JP4623429B2 - Electrophoretic display device, electronic apparatus, driving method of electrophoretic display device, and controller - Google Patents

Description

  The present invention relates to an electrophoretic display device and an electronic apparatus.

  An electrophoretic display device is configured by sealing an electrophoretic dispersion liquid containing one or more kinds of electrophoretic particles and an electrophoretic dispersion medium between a pair of counter electrode plates, at least one of which is transparent. The When a voltage is applied between the two electrodes, the electrophoretic particles move in the electrophoretic dispersion medium, and the distribution thereof changes, so that the optical reflection characteristics change and information can be displayed.

  In Patent Document 1, in an active matrix electrophoretic display device using electronic ink, when changing display contents, all pixel electrodes are set to the same potential, and a voltage is applied between the common electrode and the pixel electrode. A driving method that can suppress the drive voltage and prevent erroneous rewriting by erasing all the display area that has been displayed by applying the voltage and then displaying new display contents thereafter is disclosed. Has been.

JP 2002-149115 A

  However, according to the driving method described above, an afterimage tends to remain on the display unit. The afterimage in this case includes an afterimage at the time of erasing that occurs at the time of image switching and a temporally afterimage that occurs by repeatedly applying a voltage to the electrophoretic display element.

  Therefore, an object of the present invention is to reduce the afterimage of the electrophoretic display device.

  The electrophoretic display device according to the present invention includes a display unit including a plurality of pixels, a pixel electrode formed in each of the plurality of pixels, a common electrode facing the plurality of pixel electrodes, the pixel electrode, An electrophoretic particle disposed between the common electrode and a control unit configured to form an image by moving the electrophoretic particle by controlling a voltage signal applied to the common electrode and the pixel electrode. The control unit converts an image displayed on the display unit from a first image including a first gradation region and a second gradation region, a first gradation region, and a second gradation region. In the switching period for changing to the second image including the gradation region, there is provided a period in which the entire display unit is set to the first gradation and a period in which the entire display unit is set to the second gradation, and the switching is performed. Before the display portion is set to the first gradation in the period A voltage signal applied to the common electrode and the pixel electrode is controlled so that the amount of movement of the electrophoretic particles is equal to the amount of movement of the electrophoretic particles for setting the display unit to the second gradation. It is.

  Thereby, in the switching period, it is relieved that the same voltage is repeatedly applied to the electrophoretic element and the same gradation is continuously displayed, and an afterimage due to a decrease in retention characteristics after the voltage interruption of the electrophoretic particles can be reduced. .

Further, it is preferable that the control unit performs control so as to provide a period for setting the display unit to the first gradation immediately before displaying the second image on the display unit in the switching period.
Thereby, the flicker at the time of image switching can be eliminated.

Further, it is preferable that the control unit provides a period in which the display unit is alternately set to the first gradation and the second gradation in the switching period with a period of 1 millisecond to 10 milliseconds.
As a result, the electrophoretic particles are well stirred in the dispersion system, and the afterimage can be reduced.

In addition, the electrophoretic display device of the present invention includes, for example, first particles that form the first gradation image and second particles that form the second gradation image. The first particles and the second particles have different charges, and the control unit has the same moving amount of the first particles and the moving amount of the second particles in the switching period. The voltage is controlled so that
Thereby, it is possible to reduce the deterioration of the contrast between the first gradation and the second gradation with time.

  In the electrophoretic display device of the present invention, for example, the mobility in the electric field of the first particle and the second particle is equal, and the control unit includes a first electrode connected to the common electrode in the switching period. Control is performed so that the time for applying the voltage and applying the second voltage to the pixel electrode is equal to the time for applying the second voltage to the common electrode and applying the first voltage to the pixel electrode. To do.

The electronic device according to the present invention includes all devices including the above-described electrophoretic display device as a display unit, and includes a display device, a television device, an electronic book, an electronic paper, a clock, a calculator, a mobile phone, and portable information. Includes terminals. Also, things that deviate from the concept of “equipment”, for example, flexible paper / film-like objects, belonging to real estate such as wall surfaces to which these objects are attached, moving objects such as vehicles, flying objects, ships, etc. Including those belonging to.
The driving method of the electrophoretic display device according to the present invention includes a display unit including a plurality of pixels, a pixel electrode formed in each of the plurality of pixels, a common electrode facing the plurality of pixel electrodes, and the pixel An electrophoretic display device comprising: an electrophoretic particle disposed between an electrode and the common electrode, wherein an image displayed on the display unit includes a first gradation region and a first gradation region. In the switching period in which the first image including the second gradation region is changed to the second image including the first gradation region and the second gradation region, the entire display unit is Providing a period of gradation and a period of changing the entire display unit to the second gradation, and, in the switching period, the amount of movement of the electrophoretic particles for setting the display unit to the first gradation; The amount of movement of the electrophoretic particles for making the display unit the second gradation is equal. So as to, and controls the voltage signal applied to the common electrode and the pixel electrode.
The controller according to the present invention includes a display unit including a plurality of pixels, a pixel electrode formed in each of the plurality of pixels, a common electrode facing the plurality of pixel electrodes, the pixel electrode, and the common electrode. A controller for controlling an electrophoretic display device having an electrophoretic particle disposed between the first gradation region and the second floor. In the switching period for changing from the first image including the tone area to the second image including the first gradation area and the second gradation area, the entire display unit is changed to the first gradation. A period during which the entire display unit is set to the second gradation, and a movement amount of the electrophoretic particles for setting the display unit to the first gradation during the switching period, and the display unit The amount of movement of the electrophoretic particles for making the second gradation So properly, and controls the voltage signal applied to the common electrode and the pixel electrode.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a diagram showing an overall electrical configuration of the electrophoretic display device 10 according to the first embodiment. The electrophoretic display panel A (display unit) includes a plurality of pixels, and these pixels include a TFT (Thin Film Transistor) 103 as a switching element, which will be described later, and a pixel electrode 104 connected to the TFT 103. It consists of On the other hand, a scanning line driving circuit 130 and a data line driving circuit 140 are formed in the peripheral region of the element substrate 100. In the electrophoretic display panel A of the element substrate 100, a plurality of scanning lines 101 are formed in parallel along the X direction shown in the drawing. In addition, a plurality of data lines 102 are formed in parallel along the Y direction orthogonal thereto. Each pixel is arranged in a matrix corresponding to the intersection of the scanning line 101 and the data line 102.

  A controller (control unit) 300 is provided in the peripheral circuit of the electrophoresis apparatus. The controller 300 includes an image signal processing circuit and a timing generator. Here, the image signal processing circuit generates image data and a counter electrode control signal, and inputs them to the data line driving circuit 140 and the counter electrode modulation circuit 150, respectively. The counter electrode modulation circuit 150 supplies a bias signal Vcom and a power supply voltage Vs to the common electrode of the pixel and the counter electrode of the storage capacitor, respectively. For example, image reset is set by a bias signal Vcom (reset signal) having a predetermined positive or negative level. The reset signal is output for a predetermined period before the data line driving circuit 140 outputs image data. The reset is used to attract the electrophoretic particles migrating in the dispersion medium to the pixel electrode or the common electrode to initialize the spatial state. The timing generator generates various timing signals for controlling the scanning line driving circuit 130 and the data line driving circuit 140 when reset settings and image data are output from the image signal processing circuit.

  FIG. 2 is a diagram illustrating the structure of each pixel of the electrophoretic display device 10. The pixel (i, j) in the i-th row and the j-th column includes the TFT 103, the pixel electrode 104, and the storage capacitor Cs. A gate terminal of the TFT 103 is connected to the scanning line 101, and a source terminal thereof is connected to the data line 102. Further, the drain terminal of the TFT 103 is connected to the pixel electrode 104 and the storage capacitor Cs. The holding capacitor Cs holds the voltage applied to the pixel electrode 104 by the TFT 103. Since the pixel is configured by sandwiching an electrophoretic layer between the pixel electrode 104 and the common electrode Com, a pixel capacitance Cepd is formed according to the electrode area, the distance between the electrodes, and the dielectric constant of the electrophoretic layer. is doing. The common electrode Com is connected to the counter electrode modulation circuit 150 via the wiring 201. The other side of the storage capacitor Cs is connected to the storage capacitor line 106. The storage capacitor line 106 is connected to the power source Vs by the counter electrode modulation circuit 150.

Regarding the driving of the electrophoretic display device 10, the reset operation will be described first. At the reset timing, when the scanning line driving circuit 130 outputs a selection signal to all the scanning lines 101 and all the scanning line signals become active, the TFTs 103 connected to all the pixels connected to these scanning lines 101 are turned on. It becomes a state. At this time, the data line driving circuit 140 outputs a high level or a low level to all data lines. This signal is supplied to all the pixel electrodes. The counter electrode modulation circuit 150 supplies the common electrode Com with a low level when a high level is supplied to all the data lines, and supplies a high level signal when a low level is supplied to all the data lines. To do. At this time, since the same potential difference is applied between the pixel electrode and the common electrode of all the pixels, the electrophoretic display element is reset to the first gradation or the second gradation in all the pixel regions. The
Next, an image writing operation will be described. During the image writing operation, the scanning line driving circuit 130 sequentially supplies a selection signal to the scanning line 101. When the selection signal is supplied to the j-th scanning line 101 and the selection is made, the TFT 103 connected to the scanning line 101 is turned on. At this time, the data signal Xi (image signal) supplied from the data line driving circuit 140 is written to the pixel electrode 104 in synchronization with the scanning line selection. At this time, the storage capacitor Cs is also charged at the voltage level of the data signal Xi, and even after the TFT 103 is cut off, the charge of the pixels (pixel electrode and common electrode) is maintained to maintain the image by the electrophoretic particles. Each pixel performs display in accordance with the voltage level of the data signal, thereby displaying an image.

Next, a detailed operation when changing the display image during the operation of the electrophoretic display device 10 will be described. First, a mechanism for generating an afterimage in the electrophoretic display device of the comparative example will be described.
FIG. 3 is a diagram illustrating an afterimage of the electrophoretic display device of the comparative example. FIG. 4 is a timing chart showing a method of controlling the voltage applied to the common electrode and the pixel electrode by the controller of the electrophoretic display device of the comparative example. FIG. 5 is a diagram schematically showing the operation when changing the display image of the electrophoretic display device of the comparative example.

The afterimage at the time of erasure and the afterimage over time will be described with reference to FIGS.
Here, the electrophoretic particles include negatively charged white electrophoretic particles (first particles) and positively charged black electrophoretic particles (second particles). Also, let white be the first gradation and black be the second gradation.

  In the state of FIG. 3A, the character “H” in the second gradation (black) is displayed on the display section on the background of the first gradation (white). Here, the region of the character “H” is defined as region a, and the other background region is defined as region b. Immediately before “H” is written, the entire display section is displayed in white. When “H” is written, a second voltage (low level) is applied to the common electrode as shown in FIG. Further, the first voltage (high level) is applied only to the pixel electrode corresponding to the region a, and the second voltage (low level) is applied to the pixel electrode corresponding to the background region b. As a result, as shown in FIG. 5A, the black electrophoretic particles positively charged only in the region a move to the common electrode side, and the white electrophoretic particles negatively charged move to the pixel electrode side. Characters are displayed. After writing the letter “H”, the second voltage (low level) is applied to the common electrode and all the pixel electrodes, and the display content is retained.

  Next, in the state of FIG. 3B, before changing the display image, the entire display unit is displayed in white to erase the image. When erasing an image, as shown in FIG. 4, a first voltage (high level) is applied to the common electrode, and a second voltage (low level) is applied to all the pixel electrodes. As a result, as shown in FIG. 5B, the black electrophoretic particles move to the pixel electrode side in the region a, and the entire display portion becomes white.

  At this time, as shown in FIG. 3B, the region a is white with a lower reflectance than the region b, that is, white near gray, forming an afterimage. This is because, although the initial distribution state of the electrophoretic particles is different between the region a and the region b, the same electric field is applied to the region a and the region b for the same time, so that there is a difference in the amount of movement of the electrophoretic particles. This is because there is a slight difference in gradation.

  Next, in the state of FIG. 3C, the letter “I” is displayed on the display unit with the second gradation (black) on the first gradation (white) background. Here, the area of the character “I” is defined as area c. When "I" is written, the second voltage (low level) is applied to the common electrode as shown in FIG. Further, the first voltage (high level) is applied to the pixel electrode corresponding to the region c, and the second voltage (low level) is applied to the pixel electrodes corresponding to the other regions. As a result, as shown in FIG. 5C, the black electrophoretic particles positively charged only in the region c move to the common electrode side, and the letter “I” is displayed.

  At this time, as shown in FIG. 3C, the portion of the character “H” displayed before remains as a light gray afterimage. Such an afterimage generated at the time of image switching is called an afterimage at the time of erasure.

After writing the letter “I”, the second voltage (low level) is applied to the common electrode and all the pixel electrodes as shown in FIG. 5D, and the display contents are displayed as shown in FIG. Is retained.
At this time, in the state of FIG. 3D, the region b is white with a low reflectance compared to the state of FIG. This is due to a temporal afterimage that occurs when a voltage is repeatedly applied to the electrophoretic element.

If the same voltage is repeatedly applied to a certain part of the electrophoretic element to continuously display the same gradation, the retention characteristics of the electrophoretic particles when the voltage application is interrupted are deteriorated. If the retention property of the electrophoretic particles is lowered, as shown in FIG. 5D, the electrophoretic particles may move slightly when an electric field is not applied to the electrophoretic element, and the contrast of the image may deteriorate.
That is, if a voltage for writing white is continuously applied in an area displaying white, when the voltage is not applied, white having a low reflectivity, that is, white close to gray is obtained.

  In the state of FIG. 5B, the voltage applied to write white is excessive in the electrophoretic element corresponding to the region b compared to the region a. When such voltage application is repeated, the retention characteristics of the electrophoretic particles in the region b when the voltage application is interrupted are lowered, and an afterimage with time is generated in the region b as shown in FIG. become.

  Such a temporal afterimage is eliminated by applying a voltage for refreshing every several tens of minutes to several hours, but frequent refreshing operation has a problem of increasing power consumption.

Next, the operation when changing the display image of the electrophoretic display device 10 according to the present invention will be described.
FIG. 6 is a timing chart showing a method of controlling the voltage applied to the common electrode and the pixel electrode by the controller 300 of the electrophoretic display device 10 according to the first embodiment of the invention.
The difference from FIG. 4 is the control method in the erasing time (switching period) during rewriting from the image (first image) “H” before the change to the image (second image) “I” after the change. .
As shown in the figure, in the electrophoretic display device 10 according to the present invention, the first voltage is applied to the common electrode in order to perform the all white (first gradation) display immediately before displaying the changed image in the erasing time. (High level) is applied, and the second voltage (low level) is applied to all the pixel electrodes.

  Furthermore, in the electrophoretic display device 10, in order to display the entire display portion in black (second gradation) before performing the all white display, the second voltage is applied to the common electrode, and the first voltage is applied to all the pixel electrodes. A voltage is applied. Here, the voltage application time for making all white is equal to the voltage application time for making all black. In addition, about 100 milliseconds-1000 milliseconds are suitable for the voltage application time for making it all white, and the voltage application time for making it all black.

  The reason why the voltage application time for making all white is equal to the voltage application time for making all black is that the mobility of the black electrophoretic particles and the white electrophoretic particles in the electric field is equal. Here, the mobility of the electrophoretic particles in the electric field being equal means that the distance of movement of the electrophoretic particles is equal when an electric field having a certain strength is applied to the electrophoretic particles for a certain period of time. The mobility of the electrophoretic particles in the electric field is determined by the charge, weight, and viscosity of the solvent in which the electrophoretic particles are dispersed.

Here, the mobility of the black electrophoretic particles is μ _B , the mobility of the white electrophoretic particles is μ _W , the electric field strength is E, and the voltage for moving the black electrophoretic particles to the display side (here, the common electrode side). When the application time is T _B and the voltage application time for moving the white electrophoretic particles to the display side is T _W , the movement amount D of each electrophoretic particle can be expressed by the following equation.

Therefore, if the mobility of each electrophoretic particle is equal to the product of the voltage application time for moving each electrophoretic particle to the display side, the amount of movement of both electrophoretic particles becomes equal. Here, in the first embodiment, if the mobility of the black electrophoretic particles is μ _B and the mobility of the white electrophoretic particles is equal to μ _W , the display portion is completely white in the erasing period shown in FIG. By making the voltage application time for making it equal to the voltage application time for making all black, the amount of movement of both electrophoretic particles in the erasing period becomes equal.

  As a result, the accumulation of the erasing operation alleviates the fact that the same voltage is repeatedly applied to the electrophoretic element and the same gradation continues to be displayed, resulting in an excessive writing state and the retention of the electrophoretic particles being reduced. It is possible to reduce the afterimage after time after the application is cut off.

FIG. 7 is a timing chart showing a method of controlling the voltage applied to the common electrode and the pixel electrode by the controller 300 of the electrophoretic display device 10 according to the first embodiment of the invention.
In the example of FIG. 7, in order to perform all white (first gradation) display immediately before displaying the changed image in the erasing time, the first voltage (high level) is applied to the common electrode, and all pixels are displayed. The second voltage (low level) is applied to the electrode as in the example of FIG.

  In the example of FIG. 7, all white display and all black display are repeated in a short time before displaying all white. Here, if the mobility of each electrophoretic particle is equal, the sum of the voltage application time for making it all white and the voltage application time for making it all black are equal. It is appropriate to repeat the all white display and the all black display with a period of about 1 to 10 milliseconds.

  As in the example shown in FIG. 7, by repeating the all white display and the all black display in a short time before performing the all white display, the electrophoretic particles are well stirred in the dispersion medium, the afterimage at the time of erasure, and the time-lapse Afterimage can be reduced.

  Also, as shown in the timing charts of FIGS. 8 and 9, long all white / all black (about 100 to 1000 milliseconds) and short all white and all black (about 1 to 10 milliseconds) are combined. The same effect can be obtained by controlling in this way.

  As described above, in the erasing period, all white (first gradation) display is performed immediately before displaying the changed image, and the first gradation or second gradation is displayed in the previous period. This is performed multiple times alternately, and the afterimage during erasure and the afterimage over time are reduced by controlling the applied voltage and voltage application time so that the total amount of movement of the white and black electrophoretic particles in the erasure period is equal. can do.

Electronic Device FIG. 10 is a perspective view illustrating a specific example of an electronic device to which the electrophoretic display device of the present invention is applied. FIG. 10A is a perspective view illustrating an electronic book that is an example of the electronic apparatus. The electronic book 1000 includes a book-shaped frame 1001, a cover 1002 that can be rotated (openable and closable) with respect to the frame 1001, an operation unit 1003, and the electrophoretic display device of the present invention. Display unit 1004.

  FIG. 10B is a perspective view illustrating a wrist watch that is an example of the electronic apparatus. The wristwatch 1100 includes a display unit 1101 configured by the electrophoretic display device of the present invention.

  FIG. 10C is a perspective view illustrating electronic paper which is an example of the electronic apparatus. This electronic paper 1200 includes a main body portion 1201 formed of a rewritable sheet having the same texture and flexibility as paper, and a display portion 1202 formed of an electrophoretic display device of the present invention.

For example, electronic books, electronic papers, and the like are supposed to be used for repeatedly writing characters on a white background, and therefore it is necessary to eliminate afterimages at the time of erasure and afterimages over time.
Note that the range of electronic devices to which the electrophoretic display device of the present invention can be applied is not limited to this, and includes a wide range of devices that utilize changes in visual color tone accompanying the movement of charged particles.

FIG. 1 is a diagram showing an overall electrical configuration of an electrophoretic display device according to Embodiment 1 of the present invention. FIG. 2 is a diagram illustrating the structure of each pixel of the electrophoretic display device. FIG. 3 is a diagram illustrating an afterimage of the electrophoretic display device of the comparative example. FIG. 4 is a timing chart illustrating a method for controlling the voltage applied to the common electrode and the pixel electrode of the electrophoretic display device of the comparative example. FIG. 5 is a diagram schematically showing the operation when changing the display image of the electrophoretic display device of the comparative example. FIG. 6 is an example of a timing chart showing a method for controlling the voltage applied to the common electrode and the pixel electrode of the electrophoretic display device of the electrophoretic display device according to the first embodiment of the present invention. FIG. 7 is an example of a timing chart showing a method for controlling the voltage applied to the common electrode and the pixel electrode of the electrophoretic display device of the electrophoretic display device according to the first embodiment of the present invention. FIG. 8 is an example of a timing chart showing a method for controlling the voltage applied to the common electrode and the pixel electrode of the electrophoretic display device of the electrophoretic display device according to the first embodiment of the present invention. FIG. 9 is an example of a timing chart showing a method for controlling the voltage applied to the common electrode and the pixel electrode of the electrophoretic display device of the electrophoretic display device according to the first embodiment of the present invention. 10A to 10C are diagrams showing examples of electronic devices according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electrophoretic display apparatus, 100 element board | substrate, 101 scanning line, 102 data line, 103 TFT, 104 pixel electrode, 106 holding capacity line, 130 scanning line drive circuit, 140 data line drive circuit, 150 counter electrode modulation circuit, 201 wiring 300 controller

Claims (8)

A display unit including a plurality of pixels;
A pixel electrode formed on each of the plurality of pixels;
A common electrode facing the plurality of pixel electrodes;
Electrophoretic particles disposed between the pixel electrode and the common electrode;
Wherein by controlling a voltage signal applied to the common electrode and the pixel electrode, and a control unit for forming an image by moving the electrophoretic particles,
The controller is
The image displayed on the display unit includes a first gradation area and a second gradation area from a first image including a first gradation area and a second gradation area. In the switching period for changing to the second image, a period for setting the entire display section to the first gradation and a period for setting the entire display section to the second gradation are provided.
In the switching period, the amount of movement of the electrophoretic particles for setting the display portion to the first gradation is equal to the amount of movement of the electrophoretic particles for setting the display portion to the second gradation. As described above, an electrophoretic display device that controls voltage signals applied to the common electrode and the pixel electrode.   2. The control unit according to claim 1, wherein the control unit performs control so as to provide a period during which the display unit is set to a first gradation immediately before displaying the second image on the display unit in the switching period. The electrophoretic display device described in 1.   The control unit includes a period in which the display unit is alternately set to the first gradation and the second gradation in a period of 1 millisecond to 10 milliseconds in the switching period. The electrophoretic display device according to claim 1 or 2. The electrophoretic particles include first particles that form the first gradation image and second particles that form the second gradation image, and the first particles and the second particles. Particles have different charges,
The control unit controls the application voltage or the voltage application time of the voltage signal so that the movement amount of the first particles and the movement amount of the second particles become equal during the switching period. The electrophoretic display device according to claim 1. The mobility of the first particles and the second particles in the electric field is equal,
The control unit applies a first voltage to the common electrode, applies a second voltage to the pixel electrode, and applies a second voltage to the common electrode in the switching period, The electrophoretic display device according to claim 4, wherein the time for applying the first voltage to the electrodes is controlled to be equal.   An electronic apparatus comprising the electrophoretic display device according to any one of claims 1 to 5.   A display unit including a plurality of pixels; a pixel electrode formed on each of the plurality of pixels; a common electrode opposed to the plurality of pixel electrodes; and an electricity disposed between the pixel electrode and the common electrode A method for driving an electrophoretic display device comprising electrophoretic particles,
  The image displayed on the display unit includes a first gradation area and a second gradation area from a first image including a first gradation area and a second gradation area. In the switching period for changing to the second image, a period for setting the entire display unit to the first gradation and a period for setting the entire display unit to the second gradation are provided.
  In the switching period, the amount of movement of the electrophoretic particles for setting the display portion to the first gradation is equal to the amount of movement of the electrophoretic particles for setting the display portion to the second gradation. Thus, the voltage signal applied to the common electrode and the pixel electrode is controlled. A display unit including a plurality of pixels; a pixel electrode formed on each of the plurality of pixels; a common electrode opposed to the plurality of pixel electrodes; and an electricity disposed between the pixel electrode and the common electrode A controller for controlling an electrophoretic display device comprising electrophoretic particles,
The image displayed on the display unit includes a first gradation area and a second gradation area from a first image including a first gradation area and a second gradation area. In the switching period for changing to the second image, a period for setting the entire display section to the first gradation and a period for setting the entire display section to the second gradation are provided.
In the switching period, the amount of movement of the electrophoretic particles for setting the display portion to the first gradation is equal to the amount of movement of the electrophoretic particles for setting the display portion to the second gradation. As described above, the controller controls a voltage signal applied to the common electrode and the pixel electrode .

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