Patent Application
20140071183
This application claims priority to Japanese Patent Application No. 2012-199616 filed on Sep. 11, 2012. The entire disclosure of Japanese Patent Application No. 2012-199616 is hereby incorporated herein by reference.
1. Technical Field
The present invention relates to a method for driving an electrophoretic display device, an electrophoretic display device, an electronic apparatus, an electronic timepiece, and the like.
2. Background Technology
In recent years, display panels having a memory property whereby an image can be displayed even when the power is turned off have been developed, and have been put to use in electronic apparatuses such as electronic timepieces. Electrophoretic display devices (EDD), memory liquid crystal display devices, and the like are known display panels having a memory property.
Electrophoretic display devices have the advantage of being excellent in terms of wide viewing angle, high contrast ratio, flexibility, low power consumption, and so forth. An electrophoretic display device displays an image by using an applied electric field to move, for example, white and black charged electrophoretic particles. The charged particles move through a dispersion solution; however, for example, the viscosity of the dispersion solution is temperature-dependent. For this reason, a change in temperature can sometimes result in a display image appearing differently, even when an identical electric field is applied.
In view whereof, for example, the invention of Patent Document 1 changes the durations of a reset pulse and a drive pulse on the basis of the temperature. So doing compensates for the effects of temperature changes and achieves an improvement in the image quality.
Japanese Laid-open Patent Publication No. 2007-505351 (national-phase translation of international application, Patent Document 1) and Japanese Laid-open Patent Publication No. 2005-530201 (national-phase translation of international application, Patent Document 2) are examples of the related art.
However, as is described in Patent Document 2, a concern also arises in that in an electrophoretic display device, when the time average of the electric field applied between the electrodes is not substantially zero, the operating life of the device will be shorter. In other words, ensuring the long-term reliability of an electrophoretic display device necessitates striking a DC balance, i.e., having the time average of the electric field being applied be substantially zero.
However, in the invention in Patent Document 1, the duration of the drive pulse and the duration of the reset pulse are established on the basis of scaling functions which are each independent. Accordingly, a deviation arises in the direction and magnitude of the electric field being applied between the electrodes, and thus in the invention in Patent Document 1, it is difficult to ensure the long-term reliability of the electrophoretic display device.
A separate problem suffered in the invention in Patent Document 1 is that even were the durations of the reset pulse and the drive pulse to be identical, the refresh time for an image would be increased. An electrophoretic display device is able to display an image in either a full-screen drive format, in which the entirety of a display unit is rendered, or a partial drive format, which also allows for rendering of a part that is intended to be written over. The invention in Patent Document 1 is premised on the full-screen drive format, and the refresh time for an image is so remarkably delayed as to not be practical when the durations for the reset pulse and the drive pulse are aligned, i.e., matched to the longer of the durations.
The invention has been contrived in view of the problems of such description. According to several aspects of the invention, provided is, inter alia, a method for driving an electrophoretic display device making it possible to use a partial drive format, which allows for a shorter refresh time for an image, to also compensate for the effects of temperature changes while still striking a DC balance.
A first aspect of the invention is a method for driving an electrophoretic display device. The display includes a display unit in which electrophoretic elements including electrophoretic particles are sandwiched between a pair of substrates and which includes pixels capable of displaying at least a first color and a second color, pixel electrodes corresponding to the pixels disposed between the substrates and the electrophoretic elements, a common electrode that faces the plurality of pixel electrodes disposed between the other of the substrates and the electrophoretic elements, and a temperature detection unit configured to measure a temperature of the display unit.
The method includes:
causing the display unit to display a first image in the first color by a partial drive format, in which a voltage based on a drive pulse signal repeating a first electric potential and a second electric potential is applied to the common electrode and a voltage based on a normal signal or an inverse signal of the drive pulse signal is applied to each of the plurality of pixel electrodes, thus causing the electrophoretic particles to be moved by an electric field produced between the pixel electrodes and the common electrode;
causing the display unit to display a background of the first image in the first color by the partial drive format, after the causing the display unit to display the first image in the first color;
causing the display unit to display a background of a second image in the second color, by the partial drive format; and
causing the display unit to display the second image in the second color by the partial drive format, after the causing the display unit to display the background of the second image; and wherein
in a case where the temperature detection unit detects a predetermined change in temperature after the causing the display unit to display the background of the second image and before the casing the display unit to display the second image in the second color,
causing the display unit to display a predetermined image by using the drive pulse signal adjusted on the basis of a temperature after the change, and
causing the display unit to complementarily display the predetermined image by using the drive pulse signal adjusted on the basis of the temperature after the change, are executed after the causing the display unit to display the second image in the second color, and
a subsequent iteration of the causing the display unit to display the first image in the first color is executed after the causing the display unit to complementarily display the predetermined image.
According to the invention, at least four steps are executed by the partial drive format. The four steps are the first image display step for causing the first image to be displayed in the first color, the first image erasing step for causing the background of the first image to be displayed in the first color, the second image display step for causing the background of the second image to be displayed in the second color, and the second image erasing step for causing the second image to be displayed in the second color.
The electrophoretic display device for carrying out the method of driving of the invention includes the temperature detection unit for detecting a change in temperature of the display unit. The temperature detection unit includes, for example, a temperature sensor for detecting the temperature of the display unit. The temperature sensor can measure the temperature directly, by contact with the display unit, or can be arranged in the vicinity of the display unit and establish the temperature by, for example, a calculation. The temperature detection unit detects whether or not there is a predetermined change in temperature (for example, a change of 3° or more) on the basis of the temperature of the display unit received from the temperature sensor.
According to the invention, the first afterimage erasing step and the second afterimage erasing step are executed in a case where the temperature detection unit detects the predetermined change in temperature after the second image display step and before the second image erasing step. In other words, two steps in which the drive pulse signal that has been adjusted on the basis of the temperature after the change are added after the four steps in which the drive pulse signal that has been adjusted on the basis of the temperature before the change is used. These two added steps makes it possible to remove the afterimage that can be produced by a change in temperature of the display unit and to compensate for the effects of the change in temperature. At this time, there is no need for the two additional steps to be executed immediately in a case where the temperature detection unit detects the predetermined change in temperature. For example, in an example of a time display described below (see
In the partial drive format, a voltage based on a drive pulse signal repeating a first electric potential and a second electric potential is applied to the common electrode and a voltage based on a normal signal or an inverse signal of the drive pulse signal is applied to each of the plurality of pixel electrodes, thus causing the electrophoretic particles to be moved by an electric field produced between the pixel electrodes and the common electrode and thereby writing over an image being displayed on the display unit. The partial drive format makes it possible to render not only the entirety of the display unit but also solely a part that is intended to be written over.
According to the invention, the first image display step, the first image erasing step, the second image display step, and the second image erasing step include rendering a part of the display unit by the partial drive format, and therefore a shorter refreshing time for the images is possible in comparison to a full-screen drive format in which the entirety of the display unit is rendered at all times. Preferably, the additionally executed first afterimage erasing step and second afterimage erasing step use the partial drive format, in order to shorten the refreshing time for the images, but it would also be possible to use the full-screen drive format.
In the method for driving an electrophoretic display device of the invention, in a case where the predetermined change in temperature is not detected, the entirety of the display unit is displayed in the first color in the first image display step and the first image erasing step in conjunction. Then, the entirety of the display unit is displayed in the second color in the second image display step and the second image erasing step in conjunction. For this reason, a DC balance can be struck among the four steps.
In a case where the predetermined change in temperature is detected, a DC balance can be struck between the first afterimage erasing step for causing the predetermined image to be displayed and the second afterimage erasing step for causing the predetermined image to be complementarily displayed. For example, the predetermined image is understood to be a single-color display in which the entirety of the display unit is the first color. At this time, the entirety of the display unit is the first color in the first afterimage erasing step, and is complementarily displayed in the second afterimage erasing step. “Complementary display” signifies in principle that a portion that was not displayed in the first color in the first afterimage erasing step would be displayed in the second color, but in a case where a single-color display of the first color is used, it would be exceptionally possible for the entirety of the display unit to be displayed in the second color. In other words, the entirety of the display unit is displayed inverted in the second afterimage erasing step, and therefore a DC balance can be struck between the two steps.
When the first afterimage erasing step and the second afterimage erasing step use the full-screen drive format, the predetermined image will be displayed inverted in the second afterimage erasing step, irrespective of what kind of image the predetermined image is, and thus a DC balance can be struck between these two steps.
Accordingly, the method for driving an electrophoretic display device of the invention makes it possible to also compensate for the effects of a change in temperature while still striking a DC balance. For this reason, the long-term reliability can be ensured, and the display quality is enhanced. Also, because the partial drive format is still used, it is possible to shorten the refresh time for an image in comparison to a case where solely the full-screen drive format is used.
The “first color” is, for example, black, and the “second color” is, for example, white. The first image and the second image are an image displayed on a part of the display unit, and can be either letters, numbers, text, figures, symbols, patterns, or the like, or a combination thereof. The first image and the second image can also change to different letters, numbers, text, figures, symbols, patterns, or the like every time a display is effected in the first image display step and the second image display step. The background of the first image and the background of the second image refer to portions other than the first image and portions other than the second image, respectively, on the display unit.
A second aspect of the invention is a method for driving an electrophoretic display device including a display unit in which electrophoretic elements including electrophoretic particles are sandwiched between a pair of substrates and which includes pixels capable of displaying at least a first color and a second color, pixel electrodes corresponding to the pixels disposed between one of the substrates and the electrophoretic elements and a common electrode that faces the plurality of pixel electrodes disposed between the other of the substrates and the electrophoretic elements, and a temperature detection unit configured to measure a temperature of the display unit, wherein the method includes:
causing the display unit to display a first image in the first color by a partial drive format, in which a voltage based on a drive pulse signal repeating a first electric potential and a second electric potential is applied to the common electrode and a voltage based on a normal signal or an inverse signal of the drive pulse signal is applied to each of the plurality of pixel electrodes, thus causing the electrophoretic particles to be moved by an electric field produced between the pixel electrodes and the common electrode; and
causing the display unit to display a background of the first image in the first color by the partial drive format, after the causing the display unit to display the first image in the first color; and wherein
in a case where the temperature detection unit detects the predetermined change in temperature after the causing the display unit to display the first image in the first color and before the causing the display unit to display the background of the first image in the first color,
causing all the pixels of the display unit to be displayed in the second color by using the drive pulse signal adjusted on the basis of the temperature before the change,
causing the display unit to display a predetermined image by using the drive pulse signal adjusted on the basis of the temperature after the change, and
causing the display unit to complementarily display the predetermined image by using the drive pulse signal adjusted on the basis of the temperature after the change, are executed after the causing the display unit to display the background of the first image in the first colort, and
a subsequent iteration of the causing the display unit to display the first image in the first color is executed after the causing the display unit to complementarily display the predetermined image.
According to the invention, the first image display step for causing the first image to be displayed in the first color and the first image erasing step for causing the background of the first image to be displayed in the first color are executed by the partial drive format. The electrophoretic display device for carrying out the method of driving of the invention includes the temperature detection unit for detecting a change in temperature of the display unit, and detects whether or not there has been a predetermined change in temperature.
According to the invention, the first single-color display step, the first image erasing step, and the second image erasing step are executed in a case where the temperature detection unit detects the predetermined change in temperature after the first image display step and before the first image erasing step. In other words, the first single-color display step in which the drive pulse signal that has been adjusted on the basis of the temperature before the change is used and the two steps in which the drive pulse signal that has been adjusted on the basis of the temperature after the change is used (the first afterimage erasing step and the second afterimage erasing step) are added after the two steps in which the drive pulse signal that has been adjusted on the basis of the temperature before the change is used (the first image display step and the first image erasing step). These three added steps make it possible to remove the afterimage that can be produced by a change in temperature of the display unit and to compensate for the effects of the change in temperature, while still striking a DC balance. At this time, there is no need for the three additional steps to be executed immediately in a case where the temperature detection unit detects the predetermined change in temperature. For example, in an example of a time display described below (see
According to the invention, the first image display step and the first image erasing step include rendering a part of the display unit by the partial drive format, and therefore a shorter refreshing time for the images is possible in comparison to a full-screen drive format in which the entirety of the display unit is rendered at all times. Herein, the first single-color display step requires that the entirety of display unit be set to the second color by the partial drive format in order to strike a DC balance. Preferably, the first afterimage erasing step and the second afterimage erasing step use the partial drive format, in order to shorten the refreshing time for the images, but it would also be possible to use the full-screen drive format.
In the method for driving an electrophoretic display device of the invention, the entirety of the display unit is displayed in the first color in the first image display step and the first image erasing step in conjunction. Then, in a case where the predetermined change in temperature is detected, the added first single-color display step includes displaying the entirety of the display unit in the second color, and therefore a DC balance can be struck among these three steps. As stated earlier, a DC balance can also be struck between the first afterimage erasing step and the second afterimage erasing step.
In a case where the predetermined change in temperature is not detected, then a step for causing the entirety of the display unit to be displayed in the second color should be executed instead of the first single-color display step. For example, the entirety of the display unit could be displayed in the second color in the second image display step and the second image erasing step in conjunction.
Accordingly, the method for driving an electrophoretic display device of the invention makes it possible to also compensate for the effects of a change in temperature while still striking a DC balance. For this reason, the long-term reliability can be ensured, and the display quality is enhanced. Also, because the partial drive format is still used, it is possible to shorten the refresh time for an image in comparison to a case where solely the full-screen drive format is used.
A third aspect can be the method for driving an electrophoretic display device, wherein in a case where the temperature detection unit detects the predetermined change in temperature after the causing the display unit to display the first image in the first color and before the causing the display unit to display the background of the first image,
causing all the pixels of the display unit to be displayed in the second color by using the drive pulse signal, which has been adjusted on the basis of the temperature before the change, and
the causing the display unit to display the predetermined image and the causing the display unit to complementarily display the predetermined image are executed after the first image erasing step.
According to the invention, the first single-color display step, the first image erasing step, and the second image erasing step are executed in a case where the temperature detection unit detects the predetermined change in temperature after the first image display step and before the first image erasing step. In other words, the first single-color display step in which the drive pulse signal that has been adjusted on the basis of the temperature before the change is used and the two steps in which the drive pulse signal that has been adjusted on the basis of the temperature after the change is used are added after the two steps in which the drive pulse signal that has been adjusted on the basis of the temperature before the change is used. These three added steps make it possible to remove the afterimage that can be produced by a change in temperature of the display unit and to compensate for the effects of the change in temperature, while still striking a DC balance.
Accordingly, the method for driving an electrophoretic display device of the invention makes it possible to compensate for the effects of a change in temperature while still striking a DC balance not only in a case where the temperature detection unit detects the predetermined change in temperature after the second image display step and before the second image erasing step, but also in a case where the temperature detection unit detects the predetermined change in temperature after the first image display step and before the first image erasing step.
A fourth aspect can be the method for driving an electrophoretic display device, wherein the causing the display unit to display the predetermined image and the causing the display unit to complementarily display the predetermined image use a single-color display as the predetermined display.
According to the invention, a single-color display is used as the predetermined display of the first afterimage erasing step and the second afterimage erasing step. A “single-color display” is, for example, a display in which the entirety of the display unit is set to the first color. At this time, because the entirety of the display unit will be set to the second color by the second afterimage erasing step, it is possible to execute the first image display step in succession. That is to say, the method for driving an electrophoretic display device of the invention obviates the need for a second single-color display step (described below), and makes it possible to compensate for the effects of a change in temperature while still striking a DC balance in fewer steps.
A fifth aspect can be the method for driving an electrophoretic display device, wherein the causing the display unit to display the predetermined image and the causing the display unit to complementarily display the predetermined image use a single-color display as the predetermined display, and
causing all the pixels of the display unit to be displayed in the second color by using the drive pulse signal, which has been adjusted on the basis of the temperature after the change, is executed after the causing the display unit to complementarily display the predetermined image.
A sixth aspect can be the method for driving an electrophoretic display device, wherein the causing the display unit to display the predetermined image and the causing the display unit to complementarily display the predetermined image use a checkered pattern as the predetermined display.
According to these aspects, it is possible to use a display other than a single-color display, such as, for example, a checkered pattern, as the predetermined display of the first afterimage erasing step and the second afterimage erasing step. For this reason, it is possible to use any desired image that is highly effective in removing the afterimage that can be produced by a change in temperature of the display unit.
At this time, in some instances the partial drive format might be used in the first afterimage erasing step and the second afterimage erasing step in order to accelerate the refreshing time for the display images. In such a case, a DC balance can be struck when the second single-color display step for causing the entirety of the display unit to be displayed in the second color by using the drive pulse signal that has been adjusted on the basis of the temperature after the change is added after the second afterimage erasing step.
The method for driving an electrophoretic display device of these aspects makes it possible to remove the afterimage that can be produced by a change in temperature by using a display other than a single-color display, such as, for example, a checkered pattern, and therefore allows for further enhancement of the display quality.
A seventh aspect of the invention can be an electrophoretic display device provided with a control unit for executing the method for driving an electrophoretic display device.
According to the invention, the method of driving is realized by a control unit included in an electrophoretic display device. For this reason, the electrophoretic display device of the invention makes it possible to erase the afterimage that can be produced in a case where a change in temperature has occurred, while still striking a DC balance. For this reason, the long-term reliability is excellent and an afterimage is prevented from appearing, thereby offering a better appearance and improved display quality.
An eighth aspect of the invention can be an electronic apparatus including the electrophoretic display device.
A ninth aspect of the invention can be an electronic timepiece including the electrophoretic display device.
By using the electrophoretic display device, the electronic apparatus and electronic timepiece of these aspects of the invention make it possible to erase the afterimage that can be produced in a case where a change in temperature has occurred, while still striking a DC balance. For this reason, an electronic apparatus or electronic timepiece of excellent long-term reliability and favorable display quality can be realized.
Referring now to the attached drawings which form a part of this original disclosure:
The first embodiment of the invention shall now be described with reference to
An electrophoretic display device 10 includes a display control circuit 60, a temperature sensor 65, and a display unit 3. The display control circuit 60 is a control unit for controlling the display unit 3, and includes a scan line drive circuit 61, a data line drive circuit 62, a controller 63, a shared power source modulation circuit 64, and a storage unit 160.
The scan line drive circuit 61, the data line drive circuit 62, the shared power source modulation circuit 64, and the storage unit 160 are each connected to the controller 63. The controller 63 has comprehensive control thereof, based on an input signal (not shown) such as, for example, a time signal.
The storage unit 160 can include, for example, a video random access memory (VRAM) as well as nonvolatile memory such as, for, example, a flash memory (not shown). The VRAM stores data regarding an image to be displayed on the display unit 3. The VRAM can be divided into a plurality of banks, each of which would then function as an individual VRAM. The nonvolatile memory stores data regarding elements constituting the data stored in the VRAM (for example, parts data and background data). The storage unit 160 additionally includes, for example, a static random access memory (SRAM) or a dynamic random access memory (DRAM), and is used by the controller 63 as a temporary storage region for data.
The temperature sensor 65 measures the temperature of the display unit 3 and outputs temperature data to the controller 63. The controller 63 compares the received temperature data and temperature data of the past, which is stored in the storage unit 160, to detect whether or not there has been a predetermined change in temperature (for example, a change of 3° or more). The temperature sensor 65, the controller 63, and the storage unit 160 constitute a temperature detection unit of the invention. The controller 63 controls the shared power source modulation circuit 64 and adjusts the drive pulse signal in a case where there has been the predetermined change in temperature.
A plurality of scan lines 66 which extend from the scan line drive circuit 61 and a plurality of data lines 68 which extend from the data line drive circuit 62 are formed on the display unit 3, and a plurality of pixels 40 are provided in correspondence to positions of intersection thereof.
The scan line drive circuit 61 is connected to each of the pixels 40 by m scan lines 66 (Y1, Y2, . . . , Ym). By sequentially selecting a scan line 66, from the first row to the m-th row, in conformity with the control of the controller 63, the scan line drive circuit 61 supplies a selection signal for defining the ON timing for a driving thin-film transistor (TFT) 48 (see
The data line drive circuit 62 is connected to each of the pixels 40 by n data lines 68 (X1, X2, . . . , Xn). The data line drive circuit 62 supplies to the pixels 40 an image signal for defining image data regarding the one bit corresponding to each of the pixels 40, in conformity with the control of the controller 63. The present embodiment is understood to be such that a low-level image signal is supplied to the pixels 40 in a case where pixel data “0” is defined, and a high-level image signal is supplied to the pixels 40 in a case where pixel data “1” is defined.
Also provided to the display unit 3 are a low potential power source line 49 (Vss), a high potential power source line 50 (Vdd), a common electrode wiring 55 (Vcom), a first pulse signal line 91 (S1), and a second pulse signal line 92 (S2), all of which extend from the shared power source modulation circuit 64; each of the wirings is connected to the pixels 40. In conformity with the control of the controller 63, the shared power source modulation circuit 64 generates a variety of signals to be supplied to each of the wirings, and in turn either electrically connects or disconnects (causes a high impedance, or “Hi-Z”, in) each of the wiring.
The driving TFT 48, a latch circuit 70, and a switch circuit 80 are provided to the pixels 40. The pixels 40 have a configuration of an SRAM format, in which an image signal is retained as an electric potential by the latch circuit 70.
The driving TFT 48 is a pixel switching element including an N-type metal-oxide-semiconductor (N-MOS) transistor. A gate terminal of the driving TFT 48 is connected to the scan line 66, a source terminal is connected to the data line 68, and a drain terminal is connected to a data input terminal of the latch circuit 70. The latch circuit 70 is provided with a transfer inverter 70t and a feedback inverter 70f. A power source voltage is supplied from the low potential power source line 49 (Vss) and the high potential power source line 50 (Vdd) to the transfer inverter 70t and the feedback inverter 70f.
The switch circuit 80 includes transmission gates TG1 and TG2, and outputs a signal to a pixel electrode 35 (see
When pixel data “1” (a high-level image signal) is stored in the latch circuit 70 and the transmission gate TG1 is in an ON state, then the switch circuit 80 supplies the signal S1 as the Va. However, when pixel data “0” (a low-level image signal) is stored in the latch circuit 70 and the transmission gate TG2 is in an ON state, then the switch circuit 80 supplies the signal S2 as the Va. The circuitry configuration of such description makes it possible for the display control circuit 60 to control the electric potential (signal) supplied to the pixel electrodes of each of the pixels 40.
The electrophoretic display device 10 of the present embodiment is understood to be an electrophoretic format of a two-particle microcapsule type. Assuming the dispersion solution to be colorless and translucent, and assuming the electrophoretic particles to be either white or black, at least two different colors can be displayed, with the two colors of white and black serving as basic colors. Herein, the electrophoretic display device 10 is described as being able to display black and white as basic colors. Thus, “inversion” is an expression indicating that pixels that were being displayed in black are displayed in white, or that pixels that were being displayed in white are displayed in black.
The counter substrate 131, meanwhile, is a translucent substrate; images are displayed on the counter substrate (131)-side on the display unit 3. The display unit 3 includes a common electrode layer 370 in which a flat-shaped common electrode 37 is formed on the electrophoretic element (132)-side of the counter substrate 131. The common electrode 37 is a translucent electrode. The common electrode 37, unlike the pixel electrodes 35, is an electrode shared by all the pixels, to which an electric potential Vcom is supplied.
The electrophoretic element 132 is arranged in an electrophoretic display layer 360 provided between the common electrode layer 370 and the drive electrode layer 350, the electrophoretic display layer 360 serving as a display region. Each of the pixels can be made to display a desired display color, depending on the electric potential difference between the common electrode 37 and the pixel electrode (for example, 35A or 35B).
In
In
First, the drive formats for the pulse signals when a control unit (to which the display control unit 60 in
The Vcom in
In this example, the pulse signal giving the electric potential Va to be applied to the pixel electrode of the pixel 40A is an inverse signal of the drive pulse signal. Also, the pulse signal giving the electric potential Vb to be applied to the pixel electrode of the pixel 40B is the same signal as the drive pulse signal (a normal signal). The pixel 40A and the pixel 40B are, for example, the two pixels illustrated in
The pixel 40B, however, continues displaying black from the beginning, without experiencing any electric potential difference, because the same signal as with Vcom is supplied at all times to the pixel electrode. Thus, in the partial drive format, it is possible to drive solely those pixels which should be changed, and possible to increase the response speed in rewriting the pixels. In particular, the use of the inverse potential drive pulse having a shorter pulse width makes it possible to curtail the drive time in partial rewriting.
Being suitable for cases where a part that is intended to be rewritten is rendered, the format for driving a pulse signal of such description is accordingly termed a partial drive format. However, the partial drive format in no way limits the intention of rewriting to solely some of the pixels of the display unit. For this reason, it is possible to render all of the pixels of the display unit in the partial drive format.
In
However, when the display refreshing of such description is continued for a long time, in some instances a local drop in the contrast ratio is produced.
Herein, the local drop in the contrast ratio is produced by the long-term repeated application of an electric field to the region 51, which is a part of the display unit 3. In other words, the number of times the signal used to apply the voltage is driven for the region 51 and the number of times the signal is driven for regions other than the region 51 (for example, the region 52) begins to vary considerably over time. A local drop in the contrast ratio such as in
The pixel 40B, in turn, is displayed in white at first. An interval corresponding to T3 in
Herein, in the full-screen drive format, an electric potential of either VL or VH is applied to the pixel electrodes of all the pixels of the display unit 3. Because there is no long-term repeated application of an electric field to solely a region that is a part of the display unit, no local drop in the contrast ratio will be produced.
In the full-screen drive format, all of the pixels of the display unit are subject to being rendered, and it is not possible to rewrite only some of the pixels of the display unit. In keeping with the name therefor, all of the pixels of the display unit will be rendered.
The display image is then refreshed, where the refreshed image is understood to be an image in which the upper half, which includes the region X and the region Y, is black. At this time, in order to strike a DC balance, the display is first inversed, as in
Thereafter, as in
Herein, in a case where there is a sufficiently long time for driving the pulse signals in the full-screen drive format (a case where TD is extended by an amount commensurate with TEX), then both the pixel 40A and the pixel 40B converge on the reflectivity RC (=R1) of
Accordingly, though no local drop in the contrast ratio is produced, a case where the full-screen drive format is carried out rather than the partial drive format still has another problem in the concern that an afterimage will be generated. For this reason, there has been a need for a method for driving an electrophoretic display device whereby neither the problem of a local drop in the contrast ratio nor the problem of an afterimage will be generated.
A display example in the present embodiment shall now be described, with reference to
1.5.1. Case where there is No Change in Temperature
The names of the steps in
Herein, a control unit of the electrophoretic display device of the present embodiment carries out a control in which the image of the display unit is refreshed from an original image that has already been displayed to a subsequent new image. In other words, a control for erasing the original image and display the new image is executed.
The control for erasing the original image and the control for displaying the new image are executed in a predetermined sequence. Each of the stages for executing the control relating to the refreshing of the image is termed a “step”. For example, a stage at which the control unit executes a first image display control is expressed as a first image display step. The execution of a corresponding control by the control unit in each of the steps is expressed hereinbelow simply as “a [ . . . ] step is executed” or “[ . . . ] executes a [ . . . ] step”. For example, the execution of the first image display control by the control unit in the first image display step is expressed simply as “the first image display step is executed” or “[ . . . ] executes the first image display step”.
Hereinafter,
These steps (the first image display step, the first image erasing step, the second image display step, and the second image erasing step) are all in the partial drive format, and the afterimage that is produced when the time for processing to refresh the display image is curtailed in the full-screen drive format will not be generated.
Herein, when the drive pixels 13 of the first image display step (1) in
There is no change in temperature during the execution of these four steps. Herein, that there is no change in temperature signifies that there is no change in temperature not less than a predetermined temperature. The “predetermined temperature” can be established in a fixed manner, such as, for example, 3°, or can be established on the basis of a table in which temperatures and drive pulse signals are associated together, such as in the present embodiment.
At this time, for example, where the temperature of the display unit 3 is TP1, then a drive pulse signal that has been adjusted for the temperature TP1 (hereinafter referred to as simply “TP1”) is used in all four steps, as in
The description relates now to
The notations enclosed by parentheses affixed after the corresponding steps in
To summarize the description above, in a case where there is no change in temperature, the method for driving an electrophoretic display device in the present embodiment does not produce the problem of a local drop in the contrast ratio, which can be produced in the partial drive format. In other words, all of the pixels of the entirety of the display unit are changed either to black (the first image display step and the first image erasing step), or to white (the second image display step and the second image erasing step), and thus the electric field is applied uniformly to the entirety of the display unit.
The local drop in the contrast ratio is produced by the long-term repeated application of an electric field to a region that is solely a part (hereinafter, a “specific region”) of the display unit. In other words, the number of times the signal used to apply the voltage is driven for the specific region and the number of times the signal is driven for regions other than the specific region begins to vary considerably over time. In the method for driving an electrophoretic display device in the invention, no such specific region will be produced, and thus no local drop in the contrast ratio will be generated.
Accordingly, in a case where there is understood not to be a change in temperature, the method for driving an electrophoretic display device in the present embodiment produces neither a local drop in the contrast ratio nor an afterimage, while still striking a DC balance, and thus the long-term reliability can be ensured and the display quality is enhanced.
In a case where there is a change in temperature, when a drive pulse signal that has been adjusted on the basis of the temperature before the change is used to either display or erase an image, then the charged particles are subjected to either too much or too little energy for moving same through the dispersion solution (herein, the total reached by multiplying the applied electric field by the application time is referred to as the energy), and thus in some instances the display will not be the desired display of either black or white, and an afterimage will be produced.
By way of example, the temperature is understood to have changed from TP1 to TP2 during the about one minute of time display (in this example, “10:06”) after the second image display step of
The description again referring to
At this time, in the first afterimage erasing step and the second afterimage erasing step, the afterimage can be erased because the drive pulse signal that has been adjusted to TP2, which is the temperature after the change, is used. Also, the use of the single-color display of black (corresponding to the first color) as the predetermined image causes the complementary display of the second afterimage erasing step to be an inverse display of the predetermined image, and strikes a DC balance between the two steps.
As per the foregoing, the method for driving an electrophoretic display device of the present embodiment makes it possible, even in a case where there is a change in temperature after the second image display step and before the second image erasing step, to also compensate for the effects of a change in temperature (more specifically, an afterimage such as that in
By way of example, the temperature is understood to have changed from TP3 to TP4 during the about one minute of time display (in this example, “10:05”) after the first image display step of
The description again referring to
At this time, the afterimage can be erased, because in the first afterimage erasing step and the second afterimage erasing step, the drive pulse signal that has been adjusted to TP4, which is the temperature at the change, is used. Also, the use of the single-color display of black (corresponding to the first color) as the predetermined image causes the complementary display of the second afterimage erasing step to be an inverse display of the predetermined image, and strikes a DC balance between the two steps.
However, unlike the case where there is a change in temperature after the second image display step and before the second image erasing step, the steps in which the drive pulse signal that has been adjusted to TP3, which is the temperature before the change, are solely the first image display step of
After the execution of the second image erasing step in
As per the foregoing, the method for driving an electrophoretic display device of the present embodiment makes it possible, even in a case where there is a change in temperature after the first image display step and before the first image erasing step, to also compensate for the effects of a change in temperature (more specifically, an afterimage such as that in
The display examples of the present embodiment were represented by dividing cases between whether or not there was a change in temperature; the flow chart in
First, the register is set to “0” to initialize the register (S1). The first image display step (S2), in which the first image (for example, in the example in
Herein, the register is set to “1” (S8) in a case where the temperature detection unit does not detect the predetermined change in temperature (for example, a change in temperature of such an extent that a difference of two stages is produced in the table in
In a case where the temperature detection unit does detect the predetermined change in temperature after the first image display step and before the first image erasing step (S6: Yes), however, then the first single-color display step is executed (S10) and all of the pixels of the display unit 3 are displayed in the second color (white). In the first single-color display step, a drive pulse signal that has been adjusted on the basis of the temperature before the change is used.
Thereafter, the first afterimage erasing step (S12) and the second afterimage erasing step (S14) are executed using a drive pulse signal that has been adjusted on the basis of the temperature after the change, whereby the afterimage caused by the change in temperature is erased. At this time, for example, the entirety of the display unit can be displayed in black in the first afterimage erasing step, the entirety of the display unit then also being displayed in white in the second afterimage erasing step (see
In the present embodiment, the partial drive format is used in the first afterimage erasing step (S12) and the second afterimage erasing step (S14) as well. However, the full-screen drive format can also be used for the first afterimage erasing step and the second afterimage erasing step. In such a case, for any desired image, a normal display and an inverse display would be executed in the first afterimage erasing step and the second afterimage erasing step. For this reason, an image other than a single-color display can be used without the need to increase the number of steps.
After the steps S18 and S18, a determination is made as to whether or not the value of the register is “0” (S20). When the value of the register is “0”, then there is no need to execute the second image display step and the second image erasing step, and thus the flow returns to the first image display step (S2) (S20: Yes). When the value of the register is “1” (S20: No), however, then there has been no change in temperature after the first image display step and before the first image erasing step, and therefore the second image display step (S22) and the second image erasing step (S24) are executed.
The second image display step causes the background of the second image (for example, in the example in
In a case herein where the temperature detection unit does not detect the predetermined change in temperature after the second image display step and before the second image erasing step (S26: No), then the register is set to “0” (S18) and the determination of the value of the register (S20) is executed.
In a case where the temperature detection unit does detect the predetermined change in temperature after the second image display step and before the second image erasing step (S26: Yes), however, then the afterimage caused by the change in temperature is erased by the execution of the first afterimage erasing step (S12) and the second afterimage erasing step (S14) using a drive pulse signal that has been adjusted on the basis of the temperature after the change. After the second afterimage erasing step (S14) has been executed, the register is set to “0” (S18) and the determination of the value of the register (S20) is executed.
In this manner, in the method for driving an electrophoretic display device in the present embodiment, a DC balance is struck irrespective of whether or not there has been a change in temperature, and in a case where a change in temperature has taken place, then the afterimage caused by the change in temperature is erased by the execution of the first afterimage erasing step and the second afterimage erasing step in which the drive pulse signal that has been adjusted on the basis of the temperature after the change is used. For this reason, the long-term reliability can be ensured, and the display quality is enhanced. Also, because the partial drive format is still used, it is possible to shorten the refresh time for an image in comparison to a case where solely the full-screen drive format is used.
The second embodiment of the invention shall now be described, with reference to
The configuration of the electrophoretic display device of the second embodiment is the same as that of the first embodiment as well, and thus a description thereof has been omitted. The circuitry configuration of the pixel portion, the display format, and the like are also the same as those of the first embodiment. In the method for driving an electrophoretic display device of the present embodiment, the first afterimage erasing step and the second afterimage erasing step use the partial drive format, and an image other than a single-color display is employed as a predetermined image. In, for example, a checkered pattern of several dots including the first color and the second color, the direction of the electric field is different during driving for every several dots. When a normal display and an inverse display are executed using an image of a checkered pattern, there is the possibility of being able to enhance the effect of erasing the afterimage in comparison to a case where a single-color display is used. In the present embodiment, an image other than a single-color display is used in order to enhance the effect of afterimage erasing.
The understanding herein is that, for example, the portion that is black in the checkered pattern in
A display example of the present embodiment shall now be described, with reference to
In a case where the predetermined change in temperature is detected after the first image display step and before the first image erasing step, a drive pulse signal that has been adjusted for the temperature after the change (TP4) is used to execute the first afterimage erasing step of
At this time, following the execution of the first afterimage erasing step and the second afterimage erasing step, the display will be black, as in
As per the foregoing, in the method for driving an electrophoretic display device of the present embodiment, too, it is possible to compensate also for the effects of a change in temperature (more specifically, an afterimage such as in
The flow chart in
The other steps are the same as the steps to which like reference numerals were assigned in
In this manner, in the method for driving an electrophoretic display device in the present embodiment, a DC balance is struck irrespective of whether or not there has been a change in temperature, and in a case where a change in temperature has taken place, then the afterimage caused by the change in temperature is erased by the execution of the first afterimage erasing step and the second afterimage erasing step in which the drive pulse signal that has been adjusted on the basis of the temperature after the change is used. At this time, there can be expected to be a higher effect of afterimage erasing. For this reason, the long-term reliability can be ensured, and the display quality is further enhanced. Also, because the partial drive format is still used, it is possible to shorten the refresh time for an image in comparison to a case where solely the full-screen drive format is used.
An application example of the invention shall now be described with reference to
The CPU 2 controls the other blocks and carries out a variety of computations and processes. The CPU 2 can, for example, read a program from the storage unit 5 and input a time signal or the like to the electrophoretic display device 10 in conformity with the program.
The input unit 4 can, for example, accept an instruction from a user of the electronic apparatus 1 and output a signal corresponding to the instruction to the other blocks.
The storage unit 5 can, for example, be a memory such as a DRAM or SRAM, or can include a read-only memory (ROM). The program used by the CPU 2 can, for example, be written onto the ROM included by the storage unit 5.
The display unit 3 is a part of the electrophoretic display device 10 and can, for example, display the time, or display text, pictures, or the like.
By including the electrophoretic display device 10 of the first or second embodiment, the electronic apparatus 1 is able to erase the afterimage that can be produced in a case where a change in temperature has occurred, while still striking a DC balance. For this reason, an electronic apparatus 1 of excellent long-term reliability and favorable display quality can be realized.
The electrophoretic display device of the first and second embodiments can be applied to a variety of electronic apparatuses, which include these specific examples. The electronic apparatus of such description, by striking a DC balance, can ensure the long-term stability of the display unit, and is also able to enhance the display quality because the afterimage that can be produced in a case where a change in temperature has occurred is erased.
In the embodiments above, the electrophoretic display device is not limited to being one where a black-and-white two-particle system based on black particles and white particles is electrophoresed; instead, a single-particle system of blue-white can be electrophoresed, or color combinations other than black and white can be used.
There is also no limitation to being an electrophoretic display device; the method of driving described above can also instead be applied to a displaying means having the memory property. Examples include an electrochromic display (ECD), a ferroelectric liquid crystal display, a cholestric liquid crystal display, and the like.
The electronic timepiece of the application example described above is also not limited to being a wristwatch; application to a broad range of apparatuses having a timepiece function is possible, including a table clock, a wall clock, a pocket watch, and the like.
There is no limitation to these illustrative examples, and the invention includes any configuration substantially identical to a configuration described in the embodiments (for example, a configuration of identical functions, methods, and results, or a configuration of identical objectives and effects). The invention also includes any configuration in which the non-essential portions of a configuration described in the embodiments have been replaced. The invention further includes any configuration giving rise to the same effects as those of a configuration described in the embodiments, or any configuration making it possible to achieve the same objectives. The invention moreover includes any configuration obtained when a well-known feature is added to a configuration described in the embodiments.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-199616 | Sep 2012 | JP | national |
