JP2017194609A - Electrophoretic display device and drive method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrophoretic display device capable of maintaining a DC balance and displaying an image with high contrast while reducing an afterimage or flickers, and a drive method of the device.SOLUTION: A display device is provided, which includes: a display panel which has charge particles sealed between a pair of substrates having an electrode on each of opposing surfaces, displays an image by the movement of the charge particles and has memory property; and drive means for receiving a display data and applying a drive voltage to the electrodes of the display panel. The drive means applies a predetermined drive voltage pattern when displaying an image in the same gradation as that of an image previously displayed, where the predetermined drive voltage pattern includes an adjusting pulse and a writing pulse; and the adjusting pulse includes a first waveform in an opposite polarity to the writing pulse and having a lower absolute voltage than that of the writing pulse. Thereby, changes in the lightness of the display device during applying the predetermined drive voltage pattern are controlled to a predetermined value or less, which results in a DC balance between the adjusting pulse and the writing pulse.SELECTED DRAWING: Figure 7A

Description

  The present invention relates to a low power consumption display device and a driving method including a display panel having a memory property for performing display by movement of charged particles.

  Conventionally, as thin display devices, liquid crystal display devices have been widely used in various electronic devices, and in recent years, they have also been used as large color displays such as computers and televisions. Plasma displays are also used as large color displays for televisions. However, although liquid crystal display devices and plasma displays are much thinner than CRT display devices, they are still not thin enough for some applications and cannot be bent. Moreover, when using as a display of a portable device, further reduction of power consumption is desired.

  Therefore, as a display device that realizes further thinning and low power consumption, a display panel called an electronic paper using an electrophoretic display element has been developed. An electronic book, an electronic newspaper, an electronic advertisement signboard, and a guidance display board are developed. Attempts have been made to use it. A display panel (display device) using an electrophoretic display element (EPD) includes an image display layer in which charged particles are sealed between a pair of substrates each having an electrode on an opposing surface. In accordance with the polarity of the voltage applied between the electrodes of the substrate, the charged particles move by electrophoresis and display is performed.

  This electrophoretic display panel has a memory property because the charged particles do not move even if the driving voltage applied between the electrodes is removed, and the display state can be maintained even when the driving power is zero. The display period in which this display state is maintained may last from several seconds to several hours or months. For this reason, since this electrophoretic display panel can be driven with extremely little power, it is promising as a display device for portable devices such as wrist watches and mobile phones that require low power consumption. The electrophoretic element includes, for example, black particles and white particles as the electrophoretic particles, and these two kinds of particles are selectively attracted to the counter electrode side for each pixel, so that two gradations of black or white are obtained. Is displayed. In such an electrophoretic display device, an image is displayed by supplying a data potential corresponding to a gradation to be displayed to a pixel electrode provided in each of a plurality of pixels. For example, a positive electrode potential VSH (for example, +15 V) higher than the potential of the counter electrode (for example, 0 V) is supplied as a data potential to the pixel electrode of a pixel for displaying black, and at the same time, An image is displayed on the pixel electrode by supplying a negative potential −VSH (for example, −15 V) lower than the potential of the counter electrode.

As such an electrophoretic display device, each of a plurality of pixels arranged in a matrix corresponding to the intersection of a plurality of scanning lines and a plurality of data lines intersecting each other has one TFT ( An active matrix driving type electrophoretic display device including a pixel circuit (a so-called 1T1C type pixel circuit) configured to include a thin film transistor and a single capacitor (that is, a storage capacitor) that functions as a memory circuit. is there. During operation of such an active matrix drive type electrophoretic display device, a plurality of scanning lines are sequentially selected for each horizontal scanning period, and a data potential is applied to the pixels corresponding to the selected scanning lines via the data lines. Supplied.
In addition, as an electrophoretic display device, there is a segment method in which wiring having the same pattern as a desired image is created in advance, and display is thereby performed.

  In such an electrophoretic display panel, if a display voltage is black or white by applying a driving voltage and then no voltage is applied for a long time, a slight but free flow occurs in the charged particles in the display layer. However, there is a problem that the display density of white or black tends to change and approaches gray, and the contrast of the display gradually decreases to deteriorate visibility. Since the decrease in contrast due to the elapsed time deteriorates the display quality of the display panel, improvement is demanded.

  Further, when such an electrophoretic display panel is rewritten, a brightness difference may occur in the display image between a portion where rewriting is performed and a portion where rewriting is not performed. FIG. 4 shows an example of a display image, and FIG. 5 shows a driving waveform and a change in brightness at that time. The image (a) immediately after writing in FIG. 4 shows immediately after writing the previous image, the image before rewriting (b) is just before the image is rewritten after a certain time has passed, and the image (c) after partial rewriting is a partial This is the image after rewriting.

  The display area (1) and the display area (3) in FIG. 4 are portions where white and black are not rewritten. The display area (2) is a portion rewritten from white to black, and the display area (4) is a portion rewritten from black to white. Due to the lowering of the contrast, the newly rewritten images (display area (2) and display area (4)) are displayed more clearly than the images that have not been rewritten, and the display area (1) and The display area (3) may be recognized as an afterimage.

The above rewriting will be described with reference to FIGS. 5A to 5D from the viewpoint of the drive waveform and brightness of each display area. FIG. 5A shows a case where white display is maintained as in the display area (1). The drive waveform is maintained at 0 V, and the state in which the brightness is lowered by the L ^* drop d1 over time is maintained. FIG. 5B shows a case where black display is written in white display as in the display area (2). In order to maintain DC balance, white is written first and then black. FIG. 5C shows a case where a black display is maintained as in the display area (3). The drive waveform is maintained at 0 V, and the state in which the brightness is increased by L ^* rise d2 over time is maintained. FIG. 5D shows a case where white display is written in black display as in the display area (4). In order to maintain DC balance, black display is first written and then white display is written. As shown in FIGS. 5A to 5D, in the display areas (1) and (3) that are not rewritten, L ^* is changed by d1 or d2. On the other hand, in the display areas (2) and (4) with rewriting, there is no d1 and d2, and this difference is recognized as an afterimage.

  Up to this point, an example has been shown in which the gradation display of binary display of white and black is not performed. However, when the gradation display is performed, the contrast is lowered and the display density of the pixel is changed. Sometimes, when a driving voltage for rewriting the display is applied to the pixel electrode, the normal black display or white display density is not displayed, the display density varies, and the display quality deteriorates. . Such a phenomenon is also called an afterimage phenomenon and is one problem of the electrophoretic display panel.

As a countermeasure, there is a refresh driving method in which the entire display area is once displayed in black or white and the influence of the previously displayed image is removed. FIG. 6A shows an example of changes in brightness and drive waveforms when refreshing. In FIG. 6A, −15V is first applied to change the pixel to white display, and then + 15V is applied to return to black display again. By displaying black after displaying white once, the DC balance can be maintained and the L ^* rise d2 over time can be eliminated, but the screen will flicker white and black. When refreshing is performed as described above, since the brightness change of the display screen is large, it is recognized as flickering by the observer, which causes discomfort and discomfort.

  As another countermeasure, there is a method of overwriting the previously displayed image and erasing d2 even when the image does not change as shown in FIG. 6B. In FIG. 6B, + 15V is applied. d2 is deleted.

  However, when such driving is performed, the electric field applied between the electrodes of the electrophoretic display panel may be biased depending on the state of the display image (for example, displaying only black). Say. The DC imbalance is a state in which the integrated value of the applied voltage and time does not match on the plus side and the minus side, and is also expressed as having a DC (direct current) component. In the DC unbalanced state, the charge of the electrophoretic element is biased, resulting in a decrease in contrast, a decrease in electrode adhesion, a decrease in long-term reliability, and the like. On the other hand, the case where the integrated value of the applied voltage and time coincides on the plus side and the minus side is called DC balance, and the electrophoretic element is required to have DC balance among the individual write waveforms. .

  In Patent Document 1, by controlling the applied voltage and the applied time (number of frames) in the drive waveform, the DC balance is maintained and a color different from the final written image (black display or black display for white display). If this is the case, a drive method for temporarily displaying a white display is proposed. When the above method is used, refresh can be performed while maintaining DC balance, and afterimages can be reduced. However, countermeasures against flickering of the screen accompanying refresh are insufficient, and there is a possibility that flickering will be visually recognized.

  Patent Document 2 proposes a method for eliminating DC imbalance without changing the display image by applying a voltage equal to or lower than the threshold value at which the electrophoretic element operates to the polarity opposite to that of the display image. According to the method of Patent Document 2, it is possible to reduce image sticking and display unevenness while suppressing flickering of an image. However, since the driving is performed in a range where the display image does not change, the effect of reducing the afterimage is insufficient. In addition, when driving with a voltage in a range where the display image does not change, there is a problem that the absolute value of the driving voltage becomes small and the application time necessary for maintaining the DC balance becomes very long. .

  As described above, while the demands for reducing afterimages, improving contrast, preventing flickering, and extending the service life are becoming strict, the configurations described in Patent Documents 1 and 2 have insufficient performance.

JP 2007-163987 A JP 2011-232594 A

  The present invention has been made in view of the above problems, and an electrophoretic display device capable of ensuring a DC balance and performing high-contrast display while reducing afterimages and flickering, and an electric display It is an object to provide a method for driving an electrophoretic display panel.

One embodiment of the present invention for solving the above problems is a display panel having a memory property in which charged particles are enclosed between a pair of substrates each having an electrode on an opposing surface, and display is performed by movement of the charged particles; Driving means for inputting display data and applying a driving voltage to the electrodes of the display panel, wherein the driving means performs predetermined driving when displaying the same gradation as the previously displayed image. A voltage pattern is applied, and the predetermined drive voltage pattern includes an adjustment pulse and a write pulse, and the adjustment pulse includes a first waveform having a polarity opposite to that of the write pulse and having a lower absolute voltage value than the write pulse. Thus, the brightness change of the display device during application of the predetermined drive voltage pattern is equal to or less than a predetermined value, and the adjustment pulse and the write pulse are in DC balance.

  The adjustment pulse may further include a second waveform having the same polarity as the write pulse and a shorter application time than the write pulse.

  The adjustment pulse may include a plurality of first waveforms and second waveforms.

Further, the fluctuation of the brightness L ^* of the display device during application of the predetermined drive voltage pattern is an average value {(maximum value + minimum value) / 2} of the maximum value and the minimum value of lightness that can be displayed by the display device. You may make it not straddle the median value of the brightness of a certain display apparatus.

  Further, the brightness change value, which is a value obtained by subtracting the minimum value from the maximum value of the brightness L * of the display device during application of the predetermined drive voltage pattern, may be 15 or less.

  In addition, when displaying the desired gradation on the display device, the driving means may display the desired gradation only once after displaying the lightness limit value.

  In another aspect of the present invention, a charged particle is sealed between a pair of substrates each having an electrode on an opposite surface, and a display panel having a memory property for performing display by movement of the charged particle, and display data is input. A display device comprising: a driving unit that applies a driving voltage to an electrode of a display panel. The driving unit executes a display device driving method, wherein the driving unit displays the same gradation as the previously displayed image. In this case, a predetermined drive voltage pattern is applied, and the predetermined drive voltage pattern includes an adjustment pulse and a write pulse, and the adjustment pulse has a polarity opposite to that of the write pulse and lower in absolute voltage than the write pulse. 1 is included, the change in brightness of the display device during application of the predetermined drive voltage pattern is less than the predetermined value, and the adjustment pulse and the write pulse are in DC balance. That is a driving method of a display device.

  The adjustment pulse may further include a second waveform having the same polarity as the write pulse and a shorter application time than the write pulse.

  According to the present invention, it is possible to provide an electrophoretic display device and a method for driving an electrophoretic display panel capable of ensuring DC balance and performing display with high contrast while reducing afterimages and flickering.

Plan view of an electrophoretic display device according to the present invention FIG. 2 is an equivalent circuit diagram illustrating an electrical configuration of a pixel according to the present invention. Sectional drawing of the electrophoretic display device which concerns on this invention Figure showing the image of the afterimage at the time of partial rewriting The figure which shows the conventional general drive waveform at the time of partial rewriting The figure which shows the conventional general drive waveform at the time of partial rewriting The figure which shows the conventional general drive waveform at the time of partial rewriting The figure which shows the conventional general drive waveform at the time of partial rewriting The figure which shows the example of the brightness change in the case of performing the conventional refresh, and a drive waveform The figure which shows the example of the brightness change at the time of rewriting by the conventional overwrite, and a drive waveform The figure which shows the drive waveform and brightness change which concern on this invention The figure which shows the drive waveform and brightness change which concern on this invention The figure which shows the drive waveform and brightness change which concern on this invention The figure which shows the drive waveform and brightness change which concern on this invention The figure which shows the drive waveform and brightness change which concern on this invention The figure which shows the drive waveform and brightness change which concern on this invention The figure which shows the drive waveform and brightness change which concern on this invention

  Hereinafter, an electrophoretic display device and a driving method thereof according to the present embodiment will be described with reference to the drawings. In the following embodiments, an active matrix driving type electrophoretic display device will be described as an example of the electro-optical device according to the present embodiment. However, it is also possible to use a passive type, a segment type, or the like. is there.

  FIG. 1 is a configuration diagram around a display unit of an electrophoretic display device 1 according to the present embodiment.

  In FIG. 1, an electrophoretic display device 1 according to this embodiment is an active matrix drive type electrophoretic display device, and includes a display unit 2, a controller 10, a scanning line driving circuit 60, a data line driving circuit 70, and the like. The common potential supply circuit 100 is provided. The controller 10 is connected to a display unit via a flexible cable 14, and the controller 10 includes a CPU 11, a memory 12, and the like.

  In FIG. 2, the pixel 20 includes a pixel switching transistor 24, a pixel electrode 21, a counter electrode 22, an electrophoretic element 23, and a storage capacitor 27.

  FIG. 2 shows an example of the pixel 20 in the i-th row and the j-th column. The display unit 2 includes m rows × n columns of pixels 20 arranged in a matrix (two-dimensional plane), and m scanning lines 40 (Y1, Y2,..., Yi,..., Ym). , N data lines 50 (X1, X2,..., Xj,..., Xn) are provided so as to intersect each other. Specifically, the m scanning lines 40 extend in the row direction (that is, the horizontal direction in FIG. 2), and the n data lines 50 correspond to the column direction (that is, the vertical direction in FIG. 2). ) Respectively. The pixels 20 are arranged corresponding to the intersections of the m scanning lines 40 and the n data lines 50.

  The controller 10 controls the operations of the data line driving circuit 70 and the common potential supply circuit 100 using the scanning line driving circuit 60, the CPU 11, the memory 12, and the like. For example, the controller 10 supplies timing signals such as a clock signal and a start pulse to each circuit.

  The scanning line driving circuit 60 sequentially supplies a scanning signal in a pulsed manner to each of the scanning lines Y1, Y2,..., Ym during a predetermined frame period under the control of the controller 10.

  The data line driving circuit 70 supplies a data potential to the data lines X1, X2,..., Xn under the control of the controller 10. The data potential is any one of a reference potential GND (for example, 0 V), a high potential VSH (for example, +15 V), or a low potential -VSH (for example, -15 V).

  The common potential supply circuit 100 supplies a common potential Vcom (in this embodiment, the same potential as the reference potential GND) to the common potential line 90. Note that the common potential Vcom is a range in which no voltage is substantially generated between the counter electrode 22 (see FIG. 2) supplied with the common potential Vcom and the pixel electrode 21 (see FIG. 2) supplied with the reference potential GND. Of these, a potential different from the reference potential GND may be used. For example, the common potential Vcom may be a value different from the reference potential GND supplied to the pixel electrode 21 in consideration of fluctuations in the potential of the pixel electrode 21 due to feedthrough.

  Here, the feed-through means that when the scanning signal is supplied to the scanning line 40 after the scanning signal is supplied to the scanning line 40 and the potential is supplied to the pixel electrode 21 via the data line 50 (for example, This refers to a phenomenon in which the potential of the pixel electrode 21 fluctuates due to parasitic capacitance with the scanning line 40 (for example, decreases with a decrease in the potential of the scanning line 40). The common potential Vcom may be set to a value slightly lower than the reference potential GND supplied to the pixel electrode 21 on the assumption that the potential of the pixel electrode 21 is lowered due to feedthrough.

  Note that various signals are input to and output from the controller 10, the scanning line driving circuit 60, the data line driving circuit 70, and the common potential supply circuit 100, but descriptions of those not particularly related to the present embodiment are omitted. .

  Since the controller 10 has the memory 12, it is possible to store a display before rewriting. In the present invention, an image before rewriting and a new rewritten image are compared, and writing can be performed with an optimum driving waveform.

  The pixel switching transistor 24 is composed of, for example, an N-type transistor. The pixel switching transistor 24 has a gate electrically connected to the scanning line 40, a source electrically connected to the data line 50, and a drain electrically connected to the pixel electrode 21 and the storage capacitor 27. It is connected to the. The pixel switching transistor 24 applies a data potential supplied from the data line driving circuit 70 via the data line 50 to a timing corresponding to a scanning signal supplied in a pulse form from the scanning line driving circuit 60 via the scanning line 40. Thus, the data is output to the pixel electrode 21 and the storage capacitor 27.

  A data potential is supplied to the pixel electrode 21 from the data line driving circuit 70 via the data line 50 and the pixel switching transistor 24. The pixel electrode 21 is disposed so as to face the counter electrode 22 via the electrophoretic element 23.

  The counter electrode 22 is electrically connected to a common potential line 90 to which a common potential Vcom is supplied.

  The electrophoretic element 23 is composed of a plurality of microcapsules 80 each forming an electrophoretic display material each containing an electrophoretic particle.

  The storage capacitor 27 is composed of a pair of electrodes arranged opposite to each other with a dielectric film therebetween, one electrode is electrically connected to the pixel electrode 21 and the pixel switching transistor 24, and the other electrode is a common potential line 90. Is electrically connected. The storage capacitor 27 can maintain the data potential for a certain period.

  Next, a specific configuration of the display unit of the electrophoretic display device according to the present embodiment will be described with reference to FIG.

  FIG. 3 is a partial cross-sectional view of the display unit 2 of the electrophoretic display device 1 according to this embodiment.

  In FIG. 3, the pixel 20 has a configuration in which a microcapsule 80 is sandwiched between a TFT substrate 28 and a counter substrate 29. In the present embodiment, description will be made on the assumption that an image is displayed on the counter substrate 29 side.

  The TFT substrate 28 is a substrate made of, for example, glass or plastic. Although not shown here, the pixel switching transistor 24, the storage capacitor 27, the scanning line 40, the data line 50, the common potential line 90, and the like described above with reference to FIG. 2 are formed on the TFT substrate 28. A laminated structure is formed. A plurality of pixel electrodes 21 are provided in a matrix on the upper layer side of the stacked structure.

  The counter substrate 29 is a transparent substrate made of, for example, glass or plastic. On the surface of the counter substrate 29 facing the TFT substrate 28, the counter electrode 22 is formed in a solid shape so as to face the plurality of pixel electrodes 21. The counter electrode 22 is made of a transparent conductive material such as magnesium silver (MgAg), indium / tin oxide (ITO), indium / zinc oxide (IZO).

  The electrophoretic element 23 is composed of a plurality of microcapsules 80 each containing electrophoretic particles, and is fixed between the TFT substrate 28 and the counter substrate 29 by a binder 30 and an adhesive layer 31 made of, for example, resin. . In the display unit 2 according to the present embodiment, in the manufacturing process, an electrophoretic sheet in which the electrophoretic element 23 is previously fixed to the counter substrate 29 side by the binder 30 is formed with a separately manufactured pixel electrode 21 and the like. The TFT substrate 28 is bonded to an adhesive layer 31.

  One or a plurality of microcapsules 80 are sandwiched between the pixel electrode 21 and the counter electrode 22, and are arranged in one pixel 20 (in other words, with respect to one pixel electrode 21).

  The microcapsule 80 has a capsule shell made of methacrylic acid resin, gum arabic, or the like, and white particles made of titanium oxide or zinc oxide and black particles made of carbon black, aniline black, etc. are highly viscous such as silicone oil. It is encapsulated in a dispersed state in a dispersion medium. For example, white particles are negatively charged, for example, black particles are positively charged.

  For this reason, the white particles and the black particles can move in the dispersion medium by the electric field generated by the potential difference between the pixel electrode 21 and the counter electrode 22.

  In FIG. 3, when a voltage is applied between the pixel electrode 21 and the counter electrode 22 so that the potential of the counter electrode 22 is relatively high, the positively charged black particles are microscopically affected by Coulomb force. While being attracted to the pixel electrode 21 side in the capsule 80, the negatively charged white particles are attracted to the counter electrode 22 side in the microcapsule 80 by the Coulomb force. As a result, white particles gather on the display surface side (that is, the counter electrode 22 side) in the microcapsule 80, and the color of the white particles (that is, white) is displayed on the display surface of the display unit 2. The Rukoto. On the contrary, when a voltage is applied between the pixel electrode 21 and the counter electrode 22 so that the potential of the pixel electrode 21 is relatively high, the negatively charged white particles are generated by the Coulomb force. While attracted to the 21 side, the positively charged black particles are attracted to the counter electrode 22 side by the Coulomb force. As a result, black particles gather on the display surface side of the microcapsule 80, and the color of the black particles (that is, black) is displayed on the display surface of the display unit 2.

  In addition, red, green, blue, etc. can be displayed by replacing the pigment used for white particle | grains and black particle | grains, for example with pigments, such as red, green, and blue.

  The above is a configuration for an active matrix type monochrome display using TFTs. However, within the spirit of the present invention, it is possible to appropriately change a display method such as a passive type or a segment type or a multi-color gradation display. .

Example 1
Although the Example of this invention is shown below, it is not necessarily limited to this. 7A and 7B show the drive waveform and brightness of the display image of the present invention. The example shown to FIG. 7A, 7B is a case where black is continuously displayed by the binary display of white and black. First, the waveform P1 will be described. Finally, in order to perform black display, a writing pulse is written at +15 V at time t1 (130 ms). As the previous stage, as the adjustment pulse, the adjustment pulse A is, for example, -3V (a negative voltage having an opposite attribute to that of the write pulse and the absolute value of the voltage is smaller than 15V) three times at time t2 (250 ms). Write. For the adjustment pulse B, the time t3 (10 ms) is written twice at + 15V. Here, the time integration value of the voltage indicated by the application time × voltage is expressed as S, the time integration of the write pulse is S1, the time integration of the adjustment pulse A is S2, and the time integration of the adjustment pulse B is S3. To do. Table 1 shows specific application time and voltage of each pulse. In the present invention, the drive waveform is set so that S1 + S2 + S3 = 0, and thereby the DC balance is maintained.

  Next, the lightness L1 when the waveform P1 is input will be described. L1 gradually increases in brightness while the adjustment pulse A is input, but the brightness decreases at the stage when the adjustment pulse B is input. Since the absolute value of the voltage of the adjustment pulse B is larger than that of the adjustment pulse A, the brightness can be lowered even if the application time is short. As shown in P1, by repeating the adjustment pulse A and the adjustment pulse B, the brightness of the display screen gradually increases and decreases. As a result, movement occurs in the electrophoretic particles and the particles are loosened, so that variations in the display image in the subsequent writing pulse are reduced. In addition, since the change in brightness during application of the adjustment pulse is small, there is little flickering on the screen, and it is difficult for the observer to feel uncomfortable. In addition, since the DC balance is maintained as the waveform, deterioration of the electrophoretic element can be suppressed. The above is described in the example of rewriting from black display to black display, but the same applies to the case of white display by changing the polarity of the pulse voltage.

  The absolute value of the voltage of the adjustment pulse A is preferably selected in accordance with the electrophoretic element, and is preferably selected in combination with the pulse width. However, when VSH is + 15V, it is 1V or more and 7.5V or less. 2V or more and 5V or less is more preferable. When the voltage absolute value of the adjustment pulse A is less than 1 V, the applied voltage is too low and the electrophoretic particles hardly operate, and the effect of loosening the particles in advance is reduced. Moreover, the application time required to maintain the DC balance increases, and the rewriting speed decreases. On the other hand, when the voltage exceeds 7.5 V, the brightness change during application of the adjustment pulse is too large and is easily recognized as flicker.

The application time of the adjustment pulse B can be appropriately selected within a range shorter than that of the write pulse. From the viewpoint of suppressing flickering of the screen, the change in L ^* (ΔL ^* when applying the adjustment pulse A and the adjustment pulse B ⁾ ) Is desirable to reduce. Specifically, when the absolute value of the applied voltage is 15 V, 1 ms to 100 ms is preferable, and 5 ms to 30 ms is more preferable. When the application time of the adjustment pulse B is less than 1 ms, the effect of returning the brightness by the adjustment pulse B is reduced, and when it exceeds 100 ms, it is difficult to maintain the DC balance including the adjustment pulse A. On the other hand, if the adjustment pulse B exceeds 100 ms, the flickering of the screen increases and it is easy to recognize as flicker.

By preventing the lightness L ^* during application of the adjustment pulse A and the adjustment pulse B from straddling the median value of lightness, flicker is hardly recognized. For example, when an electrophoretic element having a maximum value of L ^* of 70 and a minimum value of 20 is used, flicker is recognized by controlling L ^* so as not to cross the above-mentioned median value of 45. It becomes difficult. In order to achieve the above, it is also effective to prepare a plurality of adjustment pulses A and adjustment pulses B and apply them alternately. Further, it is more preferable that the change in the lightness L ^* during application of the adjustment pulse A and the adjustment pulse B is 15 or less, and it is further preferable that the change in the lightness L ^* is 10 or less. In order to be recognized as flickering, the amount of change in brightness and the rate of change are important. However, when the present invention is used, the rate of change can be controlled by the application voltage, application time, etc. of the adjustment pulse. The applied voltage of the adjustment pulse is preferably selected in consideration of both the change speed and the rewriting time. In addition, when the change in brightness is suppressed to 15 or less, the brightness does not change greatly, so that it is difficult for the observer to recognize the flicker. Furthermore, when the brightness change is suppressed to 10 or less, the brightness change is at a level that is hardly recognized, and the rewriting is more preferable.

(Examples 2, 3, 4, 5)
Subsequently, Examples 2, 3, 4, and 5 of the present invention will be described with reference to FIGS. 8 and 9A to 9D. FIG. 8 shows an example of 4-level gradation display. This is a case in which W (white), LG (light gray), DG (dark gray), and D (dark) are displayed in order of increasing brightness. The upper diagram of FIG. 8 shows the lightness in writing when the gradation is not changed from DG to DG in the second embodiment of the present invention. The lower diagram of FIG. 8 shows the waveform P21 of the second embodiment, which is adjusted using the adjustment pulse A, the adjustment pulse B, and the writing pulse so that the lightness L21 does not change from the original DG. 9A to 9D show the brightness and waveforms of Examples 3, 4, and 5 of the present invention. The brightness of Example 3 was L31, the waveform was P31, the brightness of Example 4 was L32, the waveform was P32, the brightness of Example 5 was L33, and the waveform was P33. In this case also, the writing is performed when the gradation is not changed from DG to DG. Display is once performed with the limit value of brightness in the writing pulse. After that, DG gradation is displayed. As described above, once the lightness limit value (D in the case of DG) on the side where the lightness change is small is displayed once, the lightness immediately before the desired gradation display settles to a constant value, so that the gradation display is more accurate. Can be performed. Specifically, as in L31, L32, and L33, even if L ^* before application of the write pulse is slightly shifted, subsequent gradation display is stabilized. Also, using the lightness limit value on the side where the lightness change is small does not straddle the median value of lightness, and thus flicker is difficult to be recognized. The above is the case of DG, but the case of LG and other gradations can also be implemented by appropriately changing the applied voltage and time.

(Example 6)
The sixth embodiment has the same waveform as that of the first embodiment except that the adjustment pulse A of the first embodiment is set to twice at 400 ms, the adjustment pulse B is set to one time, and the write pulse is set to 150 ms. Even when the waveform of the adjustment pulse A is repeated twice, it is possible to perform driving with little change in brightness and reduced flickering while maintaining DC balance.

(Example 7)
The seventh embodiment has the same waveform as that of the first embodiment, except that the adjustment pulse A of the first embodiment is once at 600 ms, the adjustment pulse B is not used, and the write pulse is 160 ms. Even when the waveform of the adjustment pulse A is only once, it is possible to perform driving with little change in brightness and reduced flickering while maintaining DC balance.

(Comparative Example 1)
Comparative Example 1 is a case where driving was not performed during partial rewriting. As shown in FIG. 4, if no driving is performed at the time of partial rewriting, the brightness of the rewritten portion will be different, and the observer will recognize it as an afterimage.

(Comparative Example 2)
Comparative Example 2 is an example in which 150 ms is written at −15 V and then 250 ms is written at +15 V. When writing at -15V, the display temporarily turns white, and then the desired black color is displayed. Since the screen blinks, it is recognized as flicker by the observer. In addition, since the DC balance is not achieved, the electrophoretic element is likely to deteriorate.

(Comparative Example 3)
Comparative Example 3 is an example in which after writing at −15 V for 100 ms, +15 V was written for 100 ms, −15 V at 100 ms, and +15 V at 250 ms. As in the comparative example 2, the screen blinks, so that it is recognized by the observer as flickering. In addition, since the DC balance is not achieved, the electrophoretic element is likely to deteriorate.

  Table 1 shows a list of driving waveforms of Examples 1 to 7 and Comparative Examples 1 to 3. As has been shown so far, by using the present invention, it is possible to drive in a state in which the DC balance is maintained, in which the time integration S of voltage (voltage × time because it is a rectangular wave) becomes plus or minus zero. It becomes possible. On the other hand, in Comparative Examples 1 to 3, the DC balance is not maintained, and the electrophoretic element is likely to deteriorate.

Also, L ^* change during driving operation was measured, and the value obtained by subtracting the minimum value from the maximum value is shown in Table 1 as the brightness change. In Examples 1, 2, 6, and 7, the brightness change is 15 or less, and writing with less flicker is realized. In Examples 3, 4, and 5, since the display is once performed with the limit value of brightness, the change in brightness is slightly large. However, the change in brightness in Comparative Examples 2 and 3 is 45 or more. Is greatly reduced. In Comparative Example 1, although there is almost no change in brightness, the brightness of black display is slightly increased with time. In Comparative Example 1, this portion has a brightness difference from other rewritten portions and is recognized as an afterimage.

  According to the present invention, since the adjustment pulse and the writing pulse are DC balanced, the electric field applied to the electrophoretic display panel is not biased, and long-term reliability can be maintained. In addition, since the electrophoretic display panel is driven by the adjustment pulse before the write pulse, the electrophoretic particles are loosened, and the variation in display characteristics after the write pulse is reduced. The polarity of the writing pulse in the present invention is a pulse when writing a desired image. For example, in the case of writing to white in black and white binary display, the brightness is in the direction of increasing. Since it is small, it is possible to minimize the change in brightness of the display image. In addition, since the display itself changes smoothly, there is little flickering on the screen and it is possible to reduce the viewer's discomfort.

  In addition, by using the adjustment pulse B having the same polarity as the write pulse and having a shorter time than the write pulse, the display changed by the adjustment pulse A can be returned to the vicinity of the original brightness. Further, by using the adjustment pulse A and the adjustment pulse B, it is possible to minimize the change in brightness, thereby reducing the flicker of the screen and reducing the discomfort of the observer.

  Further, by combining a plurality of adjustment pulses A and adjustment pulses B, the brightness of the display image can be adjusted more precisely, and the flicker suppression effect is improved.

Further, when the lightness L ^* when driven using the adjustment pulse and the writing pulse crosses the median value of the lightness of the display device, the observer will “change screen” or “flicker”. There is a risk of receiving. In this case, the median value of the brightness of the display device is an average value {(maximum value + minimum value) / 2} of the maximum value and the minimum value of the brightness of the display device. By using the adjustment pulse and the writing pulse so that the brightness does not straddle the median value of the brightness of the display device, it is possible to reduce the viewer's discomfort.

  Further, by suppressing the change in brightness to 15 or less using the adjustment pulse and the writing pulse, it is possible to reduce flickering on the display screen and to reduce the discomfort of the observer.

  Also, when performing gradation display, after loosening the particles with the adjustment pulse, once the display is performed with the limit value of brightness, the flow state of the electrophoretic particles becomes constant, and the brightness of the subsequent gradation display Variations are reduced. From the viewpoint of suppressing flickering on the screen, it is desirable to bring the limit value of brightness to the side where the amount of change from the current brightness is small.

  As described above, according to the display device and the driving method of the present invention, an electrophoretic display device capable of ensuring DC balance and performing high-contrast display while reducing afterimages and flickering of a display image, and an electric display A method for driving an electrophoretic display panel can be provided.

DESCRIPTION OF SYMBOLS 1 Electrophoretic display device 2 Display part 10 Controller (drive device of electrophoretic display device 1)
11 CPU
DESCRIPTION OF SYMBOLS 12 Memory 13 Communication apparatus 14 Flexible cable 20 Pixel 21 Pixel electrode 22 Counter electrode 23 Electrophoretic element 24 Pixel switching transistor 27 Retention capacity 28 TFT substrate 29 Counter substrate 30 Binder 31 Adhesive layer 40 Scan line 50 Data line 60 Scan line drive circuit 70 Data line driving circuit 80 Microcapsule (electrophoretic display material)
90 common potential line 100 common potential supply circuit L1 brightness profile 1
L21 Lightness profile 21
L31 Lightness profile 31
L32 Lightness profile 32
L33 Lightness profile 33
P1 Waveform profile 1
P21 Waveform profile 21
P31 Waveform profile 31
P32 Waveform profile 32
P33 Waveform profile 33
S1 Write pulse area S2 Adjustment pulse A area S3 Adjustment pulse B area t1 Write pulse time t2 Adjustment pulse A time t3 Adjustment pulse B time W1 Write pulse W2 Adjustment pulse A
W3 Adjustment pulse B
d1 L ^* decrease d2 L ^* increase

Claims (8)

A charged particle is enclosed between a pair of substrates each having an electrode on the opposite surface, and a display panel having a memory property for performing display by the movement of the charged particle, and display voltage is input to the display panel electrode to drive voltage A display device comprising:
The driving means applies a predetermined driving voltage pattern when displaying the same gradation as the previously displayed image,
The predetermined drive voltage pattern includes an adjustment pulse and a write pulse,
The adjustment pulse includes a first waveform having a polarity opposite to that of the write pulse and having an absolute voltage lower than that of the write pulse, whereby a change in brightness of the display device during application of the predetermined drive voltage pattern is predetermined. Is less than or equal to
The display device, wherein the adjustment pulse and the writing pulse are DC balanced.   The display device according to claim 1, wherein the adjustment pulse further includes a second waveform having the same polarity as the write pulse and a shorter application time than the write pulse.   The display device according to claim 2, wherein the adjustment pulse includes a plurality of the first waveform and the second waveform. The change in the brightness L ^* of the display device during application of the predetermined drive voltage pattern is the average value {(maximum value + minimum value) / 2} of the maximum value and the minimum value of the displayable brightness of the display device. The display device according to claim 1, wherein the display device does not straddle the median value of the brightness of the display device. The display according to any one of claims 1 to 4, wherein a brightness change value that is a value obtained by subtracting a minimum value from a maximum value of the brightness L ^* of the display device during application of the predetermined drive voltage pattern is 15 or less. apparatus.   6. The display device according to claim 1, wherein when the desired gray scale is displayed on the display device, the driving unit displays the desired gray scale once and then displays the desired gray scale. A charged particle is enclosed between a pair of substrates each having an electrode on the opposite surface, and a display panel having a memory property for performing display by the movement of the charged particle, and display voltage is input to the display panel electrode to drive voltage A display device comprising: a driving means for applying a display device, wherein the driving means executes the display device driving method,
When the driving means performs the display of the same gradation as the previously displayed image, a predetermined driving voltage pattern is applied,
The predetermined drive voltage pattern includes an adjustment pulse and a write pulse,
The adjustment pulse includes a first waveform having a polarity opposite to that of the write pulse and having a lower absolute value of the voltage than the write pulse, so that a change in brightness of the display device during the application of the predetermined drive voltage pattern is a predetermined value. And
The display device driving method, wherein the adjustment pulse and the writing pulse are in DC balance.   The display device driving method according to claim 7, wherein the adjustment pulse further includes a second waveform having the same polarity as the write pulse and a shorter application time than the write pulse.