in accordance with embodiments of the invention may be activated at a sufficiently high rate to enable reproduction of the required number of frames per second A sequential color LCD device that operates at a sufficiently fast rate, using back-illumination of three colors, namely, red, green, and blue light, is described in Ken-ichi Takatori, Hiroshi Imai, Rideki Asada and Masao Imai, “Field-Sequential Smectic LCD with TFT Pixel Amplifier”, Functional Devices Research Labs, NEC Corp., Kawasaki, Kagawa 216-8555, Japan, SID 01 Digest, the contents of which are incorporated herein by reference. In an embodiment of the present invention, a version of this three-color device is adapted to produce images using n display colors, where n is greater than three.
Reference is now made to
According to some exemplary embodiments of the invention, two or more LED colors may be operated simultaneously, thereby obtaining mixed colors in addition to the LED colors. For example, simultaneous operation of red and green LEDs together may create a yellow display color, simultaneous operation of red and blue LEDs together may create a magenta display color, and simultaneous operation of green and blue LEDs together may create a cyan display color. Red, green, and blue may be operated simultaneously creating a full RGB emission component, for example, white.
a is an exemplary schematic illustration of operation of red, green and blue LEDs in different combinations in order to obtain six colors, e.g., green, magenta, red, cyan, blue and yellow, according to some embodiments of the present invention. It will be recognized, as described further below, that not every combination of colors need be used in embodiments of the invention. In certain embodiments of the invention, it may be beneficial to arrange the timed order of operation of the color LEDs as depicted in
Reference is now made to
The display may load the color data row by row sequentially, for example, from the top row of the display to the bottom row of the display. For example, for LCD displays with refresh rate of 60 Hz, the frame duration may be 1/60 seconds. Since each frame consists of three sub-frames for the three colors, the sub-frame duration may be 1/180 seconds. The time delay between loading the color data of the top row to loading the color data of the bottom row may be, for example, smaller than 1/180 seconds. The back illumination reaches all rows substantially simultaneously. Therefore, there may be a phase shift between loading period of a top row 430 and loading period of a bottom row 420, the phase shift annotated by the dashed diagonal lines, as demonstrated by comparison of the loading times of the two rows depicted in
Reference is now made to
There may be a phase shift between loading period of a top row 530 and loading period of a bottom row 520, for example, because of the row-by-row loading of the data as explained above with reference to
For example, during the pulse 550 of top row 530 the ratio between red and green illumination may be substantially 1:1, and during the yellow data pulse 540 of bottom row 520 the ratio may be α:1 while α<1. Thus, the light transmitted for an open pixel during the yellow data pulse 550 at line 530 may be:
{right arrow over (P)}550=DY·({right arrow over (P)}R+{right arrow over (P)}G),
where P550 is the yellow portion 550 of a pixel having a linearized yellow data value D. PR and PG are the color of the red and the green LEDs respectively. In a similar manner, the light transmitted for an open pixel during the yellow data pulse 540 at line 520 may be:
{right arrow over (P)}
540
=D
Y·(α{right arrow over (P)}R+{right arrow over (P)}G),
where P540 is the yellow portion 440 of a pixel having a linearized yellow data value DY. Thus, the difference between the color of pixels having the same yellow value may be:
Δ{right arrow over (P)}
550−540=(1−α)·DY·{right arrow over (P)}R
The parameter a may depend on the distance of the current row from the reference row, for example the first row, thus in the general case:
Δ{right arrow over (P)}
mixed(#row)=ƒ(#row)·Dmixed·{right arrow over (P)}preceding color
Namely, for each color created by mixture of two LEDs, the difference between the color of pixels having a color data value Dmixed between current row and the reference row (Δ{right arrow over (P)}mixed) is a multiplication of a function dependent on the row number difference (ƒ(#row)), the linearized value of the color data for the relevant pixel (Dmixed), and the color of the preceding LED ({right arrow over (P)}receding color). The compensation may therefore be performed, for example, by controlling the ratio of the intensities of the preceding and the following LEDs as a function of row number (assuming that the LEDs are distributed evenly behind the rows and each LED group can be controlled independently), for example by increasing the current to the preceding LED with time so that the preceding LED intensity would increase as the row scan of the mixed field approaches the bottom of the screen, or by decreasing the current to the following LED with time so that the following LED intensity would decrease as the row scan of the mixed field approaches the bottom of the screen. Alternatively, in order to compensate for the reduced preceding color component during the mixed filed, the preceding color intensity of the same pixel may be increased by manipulating the preceding color data (Dpreceding color). Thus:
NEW Dpreceding color(#row)=Dpreceding color+ƒ(#row)·Dmixed
For the implementation of this exemplary method, the values of ƒ(#row) may be measured and kept in a lookup table. Since the phenomenon may be substantially a result of the LC cell properties, and not necessarily of the color LEDs, the same correction may apply to all mixed colors. During a scan, the values of ƒ(#row) may be retrieved from the lookup table based on the row number and multiplied by the linearized mixed data value Dmixed to obtain the linearized correction for the preceding color data value of that pixel.
Measuring ƒ(#row) may be done, for example, by activating two color LEDs together, thus creating a mixed back illumination color and driving data to the LC cells of the display and simultaneously capturing the screen using a video photometer capable of analyzing the color components and intensities of the colors in different locations of an LCD screen. Alternatively, color data can be measured in several rows, for example, three equally spaced rows, by two calibrated diodes located at each measurement point, each diode capable of measuring one color component. ƒ(#row) can than be approximated by linear, or other interpolation. Other suitable measuring techniques may apply. It will be recognized that a number of possible implementations of the method may be used, for example, a processor programmed using machine-readable instructions to perform the method.
Other multi-color displays may be obtained by changing the order of the colors or by using any sub-set of colors. For example,
In the common RGB sequential displays LC cells may typically be driven to zero transmittance prior to loading of next color data. This is dune since transition times are typically faster when a cell is driven to zero prior to loading of new data, comparing to moving from one data value to another. This may not waste a substantial amount of back illumination energy in the common RGB sequential displays since the back illumination LEDs may not be activated during the transition between colors, as explained above with reference to
In the multi-color sequential displays, for example such as in
Reference is now made to
The dependency of the target color apparent intensity in the data level of the LC cell during of the preceding color may be corrected by an algorithm for color correction. For example, an algorithm may calculate new target data level for color B based on the data level of a preceding color taking into account the increase or decrease time, so that, for example, the average apparent intensity of color B may be the required apparent intensity. For example,
According to some embodiments of the invention, new target data levels for color B based on the data level of a preceding color and the data level for color B may be measured and kept in a two-dimensional look-up table. Since the phenomena may be a result of the LCD properties and not of the color LEDs, the same correction may apply to all transition between all colors. During color data loading the values of the preceding and the current color data are used to retrieve the relevant value for the current data level from the look-up table. Alternatively, only sparse sets of values may be stored. During scan the values of the preceding and the current color data may be used to retrieve the closest values from the table and a 2D interpolation within the correction table may be applied to obtain a more accurate correction value. Alternatively, the shape of the 2D correction table can be approximated by other means.
New target data for color B based on the data of a preceding color data level and the desired data level for color B may be measured according to following procedure. First, color B apparent intensity levels for transitions from zero to color B data levels may be measured (I0=>current data). This may result in function describing the target apparent intensity of color B as a function of color B data value. Next, color B apparent intensity values for transitions from other data levels to the current color B data may be measured (Ipreceding data=>current data). Since Ipreceding data=>current data may differ from I0=>current data, the measurement is repeated with different data values until the apparent intensity of the new corrected data (Ipreceding data=>corrected current data) equals I0+>current data. This procedure may be repeated for other combination of preceding data and current data. Color apparent intensity level may be measured by photometer, spectrophotometer, a calibrated diode or any other suitable equipment capable of measuring light intensity. Other procedures for obtaining the 2D correction table may apply.
Reference is now made to
It should be noted that while in the description hereinabove, the LED colors used are red, green, and blue, LEDs of various other or additional colors corresponding to various wavelengths of light may be used for back illumination, yielding other individual and/or mixed colors. For example, more than three color LEDs, may be utilized in a similar manner.
While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
This application is a continuation application of U.S. patent application Ser. No. 12/324,136, filed Nov. 26, 2008, which claims priority from U.S. Provisional Application No. 60/996,562, filed on Nov. 26, 2007 and entitled Multiprimary Sequential LCD Panel, the entire disclosure of which is incorporated herein by reference. U.S. patent application Ser. No. 12/324,136 is a continuation-in-part application of U.S. patent application Ser. No. 12/103,269, filed Apr.15, 2008, which is a divisional application of U.S. patent application Ser. No. 11/882,491, filed Aug. 2, 2007, now U.S. Pat. No. 7,995,019, which is a continuation application of U.S. patent application Ser. No. 10/480,280, filed Dec. 11, 2003, now U.S. Pat. No. 7,268,757, which is a National Phase Application of PCT International Application No. PCT/IL02/00452, International Filing Date Jun. 11, 2002, claiming priority of U.S. Provisional Patent Application, 60/296,767, filed Jun. 11, 2001, U.S. Provisional Patent Application, 60/318,626, filed Sep. 13, 2001, and U.S. Provisional Patent Application, 60/371,419, filed Apr. 11, 2002. All of the above-mentioned applications are incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60996562 | Nov 2007 | US | |
| 60296767 | Jun 2001 | US | |
| 60318626 | Sep 2001 | US | |
| 60371419 | Apr 2002 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11882491 | Aug 2007 | US |
| Child | 12103269 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12324136 | Nov 2008 | US |
| Child | 13652329 | US | |
| Parent | 10480280 | Dec 2003 | US |
| Child | 11882491 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12103269 | Apr 2008 | US |
| Child | 12324136 | US |
