JP5668771B2 - Control method for electrophoretic display device, control device for electrophoretic display device, electrophoretic display device, and electronic apparatus - Google Patents

Description

  The present invention relates to a driving method of an electrophoretic display device having a dispersion system containing electrophoretic particles, a driving circuit thereof, and an electronic apparatus using the driving circuit.

As a non-luminous display device, an electrophoretic display device using an electrophoretic phenomenon is known. The electrophoresis phenomenon is a phenomenon in which particles migrate due to Coulomb force when an electric field is applied to a dispersion system in which fine particles (electrophoretic particles) are dispersed in a liquid (dispersion medium).
The basic structure of the electrophoretic display device is such that one electrode and the other electrode face each other at a predetermined interval, and a dispersion system is enclosed between them. When a potential difference is applied between the two electrodes, the electrophoretic particles charged according to the direction of the electric field are attracted to one of the electrodes. Here, if the dispersion medium is dyed with a dye and the electrophoretic particles are composed of pigment particles, the observer can see the color of the electrophoretic particles or the color of the dye.

However, there is no conventional example of an active matrix type electrophoretic display device, and its driving method and driving circuit are not known.
The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a driving method and a driving circuit of an active matrix type electrophoretic display device.

In one aspect, the present invention provides a first electrode and a second electrode, a dispersion system containing electrophoretic particles disposed between the first electrode and the second electrode, and a plurality of dispersion systems. Scan lines, a plurality of data lines intersecting with the plurality of scan lines, and the data lines, the scan lines, and the first electrodes. And a switching element electrically connected to the electrophoretic display device, wherein the first voltage is applied between the first electrode and the second electrode when switching the display. And applying a second voltage having a polarity opposite to that of the first electrode between the first electrode and the second electrode after the first step. a second step, after the second step, the same conductive with the second electrode to the first electrode Anda third step of applying, the application time of the second voltage in the second step is shorter than the application time of the first voltage at the first step, the electrophoretic display device A driving method is provided.
In another aspect, the present invention provides a first electrode and a second electrode, a dispersion system containing electrophoretic particles disposed between the first electrode and the second electrode, and a plurality of dispersion systems. Scan lines, a plurality of data lines intersecting with the plurality of scan lines, and the data lines, the scan lines, and the first electrodes. An electrophoretic display device having a switching element electrically connected to the first electrode, and a first voltage between the first electrode and the second electrode when switching the display. And applying a second voltage having a polarity opposite to that of the first electrode between the first electrode and the second electrode after the first step. a second step, after the second step, the same conductive with the second electrode to the first electrode Controlling the electrophoretic display device so as to execute a third step of applying, to the said application time of the second voltage at the second step, the first voltage in the first step Provided is a control device for an electrophoretic display device that is shorter than an application time.
In another aspect, the present invention provides a first electrode and a second electrode, a dispersion system containing electrophoretic particles disposed between the first electrode and the second electrode, and a plurality of dispersion systems. Scan lines, a plurality of data lines intersecting with the plurality of scan lines, and the data lines, the scan lines, and the first electrodes. An electrophoretic display device having a switching element electrically connected to the first electrode and the second electrode between the first electrode and the second electrode when switching display. A voltage is applied, and in a second step after the first step, a second voltage having a polarity opposite to that of the first electrode is provided between the first electrode and the second electrode. is applied in a third step following said second step, said first electrode The same voltage as the second electrode is applied, the application time of the second voltage in the second step is shorter than the application time of the first voltage at the first step, an electrophoretic display device provide.

According to the present invention, since a constant voltage is applied between the electrodes for a period corresponding to the display gradation, the spatial state can be changed by applying the Coulomb force to the electrophoretic particles.
Thereafter, in order to stop the movement of the electrophoretic particles, each electrode is made equipotential. Since the electric charge accumulated in the capacitor composed of both electrodes and the dispersion system can be discharged, the generation of the electric field can be completely stopped and the spatial state of the electrophoretic particles can be fixed. In order to perform gradation display, it is preferable to vary the particle characteristics of the dispersed electrophoretic particles.

  Further, when the display screen is switched, it is preferable that the application time of the constant voltage is a time corresponding to the difference between the display gradation after switching and the display gradation before switching. By doing so, an electric field is applied to the dispersion system for a time corresponding to the difference gray level, so that the electrophoretic particles change their spatial state on the basis of the current state. That is, instead of initializing the spatial state of the electrophoretic particles and displaying the next gradation, the spatial state is continuously changed. Therefore, the initialization process can be omitted, and the display gradation can be changed at high speed.

  In addition, when a voltage for braking the movement of the electrophoretic particles is applied between both electrodes, a voltage that attenuates the movement of the electrophoretic particles is applied between the electrodes, and then the potential of each electrode is set to be equal. It is desirable to make it a potential. For example, when the viscosity resistance of the dispersion medium is small, even if the potential of both electrodes is made equal and the generation of the electric field is stopped, the electrophoretic particles continue to move due to inertia and the brightness of the display image changes. become. According to the present invention, since the voltage that attenuates the movement is supplied, the electrophoretic particles can be stopped in a short time. Since the moving direction of the electrophoretic particles is determined by the direction of the voltage to be applied first, it is preferable that the voltage for braking has the opposite polarity.

In a preferred aspect, in the driving method, an elapsed time from the end of the application time is measured, and when the measured time exceeds a predetermined reference time, the constant voltage is again applied for the same application time. The method further includes applying between the first electrode and the second electrode.
Electrophoretic particles may settle and float due to the weight, but according to the present invention, a constant voltage is written again when the reference time is exceeded, so that the same image quality as the first is maintained even if left for a long time. be able to.

  In a preferred aspect, the driving method of the present invention includes a plurality of data lines, a plurality of scanning lines that intersect the plurality of data lines, a common electrode, and the plurality of data lines and the plurality of data as elements of each pixel. A plurality of pixel electrodes provided corresponding to each intersection with the scanning line and facing the common electrode across a certain gap, and the plurality of pixel electrodes and the common electrode as other elements of the pixel Between the plurality of dispersion systems each containing the electrophoretic particles and the intersections of the plurality of data lines and the plurality of scanning lines, and pass through the intersections. A plurality of switching elements for connecting each of the on / off switching control terminals to the scanning line and connecting a data line passing through the intersection when the scanning line is in an on state to a pixel electrode provided corresponding to the intersection; Electrophoresis with A driving method of the display device, wherein the electrophoretic particles are moved to a position corresponding to the display gradation of the pixel between each of the plurality of pixel electrodes and the common electrode using a constant voltage based on image data. A determination step for determining an application time required to cause the power supply, a step of supplying a predetermined common electrode voltage to the common electrode, a scan line is sequentially selected, and the scan line is selected with respect to the selected scan line. A voltage for turning on all the connected switching elements at once is applied for a certain period, and each of the plurality of data lines corresponds to an intersection of the data line and the selected scanning line. Applying the constant voltage to the pixel electrode of the pixel for the application time determined in the determining step, and then applying the common electrode voltage. That.

  According to the present invention, since a constant voltage can be written for a period corresponding to the gradation to be displayed on each pixel electrode, an image can be displayed in a matrix. In addition, by writing the common electrode voltage to the pixel electrode, the charge accumulated in the pixel capacitor is discharged, so that an electric field between the electrodes is not generated even when the switching element is turned off. Therefore, the spatial state of the electrophoretic particles can be fixed, and a display image can be held.

In a preferred aspect, the driving method of the present invention includes a plurality of data lines, a plurality of scanning lines that intersect the plurality of data lines, a common electrode, and the plurality of data lines and the plurality of data as elements of each pixel. A plurality of pixel electrodes provided corresponding to each intersection with the scanning line and facing the common electrode across a certain gap, and the plurality of pixel electrodes and the common electrode as other elements of the pixel Between the plurality of dispersion systems each containing the electrophoretic particles and the intersections of the plurality of data lines and the plurality of scanning lines, and pass through the intersections. A plurality of switching elements for connecting each of the on / off switching control terminals to the scanning line and connecting a data line passing through the intersection when the scanning line is in an on state to a pixel electrode provided corresponding to the intersection; Electrophoresis with A method for driving the display device, comprising: supplying a predetermined common electrode voltage to the common electrode; and using a constant voltage based on image data between each of the plurality of pixel electrodes and the common electrode. A determination step for determining an application time required to move the electrophoretic particles to a position corresponding to the display gradation of the pixel, and the plurality of scanning lines based on the application time determined in the determination step. In the first period of the horizontal scanning period according to the timing determination step for determining the timing to be selected, the voltage to be supplied to the plurality of data lines and the application timing of the voltage, and the timing determined in the timing determination step, A plurality of scanning lines are sequentially selected, and all the switching elements connected to the scanning line are selected for the selected scanning line. A scanning line corresponding to the pixel is applied in accordance with the timing determined in the timing determination step and the step of applying the selection voltage for collectively turning on and applying the constant voltage to each of the plurality of data lines Is selected in the second period of the horizontal scanning period, and the selection voltage is applied to the scanning line, and the braking voltage for braking the movement of the electrophoretic particles is applied only to the data line corresponding to the pixel. And selecting a scanning line corresponding to the pixel in a third period in a horizontal scanning period according to the timing determined in the timing determining step, applying the selection voltage to the scanning line, and Applying a common electrode voltage only to a data line corresponding to the pixel.
According to the present invention, for example, a constant voltage and a braking voltage can be held in units of horizontal scanning periods. As a result, not only the constant voltage but also the braking voltage can be set low.

  In another aspect, the present invention provides a plurality of data lines, a plurality of scan lines that intersect the plurality of data lines, a common electrode, and the plurality of data lines and the plurality of scans as one element of each pixel. A plurality of pixel electrodes provided corresponding to each intersection with the line and opposed to the common electrode with a certain gap therebetween, and the plurality of pixel electrodes and the common electrode as other elements of the pixel. A plurality of dispersion systems each sandwiched between and each containing electrophoretic particles, and a scanning line provided corresponding to each intersection of the plurality of data lines and the plurality of scanning lines and passing through the intersection And a plurality of switching elements for connecting data lines passing through the intersections to pixel electrodes provided corresponding to the intersections when the ON / OFF switching control terminals are connected to each other. Driving an electrophoretic display Necessary for moving the electrophoretic particles to a position corresponding to the display gradation of the pixel between each of the plurality of pixel electrodes and the common electrode using a constant voltage based on image data A timing generator for determining an appropriate application time, an application unit for applying a predetermined common electrode voltage to the common electrode, and the scanning line are sequentially selected, and the selected scanning line is connected to the scanning line. A scanning line driving unit that applies a selection voltage that turns on all the switching elements at once, and a timing generator that determines a pixel electrode of each pixel corresponding to the scanning line in a certain scanning line selection period A data line driving unit that applies the common electrode voltage to each of the data lines after applying the constant voltage to each of the plurality of data lines for a given application time; To provide a driving circuit of the electrophoretic display device characterized by comprising.

  In addition, an electronic apparatus according to the present invention includes the above-described electrophoretic display device as a display unit. For example, an electronic book, a personal computer, a mobile phone, an electronic advertising bulletin board, an electronic road sign, etc. Corresponds to this.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<1: First Embodiment>
The electrophoretic display device according to the first embodiment displays an image corresponding to an input image signal VID. This device can display either still images or moving images, but is particularly suitable for displaying still images.

<1-1: Overall Configuration of Electrophoretic Display Device>
The electrophoretic display device of this embodiment includes an electrophoretic display panel and a peripheral circuit. First, the mechanical configuration of the electrophoretic display panel will be described. FIG. 1 is an exploded perspective view showing a mechanical configuration of an electrophoretic display panel according to an embodiment of the present invention. FIG. 2 is a partial cross-sectional view of the electrophoretic display panel.

  As shown in FIGS. 1 and 2, the electrophoretic display panel A includes an element substrate 100 and a counter substrate 200. The element substrate 100 is made of glass, semiconductor, or the like. Pixel electrodes 104 and partition walls 110 are formed on the element substrate 100. A common electrode 201 is formed on the counter substrate 200.

  The electrophoretic display panel A is obtained by bonding the element substrate 100 and the counter substrate 200 so that the electrode formation surfaces face each other. The dispersion system 1 is sealed in the gap between the element substrate 100 and the counter substrate 200. The height of the partition 110 is constant. Therefore, the distance between the element substrate 100 and the counter substrate 200 is constant. The counter substrate 200, the common electrode 201, and the sealing material 202 are transparent. The observer views the image from the direction of the arrow shown in FIG.

  Further, the dispersion system 1 is obtained by dispersing the electrophoretic particles 3 in the dispersion medium 2. An additive such as a surfactant may be added to the dispersion medium 2 as necessary. In order to avoid sedimentation of the electrophoretic particles 3 due to gravity, it is desirable that the specific gravity of the dispersion medium 2 and the electrophoretic particles 3 is substantially equal.

  The partition 110 separates pixels that are display units of an image. The space partitioned by the partition 110 is called a divided cell 11C. The divided cell 11C is filled with the dispersion system 1. The partition 110 restricts the region in which the electrophoretic particles 3 can migrate to the inside of one divided cell 11C. In the dispersion system 1, the position of the electrophoretic particles 3 may be biased. In the dispersion system 1, condensation may occur. Aggregation refers to a phenomenon in which a plurality of particles are combined into a large mass. The partition 110 prevents the electrophoretic particles 3 from being biased or condensed. As a result, the quality of the display image is improved.

The dispersion medium 2 in this example is black. The electrophoretic particles 3 are white particles such as titanium oxide. The electrophoretic particles 3 are charged with a positive charge.
Of course, the electrophoretic display panel A can be adapted to full color display. In such a case, each pixel displays one of the primary colors (RGB). For this reason, as the dispersion system 1, three types corresponding to the R color, the G color, and the B color are used.
The dispersion system 1r corresponding to the R color includes red electrophoretic particles 3r and a cyan dispersion medium 2r. For example, iron oxide can be used as the electrophoretic particles 3r. The dispersion system 1g corresponding to G color includes green electrophoretic particles 3g and magenta dispersion medium 2g. For example, cobalt green pigment particles can be used as the electrophoretic particles 3g. The dispersion system 1b corresponding to the B color includes blue electrophoretic particles 3b and a yellow dispersion medium 2b. For example, cobalt blue pigment particles can be used as the electrophoretic particles 2b.

  In other words, the electrophoretic particles 3 corresponding to the display color are used, while the dispersion medium 2 is a color that absorbs the display color (complementary color in the above example). If the electrophoretic particles 3 are floating near the electrode on the display surface side, the electrophoretic particles 3 reflect light having a wavelength corresponding to the display color. The observer recognizes the color by this reflected light. On the other hand, if the electrophoretic particles 3 have settled in the vicinity of the electrode on the side opposite to the display surface, light having a wavelength corresponding to the display color is absorbed by the dispersion medium 2. Then, since light having a wavelength corresponding to the display color does not reach the observer, the observer cannot recognize the color.

  The intensity of light reaching the observer is determined by how much the dispersion medium 2 absorbs the light reflected by the electrophoretic particles 3. The electric field strength applied to the dispersion system 1 determines how the electrophoretic particles 3 are distributed in the thickness direction of the dispersion system 1. Therefore, in order to display a desired gradation on the electrophoretic display panel A, the following two elements are necessary. The first element is to use in combination with the electrophoretic particles 3 and the dispersion medium 2 that absorbs the light reflected by the electrophoretic particles 3. The second factor is to control the electric field strength.

  Next, in the element substrate 100, a region where the partition 110 is formed is a display region A1. In addition to the pixel electrode 104, a scanning line, a data line, and a thin film transistor (hereinafter referred to as TFT) are formed there. The TFT functions as a switching element. In the peripheral region A2, a scanning line driving circuit, a data line driving circuit, and external connection electrodes, which will be described later, are formed.

  Next, the electrical configuration of the electrophoretic display device will be described with reference to FIG. FIG. 3 is a block diagram showing an electrical configuration of the electrophoretic display device. As shown in this figure, the electrophoretic display device includes an electrophoretic display panel A, an image signal processing circuit 300A, and a timing generator 400A. Here, the image signal processing circuit 300A performs correction processing on the input image signal VID to generate image data D. The correction processing is in accordance with the electrical characteristics of the electrophoretic display panel A. In the case of color display, the image data D may be composed of three types of data corresponding to RGB colors.

  The timing generator 400A generates various timing signals in synchronization with the image data D. The timing signal is used to control the scanning line driving circuit 130A and the data line driving circuit 140A.

  In the display area A1 of the electrophoretic display panel A, a plurality of scanning lines 101 are formed in parallel with the X direction. The Y direction is orthogonal to the X direction. In the display area A1, a plurality of data lines 102 are formed in parallel with the Y direction. A TFT 103 is disposed in the vicinity of each intersection between the scanning line 101 and the data line 102.

  The gate electrode of the TFT 103 is connected to the scanning line 101. The source electrode of the TFT 103 is connected to the data line 102. The drain electrode of the TFT 103 is connected to the pixel electrode 104. Each pixel includes a pixel electrode 104, a common electrode 201 formed on the counter substrate 102, and a dispersion system 1 sandwiched between the two electrodes. Thus, the pixels are arranged in a matrix corresponding to the intersection of the scanning line 101 and the data line 102. Note that the scanning line driving circuit 130A and the data line driving circuit 140A are configured using TFTs. The scanning line driving circuit 130A and the data line driving circuit 140A are formed by a manufacturing process common to the TFT 103 of the pixel. As a result, the electrophoretic display panel A can be integrated and the manufacturing cost can be reduced.

  In such an electrophoretic display panel A, when a certain scanning line signal Yj becomes active, the TFT 103 connected to the jth scanning line 101 is turned on. At this time, data line signals X 1, X 2,..., Xn are supplied to the pixel electrode 104. On the other hand, a common electrode voltage Vcom is supplied to the common electrode 201 of the counter substrate 200 from a power supply circuit (power supply unit) (not shown). As a result, an electric field is generated between the pixel electrode 104 and the common electrode 201. Then, the electrophoretic particles 3 of the dispersion system 1 migrate, and gradation display according to the value of the image data D is performed for each pixel.

<1-2: Display principle>
Next, the principle of gradation display will be described. FIG. 4 is a cross-sectional view showing a simplified structure of the divided cell. In the electrophoretic display device of this example, first, the electrophoretic particles 3 are attracted toward the pixel electrode 104 as shown on the left side of FIG. If the positively charged electrophoretic particles 3 are used, a negative voltage is supplied to the pixel electrode 104 for a predetermined time with reference to the voltage of the common electrode 201. In the following description, the operation for attracting the electrophoretic particles 3 to one electrode in this way is referred to as a reset operation.

  Next, a positive voltage is applied to the pixel electrode 104 as shown on the right side of FIG. Then, the electrophoretic particles 3 move to the common electrode 201 side by Coulomb force. On the other hand, when the voltage application is stopped, the Coulomb force does not act, so the electrophoretic particles 3 are stopped by the viscous resistance of the dispersion medium 2. The moving speed of the electrophoretic particles 3 is determined according to the electric field strength, that is, the applied voltage. Therefore, the moving distance of the electrophoretic particles 3 is determined according to the applied voltage and the applied time. If the applied voltage is made constant, the position of the electrophoretic particles 3 can be controlled in the thickness direction by adjusting the application time.

Light incident from the common electrode 201 is reflected by the electrophoretic particles 3, and this reflected light passes through the common electrode 201 and reaches the eyes of the observer. Incident light and reflected light are absorbed by the dispersion medium 2, and the degree of absorption is proportional to the optical path length. Therefore, the gradation recognized by the observer is determined by the position of the electrophoretic particle 3. As described above, when the applied voltage is made constant, the position in the thickness direction of the electrophoretic particles 3 is determined according to the application time. Therefore, if the constant voltage is applied only for the time corresponding to the gradation to be displayed, it is desired. Gradation display can be obtained.

  By the way, the dispersion system 1 includes a large number of electrophoretic particles 3. Here, if particle characteristics such as electrical characteristics (for example, charge amount) and mechanical characteristics (for example, particle diameter, weight) are all the same, all particles have the same speed. Move with. That is, all the electrophoretic particles 3 behave in the same way.

  The thickness of the divided cell 11c is several μm to several tens of μm, and the maximum moving distance is extremely short. For this reason, in order to increase the number of gradations, it is necessary to control a minute movement distance. Then, the application time for one gradation becomes extremely short, and gradation control becomes difficult.

  Therefore, the electrophoretic particles 3 of the present embodiment have variations in particle characteristics. If the particle characteristics vary, the position of the electrophoretic particles 3 has a widening when a certain voltage is applied for a certain period of time. FIG. 5 is a graph showing an example of the relationship between voltage application time and gradation density. This graph is obtained by simulation under the following conditions. The first condition is that when the voltage of 5 V is applied, the average time for the electrophoretic particles 3 to reach the common electrode 201 is 50 msec. The second condition is that the standard deviation of the applied voltage required to reach is 2 msec.

In FIG. 5, the solid line indicates the gradation characteristics with respect to the application time, and the dotted line indicates the probability density with respect to the application time. Here, the probability density is obtained by normalizing the number of electrophoretic particles 3 reaching the common electrode 201 with an average value of 50 msec.
As shown in this figure, when the application time is 45 msec or less, the electrophoretic particles 3 hardly reach the common electrode 201. When the application time is 50 msec, half of the electrophoretic particles 3 reach the common electrode 201. Further, when the application time is 55 msec or more, most of the electrophoretic particles 3 reach the common electrode 201. Therefore, if the application time is controlled between 45 msec and 55 mesc according to the gradation to be displayed, a desired gradation display can be performed.

<1-3: Drive circuit>
Next, a driving circuit for driving each scanning line 101 and each data line 102 will be described. First, the scan line driver circuit 130A illustrated in FIG. 3 includes a shift register. The scanning line driving circuit 130A sequentially shifts the Y transfer start pulse DY based on the Y clock signal YCK and the inverted Y clock YCKB to generate the scanning line signals Y1, Y2,. The Y transfer start pulse DY becomes active for a certain period from the start of the vertical scanning period. The timing generator 400A supplies the Y clock signal YCK, the inverted Y clock YCKB, and the Y transfer start pulse DY to the scanning line driving circuit 130A. Thereby, the active period (H level period) of the scanning line signals Y1, Y2,..., Ym is sequentially shifted as shown in FIG.

  Next, the data line driving circuit 140A will be described. FIG. 6 is a block diagram of the data line driving circuit 140A. FIG. 7 is a timing chart of the data line driving circuit 140A. As shown in FIG. 6, the data line driving circuit 140A includes an X shift register 141, a bus BUS, switches SW1 to SWn, a first latch 142, a second latch 143, and a PWM circuit 145. 6-bit image data D is externally supplied to the bus BUS.

First, the X shift register 141 sequentially shifts the X transfer start pulse DX according to the X clock XCK and the inverted X clock XCKB. Thereby, sampling pulses SR1, SR2,..., SRn shown in FIG. 7 are generated.
Next, the first latch 142 includes a plurality of latch circuits. The bus BUS is connected to each latch circuit of the first latch group 142 via the switches SW1 to SWn. Sampling pulses SR1, SR2,..., SRn are supplied to the control input terminals of the switches SW1 to SWn. Therefore, the image data D is taken into the first latch 142 in synchronization with the sampling pulses SR1, SR2,. Each switch SW1 to SWn shown in FIG. 6 is actually composed of a set of six switch circuits. This is because it corresponds to 6-bit image data D.

  Next, the first latch 142 latches the image data D supplied from the switches SW1 to SWn. Thereby, dot sequential image data Da1 to Dan are obtained (see FIG. 7). The second latch 143 latches the dot sequential image data Da1 to Dan with a latch pulse LAT. Here, the latch pulse LAT is a signal that becomes active every horizontal scanning period as shown in FIG. Therefore, the second latch 143 generates line-sequential image data Db1 to Dbn by aligning the phases of the dot-sequential image data Da1 to Dan for each horizontal scanning period.

  FIG. 8 is a block diagram showing a configuration of the PWM circuit 145. As shown in this figure, the PWM circuit 145 includes n unit circuits R1 to Rn and a counter 144. Each unit circuit R1 to Rn includes a comparator 1451, an SR latch 1452, and a selection circuit 1453.

  The counter 144 counts the clock signal CK from the beginning of the horizontal scanning period, and generates count data CNT indicating the count result. The comparator 1451 compares the line-sequential image data Db1 to Dbn and the count data CNT to generate a comparison signal CS. The comparison signal CS is at the H level when the line-sequential image data Db1 to Dbn and the count data CNT coincide with each other, and at the L level when they do not coincide with each other. The comparison signal CS is supplied to the reset terminal of the SR latch 1452. The set signal SET is supplied from the timing generator 400C to the set terminal of the SR latch 1452. The set signal SET becomes H level for a predetermined period from the beginning of the horizontal scanning period.

  The SR latch 1452 of each unit circuit R1 to Rn generates PWM signals (pulse width modulation signals) W1 to Wn. The PWM signals W1 to Wn become H level when the set signal SET becomes H level, and then become L level when the comparison signal CS becomes H level.

  FIG. 9 is a timing chart showing line-sequential image data values and PWM signal waveforms. As shown in this figure, the active (H level) period of each PWM signal is a period corresponding to the gradation value indicated by line-sequential image data. However, even when the gradation value is “111111” (100%), the frequency of the clock signal CK is selected so that the ratio of the active period of the PWM signal to one horizontal scanning period is about 2/3. ing.

  Next, each selection circuit 1453 selects and outputs a predetermined voltage from the common electrode voltage Vcom, the applied voltage Va, and the reset voltage Vrest based on the PWM signals W1 to Wn and the reset timing signal Cr. The selection conditions are as follows. First, the selection circuit 1453 selects the reset voltage Vrest when the reset timing signal Cr is active (H level). Second, the selection circuit 1453 selects the applied voltage Va when the reset timing signal Cr is inactive (L level) and the PWM signal is active (H level). Third, the selection circuit 1453 selects the common electrode voltage Vcom when the reset timing signal Cr is inactive (L level) and the PWM signal is inactive (L level).

  Here, the operation of the j-th unit circuit Rj will be specifically described with reference to the timing chart shown in FIG. In this example, it is assumed that the reset timing signal Cr is inactive during a certain horizontal scanning period, and the gradation value indicated by the line-sequential image data Dbj is “32”.

  As shown in this figure, from the start time Tss of the horizontal scanning period, the count data CNT starts increasing and the set signal SET becomes active. The PWM signal Wj becomes H level in synchronization with the set signal. When the time Te is reached, the value of the count data CNT becomes “32”, and the comparison signal CS becomes active. Then, the PWM signal Wj changes from the H level to the L level. As a result, during the period from time Tss to time Te, the PWM signal Wj becomes H level.

  As described above, the selection circuit 1453 selects the applied voltage Va during the period when the PWM signal Wj is at the H level, and selects the common electrode voltage Vcom during the L level period. Therefore, as shown in FIG. 10, the data line signal Xj becomes the applied voltage Va in the period from the time Ts to the time Te, and becomes the common electrode voltage Vcom from the time Te to the end of the horizontal scanning period.

  That is, the data line signal Xj becomes a constant voltage only during a period corresponding to the gradation to be displayed, and becomes the common electrode voltage Vcom during other periods. In this way, the data line driving circuit 140 </ b> A generates the data line signals X <b> 1 to Xn and supplies them to the data lines 102.

<1-4: Operation of Electrophoretic Display Device>
Next, the operation of the electrophoretic display device will be described.

<1-4-1: Overall operation>
FIG. 11 is a timing chart showing the overall operation of the electrophoretic display device. The outline of the operation will be described with reference to this figure. First, when the power supply of the electrophoretic display device is switched from the off state to the on state at time t0, the power is supplied to the image signal processing circuit 300A, the timing generator 400A, and the electrophoretic display panel A.

  The timing generator 400A activates the reset timing signal Cr for one field period at time t1 when the predetermined period has elapsed and the circuit operation is stable. In the reset period Tr, as described in the display principle, the electrophoretic particles 3 are attracted to the pixel electrode 104 side. As a result, the spatial state of the electrophoretic particles 3 is initialized.

  Each selection circuit 1453 of the data line driving circuit 140A selects the reset voltage Vrest during this period, and outputs this to the data lines 102 as data line signals X1 to Xn. Then, the scanning line driving circuit 130A sequentially selects each scanning line 101, whereby the reset voltage Vrest is written to all the pixel electrodes 104.

  Next, when the time t2 is reached, the writing period Tw starts. In the writing period Tw, the image signal processing circuit 300A outputs the image data D over one field period. The applied voltage Va is written to each pixel electrode 104 only for a period corresponding to the gradation to be displayed, and one display screen is completed.

  Next, the holding period Th from time t3 to time t4 is a period for holding the image written in the immediately preceding writing period Tw. The length of the holding period Th can be arbitrarily set. In this period, the image signal processing circuit 300A stops operating. An electric field is not generated between the pixel electrode 104 and the common electrode 201. Since the electrophoretic particles 3 migrate due to Coulomb force, there is no change in the spatial state if there is no electric field. Therefore, a still image is displayed during the period.

  Next, a period from time t4 to time t6 is a rewriting period Tc for rewriting an image. In the rewrite period Tc, the reset operation and the write operation are performed as in the period from time t1 to time t3. Thereby, the display screen can be updated.

<1-4-2: Reset operation>
Next, the reset operation will be described in detail. FIG. 12 is a timing chart of the electrophoretic display device in the reset operation. In the following description, a pixel in i row and j column is represented as Pij, and a voltage applied to the pixel electrode 104 of the pixel Pij is represented as Vij. As described above, in the reset period Tr, the reset timing signal Cr becomes active (H level) as shown in FIG. 12, so the voltages of the data line signals X1 to Xn become the reset voltage Vrest.

  In this example, since the electrophoretic particles 3 are positively charged, the reset voltage Vrest takes a negative value with the common electrode voltage Vcom as the center. Here, when the scanning line signal Y1 becomes active (H level), the TFT 103 in the first row is turned on, and the reset voltage Vrest is written to each pixel electrode 104. Thereafter, the reset voltage Vrest is written to each pixel electrode 104 in the second row, the third row,..., The m-th row. For example, when the scanning line signal Y1 changes from active to inactive at time tx, each TFT 103 in the first row is turned off, and the pixel electrode 104 and the data line 102 are disconnected. However, even when the TFT 103 is turned off, the reset voltage Vrest is maintained in the pixel electrode 104 in the first row. This is because each pixel has a pixel capacitance constituted by the pixel electrode 104, the dispersion system 1, the common electrode 201, and the like, and charges corresponding to the reset voltage Vrest are accumulated in the pixel capacitance.

  When the reset voltage Vrest is thus applied to the pixel electrode 104, the electrophoretic particles 3 in the dispersion system 1 are attracted to the pixel electrode 104, and the spatial state thereof is initialized.

<1-4-3: Write operation>
Next, the write operation will be described in detail. FIG. 13 is a timing chart of the electrophoretic display device in the writing operation. Here, the writing operation in the pixels of i rows (i th scanning line) and j columns (j th data line) will be described. Of course, similar writing is performed in other pixels. In the following description, the luminance of the pixel Pij is expressed as Iij.

  As shown in FIG. 12, the data line signal Xj supplied to the jth data line 102 becomes the applied voltage Va in the voltage application period Tv that is the active period of the PWM signal Wj. On the other hand, the PWM signal Wj becomes the common electrode voltage Vcom in the non-bias period Tb that is the inactive period of the PWM signal Wj. The waveform of the data line signal Xj indicated by the solid line is when the gradation to be displayed is 100%, and the waveform of the data line signal Xj indicated by the alternate long and short dash line is when the gradation to be displayed is 50%.

  Further, the scanning line signal Yi supplied to the i-th scanning line 101 becomes active during the i-th horizontal scanning period. Therefore, the TFT 103 of the pixel Pij is turned on during the horizontal scanning period, and the data line signal Xj from time T1 to time T3 is taken into the pixel electrode 104 of the pixel Pij. That is, in this example, the operation from writing the applied voltage Va to the pixel electrode 104 to writing the common electrode voltage Vcom is completed in a certain selection period of a certain scanning line.

  Next, the behavior of the electrophoretic particles 3 in the pixel Pij will be considered. Since the above-described reset operation is performed before this writing operation, the electrophoretic particles 3 of the pixels Pij are all located on the pixel electrode 104 side at time T1. At this time, when the applied voltage Va is applied to the pixel electrode 104, an electric field is applied from the pixel electrode 104 toward the common electrode 201. Therefore, the electrophoretic particles 3 start to move from time T1.

  Since the electrophoretic particles 3 in this example are white and the dispersion medium 2 is black, the luminance Iij of the pixel Pij increases as the electrophoretic particles 3 approach the common electrode 201. Therefore, as shown in FIG. 13, the luminance Iij gradually increases from time T1.

  Incidentally, the pixel Pij is configured by sandwiching the dispersion system 1 between the pixel electrode 104 and the common electrode 201. For this reason, the pixel Pij equivalently includes a pixel capacitance having a capacitance value corresponding to the electrode area, the distance between the electrodes, and the dielectric constant of the dispersion system 1. Therefore, even if the power supply to the pixel electrode 104 is stopped by turning off the TFT 103, charges are accumulated in the pixel capacitor. Therefore, a constant electric field is continuously generated between both electrodes. Since the electrophoretic particles 3 continue to migrate toward the common electrode 201 as long as an electric field is applied, a period in which the generation of the electric field is stopped, in other words, a step of removing charges accumulated in the pixel capacitor is necessary. The no-bias period Tb is provided for this purpose.

  In the no-bias period Tb, the common electrode voltage Vcom is applied to the pixel electrode 104, so that the voltages of the pixel electrode 104 and the common electrode 201 match at time T2. For this reason, the Coulomb force does not act on the electrophoretic particles 3 from time T2. Here, if the viscosity resistance of the dispersion medium 2 is large to some extent, the electrophoretic particles 3 stop the migration at time T2 when the external force stops working. As a result, the luminance Iij takes a constant value from time T2 as shown in FIG. When the viscosity resistance of the dispersion medium 2 is small, the electrophoretic particles 3 are stopped after the electrophoretic particles 3 migrate due to inertia even if the Coulomb force stops working. In such a case, the image signal D may be generated in the image signal processing circuit 300 </ b> A so as to correct for the migration due to inertia.

  In this writing operation, first, the application voltage Va is applied to the pixel electrode 104 of the pixel Pij for a voltage application period Tv corresponding to the gradation. Then, the electrophoretic particles 3 move by a distance corresponding to the gradation to be displayed. Next, the common electrode voltage Vcom is written to the pixel electrode 104 to stop the migration of the electrophoretic particles 3. By these two steps, the luminance Iij of the pixel Pij can be made to correspond to the gradation to be displayed.

  In this example, the common electrode voltage Vcom is written to stop the electrophoresis of the electrophoretic particles 3. However, it is not necessary to write a voltage that completely matches the common electrode voltage Vcom, and any voltage that can stop the migration of the electrophoretic particles 3 may be used. Since the electrophoretic particles 3 cannot migrate unless the viscous resistance is overcome, when the viscous resistance of the dispersion medium 2 is large, the voltage of the non-bias period Tb may be slightly different from the common electrode voltage Vcom.

<1-4-4: Holding operation>
Next, the holding operation will be described. In FIG. 13, when the time T3 is reached, the scanning line signal Yi transitions from active to inactive, so that the TFT 103 of the pixel Pij is turned off. As described above, since the common electrode voltage Vcom is applied to the pixel electrode 104 in the non-bias period Tb, no electric field is generated.

  Therefore, unless a new voltage is written to the pixel electrode 104, no electric field is applied to the dispersion system 1. As a result, the spatial state of the electrophoretic particles 3 in the dispersion system 1 is maintained. That is, the content of the display image can be held.

  In the holding period Th, since it is not necessary to write a voltage to the pixel electrode 104, it is not necessary to generate the scanning line signals Y1 to Ym and it is not necessary to generate the data line signals X1 to Xn. For this reason, in the said period, power consumption can be reduced with the various methods described below.

  The first method is to turn off the main power supply of the electrophoretic display device itself. Thus, the operation of the electrophoretic display panel A, the image signal processing circuit 300A and the timing generator 400A as peripheral circuits is stopped, and no power is consumed.

  The second method is to stop the power supply to the electrophoretic display panel A. Thereby, the power consumed by the electrophoretic display panel A can be reduced.

The third method is to stop supplying the Y clock YCK and the inverted Y clock YCKB, the X clock XCK, the inverted X clock XCKB, and the clock signal CK to the scanning line driving circuit 130A and the data line driving circuit 140A. It is.
As described above, since the scanning line driving circuit 130A and the data line driving circuit 140A are composed of complementary TFTs, power is consumed only when current flows, in other words, only when there is a logic level inversion. . Therefore, power consumption can be reduced by stopping the supply of the clock.

<1-4-5: Rewriting operation>
Next, a rewriting operation for rewriting the contents of the display screen will be described. In the rewriting operation, there are various modes described below.
First, in the first aspect, the reset operation described above is performed to sequentially initialize each row, and then the write operation described above is performed to sequentially perform pulse width modulated data line signals X1 to X1. Xn is written into the pixel electrode 104. As a result, the entire screen can be rewritten.

  Next, in the second mode, the reset operation and the write operation are performed only on the lines that need to be rewritten. Here, a case where the jth and j + 1th lines are rewritten will be described as an example. FIG. 14 is a timing chart for explaining the reset operation according to the second embodiment.

  First, in the reset period Tr, the image signal processing circuit 300A outputs data indicating the common electrode voltage Vcom as the image data D. That is, the value of the image data D is “0” during the period. Further, the scanning line driving circuit 130A sequentially outputs scanning line signals Y1,..., Yj, Yj + 1,.

  Next, the reset timing signal Cr becomes L level only during a period in which the scanning line 101 to be rewritten is selected. In this example, since the jth and j + 1th lines are rewritten, the reset timing signal Cr becomes L level (inactive) during the period in which the scanning line signals Yj and Yj + 1 are active. As described above, the selection circuit 1453 (see FIG. 8) outputs the common electrode voltage Vcom when the reset timing signal Cr is H level (active), and outputs the PWM signal when the reset timing signal Cr is L level. . Here, since the value of the image data D is “0”, the PWM signal is always inactive (L level).

  Accordingly, the reset voltage Vrest is supplied to all the data lines 102 during the period in which the jth and j + 1th scanning lines 101 are selected. In the selection period of the other scanning lines 101, the common electrode voltage Vcom is supplied to all the data lines 102.

  As a result, as shown in FIG. 14, the common electrode voltage Vcom is supplied to the pixel electrodes 104 in the first to j−1th rows and the j + 2 to mth rows. The reset voltage Vrest is supplied to the pixel electrodes 104 in the j-th row and the j + 1-th row. Therefore, the spatial state of the electrophoretic particle 3 is initialized in the pixels in the j-th row and the j + 1-th row. On the other hand, since the electric field is not generated even when the common electrode voltage Vcom is written to the pixel electrode 104, the spatial state of the electrophoretic particles 3 in the pixels of the first to j-1th rows and the j + 2 to mth rows. Does not change.

  Next, in the writing operation, the image signal processing circuit 300A outputs the valid image data D only for the line to be rewritten, and sets the value of the image data D to “0” for the other lines. Thereby, rewriting can be performed only in the j-th row and the j + 1-th row.

  Next, in the third aspect, a plurality of lines to be rewritten are reset at the same time, and then rewritten by a normal writing operation. In the second mode, the reset operation is sequentially performed for each row, such as resetting the j + 1th row after the jth row. If a scanning line driving circuit capable of simultaneously selecting a plurality of scanning lines 101 to be rewritten is used, it is possible to simultaneously reset. For example, as shown in FIG. 15, if only the scanning line signals Yj and Yj + 1 are simultaneously activated and the reset voltage Vrest is supplied to the data line 102, the jth and j + 1th lines to be rewritten as shown in FIG. Of course, they can be reset simultaneously. In the writing operation, the image data D that is valid only for the line to be rewritten by the image signal processing circuit 300A is output, and the data value is set to “0” for the other lines. Then, writing is performed in the same manner as the normal writing operation. Thereby, rewriting can be performed only in the j-th row and the j + 1-th row.

  Next, in the fourth mode, all the pixels are reset at the same time, and thereafter, a normal writing operation is performed to perform rewriting. FIG. 17 is a block diagram of the electrophoresis panel B according to the fourth aspect. The electrophoretic panel B has a TFT 105 provided for each column, and the scanning line driving circuit 130B can simultaneously activate all the scanning line signals Y1 to Ym. The configuration is the same as the electrophoresis panel A shown in FIG.

  In FIG. 17, the reset voltage Vrest is supplied to the source electrode of each TFT 105. A reset timing signal Cr is supplied to the gate electrode of each TFT 105. Further, the drain electrode of each TFT 105 is connected to each data line 102. When the reset timing signal Cr becomes active, all the TFTs 105 are simultaneously turned on, and the reset voltage Vrest is supplied to each data line 102. On the other hand, when the reset timing signal Cr becomes active, the scanning line driving circuit 130B activates all the scanning line signals Y1 to Ym simultaneously. Therefore, the reset voltage Vrest is written to all the pixel electrodes 104 during the active period of the reset timing signal Cr. Thereby, all the pixels are simultaneously reset.

  In this case, each source electrode of the TFT 105 may be grounded, and a positive voltage sufficient to initialize the common electrode voltage Vcom with reference to the ground potential may be supplied. That is, a voltage sufficient to initialize the other electrode may be applied with respect to the potential of either one of the pixel electrode 104 and the common electrode 201. The common electrode 201 may be divided to provide a plurality of divided electrodes (for example, an upper half and a lower half), and a voltage for initialization may be supplied to the divided electrode to which the image region to be rewritten belongs. .

<2: Second Embodiment>
<2-1: Overview of Second Embodiment>
In the first embodiment described above, when the screen is rewritten, after performing the reset operation shown on the right side of FIG. 18, the write operation shown in the center of FIG. 18 is performed to update the display screen. In this case, the spatial state of the electrophoretic particles 3 is initialized once. For example, if the dispersion medium 2 is colored black and the electrophoretic particles 3 are white, the entire screen is darkened (black) when the display is updated. Since human vision cannot detect short-term changes, if the period required for the reset operation is short, it is possible to display a moving image by updating the screen one after another.

  However, depending on the physical properties of the dispersion system 1, a long time may be required for the reset operation, and a change in luminance associated with the initialization of the electrophoretic particles 3 may be detected by a person.

  Therefore, in the electrophoretic display device of the second embodiment, first, the average position of the electrophoretic particles corresponding to the gradation to be displayed next, and the average position of the electrophoretic particles corresponding to the gradation currently being displayed. And second, a constant voltage is applied between the electrodes for a time corresponding to the difference. For example, it is assumed that the current gradation is 50% and is changed to 75% gradation. As shown in the center of FIG. 18, when the average position of the electrophoretic particles 3 is about ½ of the thickness direction of the dispersion 1, the display gradation is 50%. In order to change this gradation to 75%, it is necessary to move the average position of the electrophoretic particles 3 to about 3/4 in the thickness direction as shown on the right side of FIG. Therefore, a constant voltage is applied to the pixel electrode 104 for a period corresponding to the difference between the gradation to be displayed next and the current gradation. Thereby, since the electrophoretic particles 3 move to a position corresponding to the display gradation, the display screen can be updated. The point that the screen can be updated without performing the reset operation is important when displaying a moving image.

<2-2: Configuration of electrophoretic display device>
In the electrophoretic display device of the second embodiment, except that the image signal processing circuit 301A is used instead of the image signal processing circuit 300A, and the PWM circuit 145A is used instead of the PWM circuit 145 in the data line driving circuit 140A, The configuration is the same as the electrophoretic display device of the first embodiment shown in FIG.
<2-2-1: Image signal processing circuit>
FIG. 19 is a block diagram showing the configuration of the image signal processing circuit 301A. As shown in this figure, the image signal processing circuit 300A includes an A / D converter 310, a correction unit 320, and a calculation unit 330. An image signal VID supplied from the outside is converted into input image data Din via an A / D converter 310. The correction unit 320 has a ROM or the like. The correction unit 320 performs correction processing such as gamma correction on the input image data Din to generate image data Dv.

  Next, the arithmetic unit 330 includes a memory 331 and a subtracter 332. The image data Dv is supplied to one input terminal of the subtracter 332 and the memory 331. The memory 331 includes a first field memory 331A and a second field memory 331B. The first field memory 331A performs a write operation in an odd field while performing a read operation in an even field. The second field memory 331B performs a read operation in the odd field, while performing a write operation in the even field. This memory 331 delays the image data Dv by one field. The delayed image data Dv is supplied to the other input terminal of the subtractor 332 as delayed image data Dv ′. The subtractor 332 generates difference image data Dd by subtracting the delayed image data Dv ′ from the image data Dv, and outputs this. The MSB of the difference image data Dd is a sign bit, and indicates positive when the digit is “0” and negative when it is “1”.

  In the first field, since there is no delayed image data Dv ′, the other input terminal of the subtracter 332 is supplied with dummy data having a data value of “0”. . Therefore, in the first field, the image signal processing circuit 301A outputs the image data Dv as the difference image data Dd.

  Here, if the delayed image data Dv ′ is the current display gradation, the image data Dv corresponds to the gradation to be displayed next. Therefore, the difference image data Dd is data corresponding to the difference between the current gradation and the gradation to be displayed next. The difference image data Dd is supplied to the data line driving circuit 140A instead of the image data D.

<2-2-2: PWM circuit>
FIG. 20 is a block diagram showing a configuration of the PWM circuit 145A. The PWM circuit 145A differs from the PWM circuit 145 shown in FIG. 8 in that the data Db1 to Dbn are processed by dividing them into the most significant bit and other bits. In the PWM circuit 145A, the most significant bit of the data Db1 to Dbn is supplied to the selection circuit 1453A as the selection signal Ms. Data obtained by removing the most significant bit from the data Db1 to Dbn is supplied to the comparator 1451. The comparator 1451 compares the lower bit with the count data CNT to generate a comparison signal CS.

  The selection circuit 1453A selects a predetermined voltage from the common electrode voltage Vcom, applied voltage + Va, −Va, and reset voltage Vrest based on the PWM signals W1 to Wn, the reset timing signal Cr, and the selection signal Ms. Output.

  The selection conditions are as follows. First, the selection circuit 1453A selects the reset voltage Vrest when the reset timing signal Cr is active (H level). Second, the selection circuit 1453A selects the applied voltage + Va when the reset timing signal Cr is inactive (L level), the PWM signal is active (H level), and the selection signal Ms is H level. Third, the selection circuit 1453A selects the applied voltage −Va when the reset timing signal Cr is inactive (L level), the PWM signal is active (H level), and the selection signal Ms is L level. Fourth, the selection circuit 1453A selects the common electrode voltage Vcom when the reset timing signal Cr is inactive (L level) and the PWM signal is inactive (L level).

  Unlike the first embodiment, the selection circuit 1453A selects the applied voltages + Va and −Va based on the selection signal Ms for the following reason. In the first embodiment, when updating an image, the reset voltage Vrest is applied to the pixel electrode 104 to attract the electrophoretic particles 3 to the pixel electrode 104. For this reason, in the writing period Tw, the electrophoretic particles 3 may be moved from the pixel electrode 104 side to the common electrode 201 side. That is, the moving direction of the electrophoretic particles 3 in the writing period Tw is limited to one direction. On the other hand, in the second embodiment, since the position of the electrophoretic particle 3 is controlled based on the difference image data Dd, it is necessary to move the electrophoretic particle 3 in both directions. Therefore, based on the selection signal Ms, the positive voltage + Va and the negative voltage −Va can be selected based on the common electrode voltage Vcom.

<2-3: Operation of electrophoretic display device>
Next, the operation of the electrophoretic display device will be described. FIG. 21 is a timing chart showing the overall operation of the electrophoretic display device. The outline of the operation will be described with reference to this figure.

  First, when the power source of the electrophoretic display device is switched from the off state to the on state at time t0, power is supplied to the image signal processing circuit 301A, the timing generator 400A, and the electrophoretic display panel A. The timing generator 400A activates the reset timing signal Cr for one field period at time t1 when the predetermined period has elapsed and the circuit operation is stable. In the reset period Tr, the data line driving circuit 140A outputs the reset voltage Vrest to each data line 102. Further, the scanning line driving circuit 130 sequentially selects each scanning line 101. Thus, when the reset voltage Vrest is written to all the pixel electrodes 104, the electrophoretic particles 3 move to the pixel electrode 104 side. That is, the spatial state of the electrophoretic particles 3 is initialized.

  Next, when the time t2 is reached, the writing period Tw starts. In the writing period Tw, the image signal processing circuit 300A outputs the difference image data Dd. The applied voltage + Va or −Va is written in each pixel electrode 104 for a time corresponding to the difference between the gradation being displayed and the gradation to be displayed next. However, in the first field (from time t2 to time t3), the image data Dv is supplied as the differential image data Dd to the data line driving circuit 140A, so that the applied voltage is applied only during the period corresponding to the gradation to be displayed. + Va is written to each pixel electrode 104. However, since the display gradation is 0% (or 100%) by the reset operation, if attention is paid to the basic function, the gradation being displayed and the next display are displayed even in the first field. It can be said that the applied voltage + Va is written for a period corresponding to the difference from the power gradation.

<2-3-1: Write operation>
Next, the write operation will be described in detail. FIG. 22 is a timing chart of the electrophoretic display device in the writing operation. Here, the writing operation in the pixels of i rows (i th scanning line) and j columns (j th data line) will be described. Of course, similar writing is performed in other pixels. In this example, it is assumed that the pixel Pij displays a gradation level of 100% in the immediately preceding field. In addition, a solid line indicates a case where the gradation to be displayed in the current field is 50%, and a dashed line indicates a case where the gradation is 0%.

  The voltage of the data line signal Xj supplied to the jth data line 102 becomes the applied voltage + Va or −Va in the differential voltage application period Tdv shown in FIG. If the gradation to be displayed in the current field is 50%, it is reduced by 50% from the gradation of the previous field. For this reason, as shown in FIG. 22, the applied voltage −Va is selected in the differential voltage application period Tdv. On the other hand, the non-bias period Tdb is a period during which the PWM signal Wj is inactive.

Further, the scanning line signal Yi supplied to the i-th scanning line 101 becomes active during the i-th horizontal scanning period. The TFT 103 constituting the pixel Pij is turned on during the horizontal scanning period. The data line signal Xj from time T1 to time T3 is taken into the pixel electrode 104 of the pixel Pij. That is, in this example, the operation from writing the applied voltage −Va to the pixel electrode 104 to writing the common electrode voltage Vcom is completed in a certain selection period of a certain scanning line.
Since the image holding operation is the same as that in the first embodiment, description thereof is omitted.

<3: Third embodiment>
Next, an electrophoretic display device according to a third embodiment will be described. In the electrophoretic display device of the first embodiment, first, the applied voltage Va is applied to the pixel electrode 104 only for a period corresponding to the display gradation, and the electrophoretic particles 3 are applied for a distance corresponding to the gradation. Second, the common electrode voltage Vcom is applied to the pixel electrode 104 so as not to apply the Coulomb force to the electrophoretic particles 3. When the dispersion medium 2 has a small viscous resistance, the electrophoretic particles 3 migrate by inertia even after the common electrode voltage Vcom is applied. Therefore, the image data D is expected in the image signal processing circuit 300A in anticipation of inertia. Was generated.

  However, depending on the value of the viscous resistance of the dispersion medium 2, it may take a long time to attenuate the mobility energy of the electrophoretic particles 3. In the above-described example, since the electrophoretic particles 3 migrate from the pixel electrode 104 toward the common electrode 201, if the viscous resistance is extremely small, the display screen gradually becomes brighter and settles to a certain brightness.

  The third embodiment provides an electrophoretic display device that can prevent such fluctuations in the brightness of the display screen. The electrophoretic display device of the third embodiment is similar to that shown in FIG. 3 except that the image signal processing circuit 300B is used instead of the image signal processing circuit 300A and the data line driving circuit 140B is used instead of the data line driving circuit 140A. The same configuration as the electrophoretic display device of the first embodiment shown in FIG.

<3-1: Image signal processing circuit>
First, the image signal processing circuit 300B will be described. FIG. 23 is a block diagram of the image signal processing circuit 300B, and FIG. 24 is a timing chart of the output data.

  As shown in FIG. 23, the image signal processing circuit 300B includes an A / D converter 310, a correction unit 320, a braking data generation unit 330, and a selection unit 340. The A / D converter 310 converts the image signal VID from an analog signal to a digital signal and outputs input image data Din. The correction unit 320 includes a ROM or the like, and generates image data D by performing correction processing such as gamma correction on the input image data Din.

  The braking data generation unit 330 has a table therein. This table stores the data value of the braking data Ds in association with the data value that the image data D can take. The braking data generation unit 330 accesses the table using the image data D as an address to obtain the braking data Ds. The table includes a storage circuit such as a RAM or a ROM. Here, the braking data Ds is used to attenuate the movement of the electrophoretic particles 3. The braking data Ds corresponds to the braking voltage application period Ts.

  The electrophoretic particles 3 are given a Coulomb force by an electric field corresponding to the applied voltage Va. In the voltage application period Tv, the electrophoretic particles 3 are accelerated and migrated by the Coulomb force. Thereafter, even if the application of the electric field to the dispersion system 1 is stopped, the electrophoretic particles 3 continue to move due to inertia. In order to attenuate the movement, first, it is necessary to apply a reverse electric field. Secondly, the period in which the reverse electric field is to be applied is determined according to the kinetic energy of the electrophoretic particles 3, in other words, the gradation to be displayed. Therefore, in the present embodiment, braking data Ds considering the viscous resistance of the dispersion medium 2 and the like is generated in advance, and this is associated with the value of the image data D and stored in advance in the table. The braking data Ds is read from the table based on the above.

  Next, as shown in FIG. 24, the selection unit 340 outputs multiplexed data Dm obtained by multiplexing the image data D and the braking data Ds during the writing period. In this example, the image data D is 6 bits and the braking data Ds is 6 bits. The multiplexed data Dm is 12-bit data. In the multiplexed data Dm, 6 bits from the MSB are image data D, and 6 bits from the LSB are braking data Ds.

<3-2: Data line driving circuit>
Next, the data line driving circuit 140B will be described. The data line driving circuit 140B is configured similarly to the data line driving circuit 140A of the first embodiment except for the configuration of the PWM circuit 145B.

  FIG. 25 is a block diagram of a PWM circuit 145B used in the third embodiment, and FIG. 26 is a timing chart thereof. As shown in FIG. 25, the PWM circuit 145B includes unit circuits R1 to Rn. Each of the unit circuits R1 to Rn is different from the PWM circuit 145 of the first embodiment shown in FIG. 8 in that a comparator 1454 and an SR latch 1455 are added and a selection circuit 1456 is used instead of the selection circuit 1453. To do.

  The comparator 1451 constituting each of the unit circuits R1 to Rn is supplied with the image data D composed of the upper bits of the multiplexed data Dm, while the comparator 1454 receives the braking data Ds composed of the lower bits. Supplied. The comparator 1454 generates a comparison signal CS ′. The comparison signal CS ′ becomes active (H level) when the count data CNT and the braking data Ds match.

  Next, each SR latch 1455 sets the output level at the falling edge (H level) and resets at the rising edge (L level). Further, PWM signals W1 to Wn as output signals of the SR latches 1452 are supplied to the set terminal, and a comparison signal CS ′ is supplied to the reset terminal. The output signal of each SR latch 1455 is supplied to the selection circuit 1456 as the braking signals W1 ′ to Wn ′.

  Next, each selection circuit 1456 selects the reset voltage Vrest, the applied voltage Va, the braking voltage Vs, and the common electrode voltage Vcom based on the reset timing signal Cr, the PWM signals W1 to Wn, and the braking signals W1 ′ to Wn ′. A predetermined voltage is selected and output. The selection conditions are as follows.

  First, the selection circuit 1456 selects the reset voltage Vrest when the reset timing signal Cr is active (H level). Second, the selection circuit 1456 selects the applied voltage Va when the reset timing signal Cr is inactive (L level) and the PWM signal is active (H level). Third, the selection circuit 1456 selects the braking voltage Vs when the reset timing signal Cr is inactive (L level) and the braking signal is active (H level). Fourth, the selection circuit 1456 selects the common electrode voltage Vcom when the reset timing signal Cr, the PWM signal, and the braking signal are inactive (L level).

  Here, the operation of the j-th unit circuit Rj will be specifically described with reference to the timing chart shown in FIG. In this example, the reset timing signal Cr is inactive during a certain horizontal scanning period, and the line sequential image data Dbj includes image data D and braking data Ds. The gradation value indicated by the image data D in this example is “32”. Further, the value indicated by the braking data Ds in this example is “48”. As shown in this figure, the PWM signal Wj becomes H level during the period from the start of the horizontal scanning period until the value of the count data CNT becomes “32” (period from time t20 to time t21).

  Since SR latch 1455 is triggered by the falling edge of PWM signal Wj, braking signal Wj ′ transitions from the L level to the H level at time t21. Then, at time t22, the value of the count data CNT becomes “48”, and the value of the count data CNT matches the value of the braking data Ds. At this time, the comparison signal CS ′ transitions from the L level to the H level, and the braking signal Wj ′ transitions from the H level to the L level in synchronization with the rising edge.

  As described above, the selection circuit 1455 selects the applied voltage Va during the period in which the PWM signal Wj is at the H level, selects the braking voltage Vs during the period in which the braking signal Wj ′ is at the H level, and these signals are at the L level. During the period, the common electrode voltage Vcom is selectively output. Therefore, as shown in FIG. 26, the voltage of the data line signal Xj becomes the applied voltage Va in the period from time t20 to time t21, becomes the braking voltage Vs in the period from time t21 to time t22, and further, at time t22. Until the end of the horizontal scanning period until the end of the horizontal scanning period. The data line signals X1 to Xn generated in this way are supplied to each data line 102. The data line signals X1 to Xn are applied to the pixel electrode 104 in synchronization with the scanning line signals Y1 to Ym.

<3-3: Operation of the electrophoretic display device>
Next, the operation of the electrophoretic display device according to the third embodiment will be described. This electrophoretic display device operates in the order of reset operation → write operation → hold operation → rewrite operation (reset operation and write operation) in the electrophoretic display of the first embodiment described with reference to FIG. It is the same as the device. However, the operation of the electrophoretic display device according to the third embodiment includes a step of applying the braking voltage Vs to the pixel electrode 104 for a predetermined period during the write operation (including the rewrite operation). This is different from the operation of the electrophoretic display device according to the first embodiment. Hereinafter, the details of the writing operation as a difference will be described.

FIG. 26 is a timing chart of the electrophoretic display device in the writing operation. Here, the writing operation in the pixel Pij in i row and j column will be described. A similar writing operation is performed in other pixels.
The data line signal Xj is supplied to the jth data line 102. As shown in FIG. 26, the voltage of the data line signal Xj becomes the applied voltage Va in the voltage application period Tv. The voltage application period Tv is a period from time T1 to time T2. The voltage of the data line signal Xj becomes the braking voltage Vs in the braking voltage application period Ts. The braking voltage application period Ts is a period from time T2 to time T3. The voltage of the data line signal Xj becomes the common electrode voltage Vcom in the no-bias period Tb. The no-bias period Tb is a period from time T3 to time T4.

  Further, the scanning line signal Yi is supplied to the i-th scanning line 101. The scanning line signal Yi becomes active during the i-th horizontal scanning period. Therefore, the TFT 103 of the pixel Pij is turned on in the horizontal scanning period, and the data line signal Xj is applied to the pixel electrode 104 of the pixel Pij in the period from time T1 to time T4. That is, in this example, in a certain selection period of a certain scanning line, first, the applied voltage Va is written to the pixel electrode 104, secondly, the braking voltage Vs is written to the pixel electrode 104, and thirdly, the common electrode voltage is applied to the pixel electrode 104. Write Vcom.

  Next, the behavior of the electrophoretic particles 3 in the pixel Pij will be considered. Since the reset operation is performed before this writing operation, the electrophoretic particles 3 of the pixels Pij are all located on the pixel electrode 104 side at time T1. At this time, when the applied voltage Va is applied to the pixel electrode 104, an electric field is applied from the pixel electrode 104 toward the common electrode 201. Therefore, the electrophoretic particle 3 starts moving from time T1, and the luminance Iij gradually increases.

  Then, at time T2, the braking voltage Vs is applied to the pixel electrode 104. The application period of the braking voltage Vs is set according to the application period of the immediately preceding application voltage Va. The polarity of the braking voltage Vs is negative with respect to the common electrode voltage Vcom. This is because, during the voltage application period Tv, the electrophoretic particles 3 are subjected to a Coulomb force from the pixel electrode 104 toward the common electrode 201, and thus it is necessary to apply an electric field in a direction to cancel this. .

  The braking voltage Vs acts on the electrophoretic particles 3 as a brake. The braking voltage Vs gives the electrophoretic particles 3 a Coulomb force opposite to the direction of movement of the electrophoretic particles 3. As a result, the electrophoretic particles 3 stop moving by the end time T3 of the braking voltage application period Ts.

  At time T3, the common electrode voltage Vcom is applied to the pixel electrode 104. Then, since the voltages of the pixel electrode 104 and the common electrode 201 match, the charge accumulated in the pixel capacitor is discharged. Thereby, even if the TFT 103 is turned off, no electric field is generated in the pixel Pij, so that the spatial state of the electrophoretic particles 3 can be maintained.

  As described above, in the writing operation of the present embodiment, first, the applied voltage Va is written into the pixel electrode 104 of the pixel Pij for a period corresponding to the gradation to be displayed. Then, the electrophoretic particles 3 move. Further, the braking voltage Vs is written to the pixel electrode 104 of the pixel Pij for a predetermined period. Then, the movement of the electrophoretic particles 3 is attenuated and the electrophoretic particles 3 are stopped. Therefore, even when the viscosity resistance of the dispersion medium 2 is small, the migration distance due to the inertia of the electrophoretic particles 3 can be shortened. As a result, it is possible to display a stable image with no change in luminance in a short time.

<4: Fourth Embodiment>
The fourth embodiment is a combination of the technique related to differential driving described in the second embodiment and the technique related to braking of the electrophoretic particles 3 described in the third embodiment.
In the electrophoretic display device of the third embodiment, a constant voltage is applied to the pixel electrode only for a period corresponding to the gradation to be displayed. However, in the electrophoretic display device of the fourth embodiment, A constant voltage is applied to the pixel electrode over a period corresponding to the difference in gradation currently being displayed.

  The electrophoretic display device of the fourth embodiment uses the electric signal of the second embodiment except that the image signal processing circuit 301B is used instead of the image signal processing circuit 301A and the PWM circuit 145B is used instead of the PWM circuit 145A. The configuration is the same as the electrophoretic display device. Hereinafter, the difference will be mainly described.

<4-1: Image signal processing circuit>
First, the image signal processing circuit 301B will be described. FIG. 28 is a block diagram of the image signal processing circuit 301B. The image signal processing circuit 301B illustrated in FIG. 28 includes a braking data generation unit 350 and a selection unit 340 in the subsequent stage of the calculation unit 330, as compared with the image signal processing circuit 301A of the second embodiment illustrated in FIG. Is different.

  The braking data generation unit 350 includes a table. The table is configured by a storage circuit such as a RAM or a ROM. The table stores the data value of the braking data Dds in association with the data value that the difference image data Dd can take.

  Here, the braking data Dds is used to attenuate the movement of the electrophoretic particles 3. The value of the braking data Dds corresponds to a braking voltage application period Tds to be described later. As described above, the electrophoretic particles 3 are accelerated and migrated by the Coulomb force. Thereafter, even if the application of the electric field to the dispersion system 1 is stopped, the electrophoretic particles 3 continue to move due to inertia. In order to stop the electrophoretic particles 3, it is necessary to apply a reverse electric field. Further, the electric field strength needs to be determined according to the kinetic energy of the electrophoretic particles 3, in other words, the difference gradation value. Therefore, in the present embodiment, braking data Dds considering the viscous resistance of the dispersion medium 2 is generated in advance, and this is stored in advance in a table in association with the value of the difference image data Dd. The braking data Dds is read from the table based on the data Dd.

Next, the selection unit 340 selects the difference image data Dd and the braking data Dds, thereby generating multiplexed data Ddm obtained by multiplexing these. In this example, the multiplexed data Dm is 12-bit data, and the multiplexed data Dm is 6 bits from the MSB as differential image data Dd and 6 bits from the LSB is braking data Dds.
The selection operation of the selection unit 340 is the same as that in FIG. 24 in which the image data D is replaced with the differential image data Dd and the braking data Ds is replaced with the braking data Dds.

<4-2: PWM circuit>
FIG. 29 is a block diagram showing a configuration of the PWM circuit 145C. FIG. 30 is a diagram showing a relationship between the multiplexed data Ddm and data obtained by dividing the multiplexed data Ddm.
As shown in FIG. 29, the PWM circuit 145C includes unit circuits R1 to Rn. Multiple data Ddm is supplied to each unit circuit R1 to Rn as data Db1 to Dbn in a dot-sequential format. The multiplexed data Ddm includes differential image data Dd and braking data Dds as shown in FIG. Among the difference image data Dd, the most significant bit is the selection signal Ms, and the lower 5 bits excluding the most significant bit are the difference image data Dd ′. That is, the selection signal Ms and the difference image data Dd ′ are obtained by separating the sign bit (MSB) of the difference image data Dd and other bits indicating the absolute value. The most significant bit of the braking data Dds is the selection signal Ms ′, and the lower 5 bits excluding the most significant bit are the braking data Dds ′. That is, the selection signal Ms ′ and the difference image data Dd ′ are obtained by separating the sign bit (MSB) of the difference image data Dd and other bits indicating the size.

  Each unit circuit R1 to Rn includes a comparator 1451, a comparator 1454, and a selection circuit 1456. The comparator 1451 compares the 5-bit count data CNT and the difference image data Dd ′ to generate a comparison signal CS. The comparison signal CS ′ becomes active (H level) when the count data CNT matches the difference image data Dd ′. The comparator 1454 compares the count data CNT and the braking data Dds ′ to generate a comparison signal CS ′. The comparison signal CS ′ becomes active (H level) when the count data CNT matches the braking data Dds ′.

  Next, each selection circuit 1456, based on the reset timing signal Cr, the PWM signals W1 to Wn, the braking signals W1 ′ to Wn ′, the selection signals Ms and Ms ′, the reset voltage Vrest, the applied voltages + Va and −Va, and the stop A predetermined voltage is selected from the voltages + Vs, −Vs and the common electrode voltage Vcom and output.

  The selection conditions are as follows. First, the selection circuit 1456 selects the reset voltage Vrest when the reset timing signal Cr is active (H level). Second, the selection circuit 1456 selects the applied voltage + Va or −Va when the reset timing signal Cr is inactive (L level) and the PWM signal is active (H level). Third, the selection circuit 1456 selects the braking voltage + Vs or −Vs when the reset timing signal Cr is inactive (L level) and the stop signal is active (H level). Fourth, the selection circuit 1456 selects the common electrode voltage Vcom when the reset timing signal Cr, the PWM signal, and the stop signal are inactive (L level).

  Furthermore, when selecting the applied voltage + Va or −Va, the selection circuit 1456 selects the applied voltage −Va when the selection signal Ms is at the H level, and selects the applied voltage + Va when it is at the L level. In addition, when selecting the braking voltage + Vs or −Vs, the selection circuit 1456 selects the braking voltage −Vs when the selection signal Ms ′ is at the H level, and selects the braking voltage + Vs when it is at the L level.

  Here, the operation of the j-th unit circuit Rj will be specifically described with reference to the timing chart shown in FIG. In this example, the reset timing signal Cr is inactive during a certain horizontal scanning period. Further, the gradation value indicated by the difference image data Dd ′ is “16”, and the value indicated by the braking data Ds ′ is “24”. In addition, the selection signal Ms is “0” and the selection signal Ms ′ is “1”.

  The period in which the PWM signal Wj is at the H level is a period from the start of the horizontal scanning period until the value of the count data CNT becomes “16” (period from time t20 to time t21). Since SR latch 1455 is triggered by the falling edge of PWM signal Wj, braking signal Wj ′ transitions from the L level to the H level at time t21. Then, at time t22, the value of the count data CNT becomes “24”, which matches the value of the braking data Ds ′. At this time, the comparison signal CS ′ transitions from the L level to the H level, and the braking signal Wj ′ transitions from the H level to the L level in synchronization with the rising edge.

  As described above, the selection circuit 1456 selects the applied voltage + Va or −Va during the period in which the PWM signal Wj is at the H level, and selects the stop voltage + Vs or −Vs in the period in which the stop signal Wj ′ is at the H level. Since the selection signals Ms and Ms ′ are “0” and “1”, respectively, the selection circuit 1456 selects the applied voltage + Va and the braking voltage −Vs. Further, the common electrode voltage Vcom is selected when the PWM signal Wj and the braking signal Wj ′ are in the L level period. For this reason, the voltage of the data line signal Xj becomes the applied voltage + Va in the period from time t20 to time t21. The voltage of the data line signal Xj becomes the braking voltage −Vs in the period from time t21 to time t22. Further, the voltage of the data line signal Xj becomes the common electrode voltage Vcom from time t22 until the horizontal scanning period ends.

<4-3: Operation of electrophoretic display device>
This electrophoretic display device is the same as the electrophoretic display device according to the second embodiment described with reference to FIG. 21 in that it operates in the order of reset operation → write operation → hold operation. However, the difference is that a step of applying a braking voltage to the pixel electrode 104 is added during the writing operation. Hereinafter, the details of the writing operation as a difference will be described.

  FIG. 32 is a timing chart of the electrophoretic display device in the writing operation. Here, the writing operation in the pixel Pij in i row and j column will be described. Similar writing is performed in other pixels. In this example, it is assumed that the pixel Pij displays a gradation level of 100% in the immediately preceding field. In addition, a solid line indicates a gradation to be displayed in the current field of 0%, and a dashed line indicates a gradation of 50%.

  The voltage of the data line signal Xj becomes the applied voltage + Va or −Va in the differential voltage application period Tdv. If the gradation to be displayed in the current field is 50%, it is reduced by 50% from the gradation of the previous field. For this reason, as shown in FIG. 28, the applied voltage −Va is selected in the differential voltage application period Tdv. In the braking voltage application period Tds, the voltage of the data line signal Xj is the braking voltage + Vs. Further, in the no-bias period Tdb from time T3 to time T4, the voltage of the data line signal Xj becomes the common electrode voltage Vcom.

  Further, the scanning line signal Yi becomes active during the i-th horizontal scanning period. For this reason, the TFT 103 of the pixel Pij is turned on in the horizontal scanning period. The voltage of the data line signal Xj from time T1 to time T4 is applied to the pixel electrode 104 of the pixel Pij.

<5: Fifth embodiment>
Similar to the electrophoretic display device of the first embodiment, the electrophoretic display device of the fifth embodiment applies a voltage on the pixel electrode 104 for a period corresponding to the gradation value of the image data D. In the first embodiment, one horizontal scanning period is divided into a voltage application period Tv and a no-bias period Tb, and the movement and stop of the electrophoretic particles 3 are completed within one horizontal scanning period. In contrast, in the fifth embodiment, the applied voltage Va is applied to the pixel electrode 104 in units of horizontal scanning periods, and the common electrode voltage Vcom is applied to the pixel electrodes 104 in units of horizontal scanning periods. In the following description, the former is referred to as a voltage application period Tvf, and the latter is referred to as a non-bias period Tbf. Here, the voltage application period Tvf is composed of a plurality of horizontal scanning periods. The number of horizontal scanning periods is determined according to the gradation value indicated by the image data D.

  In the driving method of the present embodiment, the horizontal scanning period is divided into the first half period Ha and the second half period Hb, and different processing is performed in each period. First, in the first half period Ha of each horizontal scanning period, the scanning lines 101 are sequentially selected, and the applied voltage Va is written to the pixel electrodes 104 in each row. For example, the applied voltage Va is written in the pixel electrode 104 of the pixels Pi1, Pi2,..., Pim in the i-th row in the first half period Ha of the i-th horizontal scanning period.

  Next, in the second half period Hb of each horizontal scanning period, the common electrode voltage Vcom is appropriately written in each pixel electrode 104 according to the gradation to be displayed. For example, it is assumed that the gradation to be displayed on the pixel Pi2 in the i-th row and the second column is “3”. In this case, the common electrode voltage Vcom is written to the pixel in the second half period Hb of the (i + 3) th horizontal scanning period. As a result, an electric field is applied to the pixel Pi2 over three horizontal scanning periods from the i-th to the (i + 2) -th.

  Incidentally, in order to write a voltage to the pixel electrode 104 of the pixel Pij, the following two conditions must be satisfied. The first condition is to select the i-th scanning line 101 and turn on the TFT 103 of the pixel Pij. The second condition is that a predetermined voltage (Va or Vcom) is applied to the jth data line 102 in the selection period.

  However, when the i-th scanning line 101 is selected, not only the pixel Pij but all the TFTs 103 connected to the scanning line 101 are turned on. Therefore, when the common electrode voltage Vcom is written to the pixel Pij, the TFTs 103 of the other pixels Pi1 to Pij-1 and Pij + 1 to Pim are turned on in the second half period Hb of a certain horizontal scanning period. At this time, if any voltage is written in the other pixels Pi1 to Pij-1 and Pij + 1 to Pim, a desired gradation display cannot be obtained.

  Therefore, in the present embodiment, the data line 102 connected to the other pixels Pi1 to Pij-1 and Pij + 1 to Pim is set to a high impedance state. This prevents unnecessary voltage from being written to the pixel electrode 104.

  The electrophoretic display device of the fifth embodiment is the same as the electrophoretic display device of the first embodiment shown in FIG. 3 except for the following points. The differences are that an image signal processing circuit 300C is used instead of the image signal processing circuit 300A, a scanning line driving circuit 130C is used instead of the scanning line driving circuit 130A, and a data line driving circuit is used instead of the data line driving circuit 140A. 140C is used.

<5-1: Image processing circuit>
FIG. 33 is a block diagram showing a circuit configuration of the image signal processing circuit 300C. The image signal processing circuit 300C includes an A / D converter 310 and a correction unit 320. The A / D converter 310 converts the image signal VID into a digital signal. The correction unit 320 performs correction processing such as gamma correction and generates image data D. Here, the bit width of the image data D matches the total number of scanning lines 101. In this example, the number m of the scanning lines 101 is 64, and the bit width of the image data D is 6 bits.

  Further, the image signal processing circuit 300C includes a vertical counter 331, a horizontal counter 332, an adding circuit 333, a writing circuit 334, first and second field memories 335 and 336, and a reading circuit 338.

  The vertical counter 331 counts the first Y clock YCK1 and generates a row address Ay. The horizontal counter 332 counts the X clock XCK and generates a column address Ax. The row address Ay and the column address Ax specify the timing in one field where the current image data D is to be displayed. The addition circuit 333 adds the data value of the image data D and the row address Ay to generate an addition address Ay ′.

  The first memory 335 has a storage area of 128 (= 2m) rows and n columns as shown in FIG. Each storage area stores 1-bit data. The first memory 335 stores information indicating the timing at which the common electrode voltage Vcom is applied to the data line 102. Each column of the first memory 335 corresponds to each data line 102, and each row of the first memory 335 corresponds to the order of the horizontal scanning period.

  On the other hand, the second memory 336 has a storage area of 64 (= m) rows and 128 (= 2m) columns as shown in FIG. Each storage area stores 2-bit data. In the following description, an area for storing upper bits in a certain storage area is referred to as an upper bit storage area, and an area for storing lower bits in a certain storage area is referred to as a lower bit storage area. The data stored in the upper bit storage area instructs whether or not to select the scanning line 101 in the first half period Ha of the horizontal scanning period. The data stored in the lower bit storage area instructs whether or not to select the scanning line 101 in the second half period Hb of the horizontal scanning period. The scanning line 101 is driven based on data stored in the second memory 336. The stored contents of the first and second memories 335 and 336 are reset to “0” before the operation starts.

Next, the writing circuit 334 performs writing to the first memory 335 according to the following procedure. The write circuit 334 writes “1” to the storage area specified by specifying the row address as Ay ′ and the column address as Ax. The write circuit 334 writes data in the second memory 336 according to the following procedure. First, the write circuit 334 writes “1” in the upper bit storage area of the storage areas specified with the row address Ay and the column address Ay. Second, the write circuit 334 writes “1” in the lower bit storage area of the storage areas specified as the row address Ay and the column address Ay ′.

  Next, after the writing is completed, the read circuit 338 reads the first row, first column, first row, second column,..., Second row, first column, second row, second column,. , 64th row, first column,..., 128th row, nth column, sequentially read the storage contents of each storage area. Thus, the read circuit 338 generates 1-bit application time data Dx and supplies it to the data line driving circuit 140C.

  Further, the reading circuit 338 reads data from the second memory 336 according to the following procedure to generate scanning data Dy, and supplies the scanning data Dy to the scanning line driving circuit 130C. The read circuit 338 reads data from the second memory 336 in synchronization with the second Y clock YCK2. The frequency of the second Y clock YCK2 is 2 · m · fh (m = 64), where the horizontal scanning frequency is fh.

  First, the read circuit 338 sequentially reads data from the upper bit storage area of the first column and the first row, the upper bit storage area of the first column and the second row,..., The upper bit storage area of the first column and the 64th row. Next, data is sequentially read from the lower bit storage area of the first column and the first row, the lower bit storage area of the first column and the second row,..., The lower bit storage area of the first column and the 64th row. Thereafter, the read circuit 338 sequentially reads data from the storage areas from the second column to the 128th column, similarly to the first column.

  Therefore, in the j-th horizontal scanning period, the scan data Dy generated in the first half period Ha is the upper bit storage area of the j-th column and the first row, the upper bit storage area of the j-th column and the second row,. The data is read from the upper bit storage area of the 64th row and the jth column. Further, in the j-th horizontal scanning period, the scanning data Dy generated in the latter half period Hb includes the following bit storage area in the j-th column and the first row, the lower bit storage area in the j-th column and the second row,. The data is read from the lower bit storage area of the 64th row and the jth column.

  Here, the operation of the image signal processing circuit 300C will be specifically described by taking as an example the case where the row address Ay is “i”, the column address Ax is “j”, and the value of the image data D is “3”. Note that the image data D indicates the gradation of the pixel Pij in i row and j column.

  First, the write circuit 334 writes “1” in the upper bit storage area of i rows and i columns in the second memory 336. Further, the write circuit 334 writes “1” in the lower bit storage area of i row i + 3 column as shown in FIG. As described above, the i-th row of the second memory 336 corresponds to the i-th scanning line 101. The i-th column of the second memory 336 corresponds to the i-th horizontal scanning period, and the i + 3-th column corresponds to the i + 3 horizontal scanning period. Further, the lower bit storage area corresponds to the second half period Hb of the horizontal scanning period. Accordingly, “1” written in the lower bit storage area of i row i + 3 column indicates that the i-th scanning line 101 is selected in the second half period Hb of the i + 3 horizontal scanning period.

  The write circuit 334 writes “1” in the storage area of the (i + 3) th row and the jth column in the first memory 335. Each storage area in the jth column corresponds to the jth data line 102, and each storage area in the i + 3th row corresponds to the i + 3th horizontal scanning period. Therefore, “1” written in the storage area of the (i + 3) th row and the jth column indicates that the common electrode voltage Vcom is applied to the jth data line 102 in the second half period Hb of the (i + 3) th horizontal scanning period. To do.

  Therefore, the applied voltage Va is applied to the pixel electrode 104 of the pixel Pij for a period from the start of the i-th horizontal scanning period to the end of the first half period Ha of the i + 3th horizontal scanning period. When the second half period Hb of the (i + 3) th horizontal scanning period starts, the common electrode voltage Vcom is applied to the pixel electrode 104 of the pixel Pij. As a result, the applied voltage Va can be applied to the pixel electrode 104 only during a period corresponding to the gradation value indicated by the image data D.

<5-2: Scanning line driving circuit>
Next, the scanning line driving circuit 130C will be described. FIG. 36 is a block diagram showing a configuration of the scanning line driving circuit 130C, and FIGS. 37 and 38 are timing charts thereof. In this example, it is assumed that the number m of scanning lines 101 is 64. The scanning line driving circuit 130C includes a Y shift register 131, switches SW1 to SW64, a first latch 132, and a second latch 133.

  The Y shift register 131 sequentially shifts the transfer start pulse DY ′ based on the second Y clock YCK2 and the inverted second Y clock YCK2B to generate sampling pulses SR1, SR2,. Since the frequency of the second Y clock YCK2 is selected to be 2 · m · fh (m = 64), as shown in FIG. 37, one set of sampling pulses SR1, SR2,. Generated. Accordingly, 64 scan data Dy are sequentially sampled by the switches SW1 to SW64 in a certain 1/2 horizontal scanning period. The first latch 132 holds the sampling result. The first latch 132 outputs the output data Dy1 to Dy64 shown in FIG. The second latch 133 latches the output data Dy1 to Dy64 based on the latch pulse LAT ′. As shown in FIG. 38, the latch pulse LAT ′ is a pulse having a period of ½ horizontal scanning period. The output signal of the second latch 133 is supplied to each scanning line 101 as scanning line signals Y1 ′ to Y64 ′.

  For example, as shown in FIG. 35, if the lower bit storage area of the i-th row and i + 3 column of the second memory 336 stores “1”, the output data Dyi to Dyi + 3 of the first latch 132 is 38. When these are latched by the latch pulse LAT ′ shown in FIG. 38, the scanning line signals Yi to Yi + 3 shown in FIG. 38 are obtained. That is, the scanning line signal Yi ′ output to the scanning line 101 in the i-th row becomes active in the first half period Ha in the i-th horizontal scanning period and also in the second half period Hb of the i + 3th horizontal scanning period. Becomes active.

<5-3: Data line driving circuit>
Next, the data line driving circuit 140C will be described. FIG. 39 is a block diagram showing a configuration of the data line driving circuit 140C. The data line driving circuit 140C is configured similarly to the data line driving circuit 140A shown in FIG. 6 except for the following points. The difference is that the application time data Dx is supplied instead of the image data D, the bus BUS, the first and second latches 142C and 143C are configured by 1 bit, and the PWM circuit instead of the PWM circuit 145 144C is used.

The first latch 142C converts the application time data Dx into dot sequential application time data Dax1 to Daxn. The second latch 143C converts the dot sequential application time data Dax1 to Daxn into line sequential application time data Dbx1 to Dbxn.
The PWM circuit 144C includes n selection units U1 to Un. The selection units U1 to Un select a predetermined voltage from the reset voltage Vrest, the applied voltage Va, and the common electrode voltage Vcom based on the reset timing signal Cr, the first Y clock YCK1, and the applied time data Dbx1 to Dbxn. Output.

  FIG. 40 is a truth table showing the output state of the jth selection unit Uj. The same applies to other units. As is apparent from this truth table, when the reset timing signal Cr is active (H level), the data line signal Xj becomes the reset voltage Vrest.

  Next, when the reset timing signal Cr is inactive (L level), the selection unit Uj performs selection based on the first Y clock YCK1 and the application time data Dbj. One cycle of the first Y clock YCK1 is a horizontal scanning period cycle.

  FIG. 41 is a timing chart showing the relationship between the data line signal Xj and the first Y clock YCK1 when the reset timing signal Cr is inactive. As shown in this figure, in the first half period Ha in the horizontal scanning period, the first Y clock YCK1 is at the H level. As shown in the truth table, the data line signal Xj becomes the applied voltage Va regardless of the logic level of the applied time data Dbj. That is, if the reset timing signal Cr is inactive, the voltage of all the data lines 102 becomes the applied voltage Va in the first half period Ha in the horizontal scanning period.

  On the other hand, in the second half period Hb, the first Y clock YCK1 becomes L level. In this case, the voltage of the data line signal Xj is determined based on the application time data Dbj. The data line signal Xj is at the common electrode voltage Vcom when the application time data Dbj is at the H level, and is in a high impedance state when the application time data Dbj is at the L level. That is, in the second half period Hb, unless the application time data Dbj becomes H level, the jth data line 102 is in a high impedance state. Therefore, if the application time data Dbj is at the L level, no voltage is applied to each pixel electrode 104 corresponding to the jth data line 102 even if the scanning signal becomes active.

<5-4: Operation of electrophoretic display device>
FIG. 42 is a timing chart showing the overall operation of the electrophoretic display device. First, in the reset period Tr, the electrophoretic particles 3 are attracted to the pixel electrode 104 side, and the spatial state thereof is initialized.
Next, the writing period Tw includes a voltage application period Tvf and a no-bias period Tbf. In the voltage application period Tvf, the application voltage Va is written to each pixel electrode 104 for a predetermined time based on the application time data Dx output from the image signal processing circuit 300C. On the other hand, in the non-bias period Tbf, the common electrode voltage Vcom is applied to the pixel electrode 104.
Next, in the holding period Th, an electric field is not generated between the pixel electrode 104 and the common electrode 201, and an image written in the immediately preceding writing period is held.
In the rewrite period Tc, a series of processes such as reset → application of gradation voltage → no bias (application of common electrode voltage) is performed as in the first image display.

Next, a writing operation (including a rewriting operation) of the electrophoretic display device according to the fifth embodiment will be described in detail. FIG. 43 is a timing chart showing an operation example of the electrophoretic display device in the writing operation.
In this example, the image data D corresponding to the pixel Pij in the i-th row and j-th column is represented by Dij. Further, it is assumed that Dij = 2, Dij + 1 = 0, Dij + 2 = 3, and Dij + 3 = 2. Since the addition address Ay ′ is obtained by adding the row address Ay and the image data D, the value of the addition address Ay ′ changes as “i + 2” → “i” → “i + 3” → “i + 2”. Then, the data shown in the figure is stored in the storage area of the i-th row of the second memory 336. Data stored in the upper bit storage area corresponds to the scanning signal in the first half period Ha, and data stored in the lower bit storage area corresponds to the scanning signal in the second half period Hb. For this reason, the i-th scanning signal Yi is as shown in FIG. In the figure, Ti to Ti + 3 indicate the i-th to Ti + 3th horizontal scanning period. On the other hand, the voltages of the data line signals Xj to Xj + 2 are as shown in FIG. However, “Hi” indicates a high impedance state.

  Here, the voltage Vij of the pixel electrode 104 in i row and j column is considered. The i-th scanning line 101 is selected in the horizontal scanning period Ti, and the data line signal Xj becomes the voltage Va in the first half period Hai. Therefore, the voltage Vij becomes Va in the period Hai. In the period Hbi, the i-th scanning line 101 is selected, but in the period Hbi, the data line signal Xj is in a high impedance state. Therefore, the voltage Vij does not change in the period Hbi. In addition, the i-th scanning line 101 is not selected in the periods Hai + 1, Hbi + 1, and Hai + 2. Therefore, the voltage Vij does not change during these periods. When the i-th scanning line 101 is selected in the period Hbi + 2, the voltage Vcom of the data line signal Xj is applied to the pixel electrode 104 in i row and j column. Therefore, the voltage Vij becomes the voltage Vcom in the period Hbi. The voltage Vij becomes Va during a period of 2.5H.

  The voltage Vij + 1 of the pixel electrode 104 in the i row j + 1 column becomes the voltage Va in the period Hai. Thereafter, when the data line signal Xj + 1 becomes the voltage Vcom in the period Hbi, the voltage Vij + 1 becomes the voltage Vcom. The voltage Vij + 1 becomes Va during a period of 0.5H. Further, the voltage Vij + 2 of the pixel electrode 104 in the i row j + 2 column becomes the voltage Va in the period Hai. Thereafter, when the data line signal Xj + 2 becomes the voltage Vcom in the period Hbi + 3, the voltage Vij + 2 becomes the voltage Vcom. The voltage Vij + 2 becomes Va during a period of 3.5H.

  Except for the period Hai (= 0.5H), the periods in which the values of the voltages Vij, Vij + 1, and Vij + 2 are Va are 2H, 0H, and 3H. That is, the voltage Va is applied to the pixel electrode 104 for a period corresponding to the value of the image data D in units of horizontal scanning periods.

  Next, a writing operation when displaying 100% gradation and 50% gradation on the pixel Pij will be described with reference to FIG. Data line signal Xj is a signal of one horizontal scanning period in the first field. However, the data line signal Xj is the common electrode voltage Vcom in the second half period Hb, but as described with reference to FIG. 35, the data line signal Xj may be in a high impedance state in the second half period Hb. For example, the common electrode voltage Vcom may be obtained.

  Here, if the gradation to be displayed on the pixel Pij is 100%, the signal waveform of the scanning line signal Yi ′ changes as shown by a solid line in FIG. In this case, first, in the first field, the scanning line signal Yi ′ becomes active in the first half period Ha of the i-th horizontal scanning period. In this example, since the gradation to be displayed is 100%, the addition address Ay ′ is “i + 64”. For this reason, the scanning line signal Yi ′ becomes active next after 64 horizontal scanning periods have elapsed. That is, after one field period elapses, the scanning line signal Yi ′ becomes active.

  When the scanning line signal Yi ′ becomes active (H level) during the period from time T1 to time T2, the applied voltage Va is written to the pixel electrode 104 of the pixel Pij. Thereby, the voltage of the pixel electrode 104 transits from the reset voltage Vrest to the applied voltage Va at time T1. Then, a constant electric field is applied to the dispersion system 1.

At time T2, when the scanning line signal Yi becomes inactive (L level), the TFT 103 of the pixel Pij is turned off. However, since the pixel capacitor accumulates electric charges, the voltage Vij of the pixel electrode 104 maintains the applied voltage Va. In the next field, the scanning line signal Yi becomes active in the second half period Hb (time T4 to time T5) of the i-th horizontal scanning period. At this time, since the data line signal Xj is the common electrode voltage Vcom, the common electrode voltage Vcom is applied to the pixel electrode 104. As a result, the voltage Vij of the pixel electrode 104 coincides with the common electrode voltage Vcom when time T4 is reached.
That is, the voltage application time Tvf is determined according to the gradation value indicated by the image data D. Then, after this voltage application time Tvf, there is a non-bias period Tbf in which the common electrode voltage Vcom is applied.

Next, the behavior of the electrophoretic particles 3 in the pixel Pij will be considered. At time T0, the electrophoretic particles 3 of the pixels Pij are all located on the pixel electrode 104 side. This is because the reset operation is performed before the write operation. When the applied voltage Va is applied to the pixel electrode 104 at time T <b> 1, an electric field is applied from the pixel electrode 104 toward the common electrode 201. Therefore, the electrophoretic particles 3 start to move from time T1, and the luminance Iij gradually increases.
The electric field corresponding to the applied voltage Va is applied only for a period corresponding to the gradation. If a gradation of 100% is displayed, it is applied during one field period from time T1 to time T4. If a 50% gradation is displayed, an electric field is applied only for a 1/2 field period.

  In the first embodiment, the applied voltage Va is applied in a predetermined period of one horizontal period, but in the fifth embodiment, the applied voltage Va is applied in units of horizontal scanning periods. The amount of movement of the electrophoretic particles 3 is determined according to the strength of the electric field applied to the dispersion system 1 and the application time. In this example, since the electric field is applied for a long time, the desired luminance Iij can be obtained even if a weak electric field is applied. Therefore, according to this embodiment, it is possible to drive the data line 102 with the data line signals X1 to Xn at a low voltage.

<5-5: Modification of Fifth Embodiment>
In the fifth embodiment, as shown in FIG. 42, the writing period Tw is composed of a voltage application period Tvf and a no-bias period Tbf. However, the writing period Tw may be configured by a voltage application period Tvf, a braking voltage application period Tsf, and a no-bias period Tbf.

FIG. 45 is a timing chart showing the operation during the writing period of the electrophoretic display device according to the modification of the fifth embodiment. Note that just before the writing period Tw, the spatial state of the electrophoretic particles 3 is initialized as in the fifth embodiment.
The second half period Hb is divided into a first second half period Hb1 and a second second half period Hb2. The data line signal Xj is in a high impedance state or the braking voltage Vs in the first second half period Hb1. Further, the data line signal Xj becomes a high impedance state or the common electrode voltage Vcom in the second second half period Hb2. In the applied voltage period Tvf, the voltage Vij of the pixel electrode 104 becomes the applied voltage Va. During this period, the electrophoretic particles 3 start to move, and the luminance Iij gradually increases. Next, in the braking voltage application period Tsf from time T4 to time T6, the braking voltage Vs is applied to the pixel electrode 104.

  Since the braking voltage Vs is a negative voltage with respect to the common electrode voltage Vcom, a force in the direction opposite to the movement direction acts on the electrophoretic particles 3. Thereby, the moving speed of the electrophoretic particles 3 can be reduced, and the movement can be completely stopped by the time T6. In this modification, since the applied voltage Va and the braking voltage Vs are applied to the pixel electrode 104 in units of horizontal scanning periods, the data line signals X1 to Xn can be driven with a low voltage.

<6: Sixth Embodiment>
In the fifth embodiment, a constant voltage is applied to the pixel electrode 102 only for a period corresponding to the gradation to be displayed. Instead, a difference between the gradation to be displayed next and the gradation currently being displayed is applied instead. You may apply over the period corresponding to. Hereinafter, the difference will be mainly described.

<6-1: Image Processing Circuit>
First, the image signal processing circuit 301C will be described. FIG. 46 is a block diagram showing a configuration of the image signal processing circuit 301C. As shown in this figure, the image signal processing circuit 301C is configured similarly to the image processing circuit 301A shown in FIG. 19 except for the following points. The difference is that a vertical counter 341, a horizontal counter 342, an adder circuit 343, a write circuit 344, first and second memories 345 and 346, and a read circuit 348 are provided at the subsequent stage of the arithmetic unit 330. Note that the bit width of the difference image data Dd matches the total number of scanning lines 101. In this example, it is assumed that there are 64 scanning lines 101 and the bit width of the difference image data Dd is 6 bits. The MSB of the difference image data Dd is a sign bit. When the data value of the image data Dv is greater than or equal to the data value of the delayed image data Dv ′, the sign bit is “0”. On the other hand, when the data value of the image data Dv is less than the data value of the delayed image data Dv ′, the sign bit is “1”.

  The vertical counter 341 generates a row address Ay by counting the first Y clock YCK1. The horizontal counter 342 counts the X clock XCK and generates a column address Ax. The row address Ay and the column address Ax specify the timing in one field where the current difference image data Dd is to be displayed. The addition circuit 343 adds the difference image data Dd and the row address Ay to generate an addition address Ay ′.

  Next, the first memory 345 has a storage area of 128 (= 2m) rows and n columns as shown in FIG. Each storage area includes an upper bit storage area and a lower bit storage area. The upper bit storage area stores the sign bit (MSB) of the difference image data Dd. The lower bit storage area stores data indicating the timing at which the common electrode voltage Vcom is applied to the data line 102. Each column of the first memory 335 corresponds to each data line 102, and each row of the first memory 335 corresponds to the order of the horizontal scanning period. The second memory 346 is the same as the second memory 336 shown in FIG.

  Next, the writing circuit 344 writes to the first memory 345 in the following procedure. The write circuit 344 writes the sign bit (MSB) of the difference image data Dd in the upper bit storage area of the storage area specified with the row address Ay and the column address Ax. The write circuit 344 writes “1” in the lower bit storage area of the storage area specified and specified as the row address Ay ′ and the column address Ax. Note that data writing to the second memory 346 is the same as data writing to the second memory 336 described in the fifth embodiment.

  Next, after the writing is completed, the reading circuit 348 reads the first row, first column, the first row, second column,..., The second row, first column, the second row, second column,. , 64th row, first column,..., 128th row and nth column in the order of reading data from each storage area. The read data is 2-bit polarity / time data Ddx. The upper bit of the polarity / time data Ddx is a sign bit of the difference image data Dd, and indicates the polarity of the voltage to be applied to the pixel electrode 104. The lower bits of the polarity / time data Dx indicate the timing at which the common electrode voltage Vcom should be applied to the pixel electrode 104. The operation for reading data from the second memory 346 is the same as the operation for reading data from the second memory 336 described in the fifth embodiment.

<6-2: Data line driving circuit>
Next, the data line driving circuit 140D will be described. FIG. 48 is a block diagram showing a configuration of the data line driving circuit 140D. The data line driving circuit 140D is the same as the data line driving circuit 140C of the fifth embodiment shown in FIG. 39 except for the following points. The difference is that the polarity / time data Ddx is supplied instead of the application time data Dx, the bus BUS, the first and second latches 142D and 143D are composed of 2 bits, and the PWM circuit 144C is replaced. The point is that the PWM circuit 144D is used.

  The PWM circuit 144D includes n selection units U1 to Un. The selection units U1 to Un select a predetermined voltage from the reset voltage Vrest, applied voltage + Va, −Va, and common electrode voltage Vcom based on the reset timing signal Cr, the first Y clock YCK1, and the polarity / time data Dbx1 to Dbxn. Select to output.

  FIG. 49 is a truth table showing the selection operation of the jth selection unit Uj. The same applies to other selection units. As is apparent from this truth table, when the reset timing signal Cr is active (H level), the data line signal Xj becomes the reset voltage Vrest.

  Next, when the reset timing signal Cr is inactive (L level), the selection unit Uj performs selection based on the first Y clock YCK1 and the polarity / time data Dbj. FIG. 50 is a timing chart of the data line signal Xj and the Y clock YCK when the reset timing signal Cr is inactive. When the first Y clock YCK1 is at the H level, the selection unit Uj selects one of the applied voltages + Va and −Va based on the upper bits of the polarity / time data Dbj. Therefore, in the first half period Ha, the voltage of the data line signal Xj becomes the applied voltage + Va or −Va. The solid line shown in FIG. 50 indicates the data line signal Xj when the upper bit is at the L level. When the first Y clock YCK1 is at L level, the selection unit Uj performs selection based on the lower bits of the polarity / time data Dbj. Therefore, in the second half period Hb, when the lower bit of the polarity / time data Dbj is at the H level, the data line signal Xj becomes the common electrode voltage Vcom, while when the lower bit of the polarity / time data Dbj is at the L level, the data The line signal Xj is in a high impedance state.

<6-3: Operation of electrophoretic display device>
FIG. 51 is a timing chart showing the overall operation of the electrophoretic display device. First, in the reset period Tr, the electrophoretic particles 3 are attracted to the pixel electrode 104 side, and the spatial state thereof is initialized.
Next, the writing period Tw is composed of a plurality of unit periods. One unit period is composed of a set of a voltage application period Tvf and a non-bias period Tbf. In the voltage application period Tvf, the applied voltage + Va or −Va is written to each pixel electrode 104 for a predetermined time based on the polarity / time data Dx. On the other hand, in the non-bias period Tbf, the common electrode voltage Vcom is applied to the pixel electrode 104.
Next, in the holding period Th, an electric field is not generated between the pixel electrode 104 and the common electrode 201, and an image written in the immediately preceding writing period is held.

FIG. 52 is a timing chart of the electrophoretic display device in the writing operation. Here, the writing operation in the pixel Pij in i row and j column will be described. In this example, the gradation of the unit period immediately before in the pixel Pij is 10%, and 100% gradation is displayed in the current unit period.
In the first half period Ha of the horizontal scanning period, the voltage polarity of the data line signal Xj is determined depending on which one of the grayscale being displayed and the grayscale to be displayed is larger. In this example, since the gradation is increased from 10% to 100%, the data line signal Xj becomes the voltage + Va in the first half period Ha of the i-th horizontal scanning period.

First, the scanning line signal Yi ′ becomes active in the first half period Ha of the i-th horizontal scanning period in the first field. In this example, since the gradation increases by 90%, the scanning line signal Yi ′ becomes active again at time T3 when 0.9 field has elapsed from time t1.
When the scanning line signal Yi ′ becomes active (H level) during the period from time T1 to time T2, the applied voltage + Va is written to the pixel electrode 104 of the pixel Pij. The voltage Vij of the pixel electrode 104 changes from the common electrode voltage Vcom to the applied voltage + Va at time T1. During the period when the scanning line signal Yi becomes active again (time T3 to T4), the data line signal Xj becomes the common electrode voltage Vcom. Therefore, the voltage Vij of the pixel electrode 104 coincides with the common electrode voltage Vcom when the time T3 is reached.

  Next, the behavior of the electrophoretic particles 3 in the pixel Pij will be considered. Since the pixel Pij displays a gradation of 10% in the immediately preceding unit period, the electrophoretic particles 3 of the pixel Pij are located slightly closer to the common electrode 201 than the pixel electrode 104 at time T0. When the applied voltage + Va is applied to the pixel electrode 104 at time T <b> 1, an electric field is applied from the pixel electrode 104 toward the common electrode 201. Therefore, the electrophoretic particle 3 starts moving from time T1, and the luminance Iij gradually increases. The electric field corresponding to the applied voltage + Va is generated only for a period corresponding to the differential gradation. In this example, since the gradation is changed from 10% to 100%, the period during which the electric field is generated is 0.9 field.

  In the second embodiment, the applied voltage + Va or −Va is applied in a predetermined period of one horizontal period, but in the sixth embodiment, the applied voltage + Va or −Va is applied to the pixel electrode 102 in units of horizontal scanning periods. Applied. The amount of movement of the electrophoretic particles 3 is determined according to the strength of the electric field applied to the dispersion system 1 and the application time. In this example, since the electric field is applied for a long time, the desired luminance Iij can be obtained even if a weak electric field is applied. Therefore, according to the present embodiment, the data line signals X1 to Xn can be driven with a low voltage.

<6-4: Modification of Sixth Embodiment>
In the sixth embodiment, as shown in FIG. 51, the unit period Tu is composed of a voltage application period Tvf and a no-bias period Tbf. However, the unit period Tu may be constituted by a voltage application period Tvf, a braking voltage application period Tsf, and a no-bias period Tbf.

FIG. 53 is a timing chart showing an operation in the unit period Tu of the electrophoretic display device according to the modified example of the sixth embodiment. Also in this example, the second half period Hb is divided into the first second half period Hb1 and the second second half period Hb2 as in the modification of the fifth embodiment. However, the data line signal Xj is in the high impedance state, the braking voltage + Vs, or −Vs in the first second half period Hb1. + Vs and −Vs use the common electrode voltage Vcom as the center voltage. The reason why + Vs and −Vs having different polarities can be selected as the braking voltage is that the electrophoretic particles 3 move in two directions. That is, when + Va is selected as the applied voltage, -Vs is selected as the braking voltage, and when -Va is selected as the applied voltage, + Vs is selected as the braking voltage.
<7: Application example>
As mentioned above, although one Embodiment of this invention was described, this invention is not limited to this, Application and deformation | transformation are possible in the range which does not deviate from the meaning.
<7-1: Display of moving image>
In each of the above-described embodiments, one image is formed in the order of the reset operation and the writing operation and is retained, and the rewriting operation is performed as necessary. Therefore, the electrophoretic display device of each embodiment is suitable for displaying a still image. However, it is a matter of course that a moving image may be displayed by shortening the reset period Tr and repeating the rewrite operation at a certain cycle. When displaying a moving image, first, it is desirable that the moving speed of the electrophoretic particles 3 is high. For this reason, it is preferable that the viscosity resistance of the dispersion medium 2 is small. In such a case, even if the application of an electric field to the dispersion system 1 is stopped, the electrophoretic particles 3 often migrate by inertia. Therefore, it is preferable to apply the braking voltage Vs to attenuate the movement of the electrophoretic particles 3.

<7-2: Refresh period>
Although it is preferable that the specific gravity of the dispersion medium 2 and the electrophoretic particles 3 constituting the dispersion system 1 is equal, it is difficult to make the specific gravity of the two completely coincide with each other due to restrictions and variations in materials. In such a case, once an image is written and left for a long time, gravity may act on the electrophoretic particles 3 and the particles 3 may settle and float. Therefore, it is preferable to provide the timer device shown in FIG. 54 inside the timing generator 400C and rewrite the same image at a predetermined cycle.

The timer device 410 includes a timer unit 411 and a comparison unit 412.
The timer unit 411 measures the time to generate the duration data Dt, and when either one of the write start signal Ws and the rewrite signal Ws ′ instructing normal writing becomes active, the duration data Dt. The value of is reset to '0'. The comparison unit 412 compares the continuation time data Dt with the reference time data Dref indicating a predetermined refresh period, compares the continuation time data Dt with the reference time data Dref. A rewrite signal Ws ′ is generated.

FIG. 55 is a timing chart of the timer device 410. When the write start signal Ws becomes active, the duration data Dt of the timer unit 411 is reset and measurement is started. When a predetermined refresh period elapses, the continuation time data Dt and the reference time data Dref coincide with each other, and the rewrite signal Ws ′ becomes active. Thereafter, every time the refresh period elapses, the rewrite signal Ws ′ becomes active. On the other hand, if the write start signal Ws becomes active halfway, measurement of the refresh period starts from that point.
The display image can be refreshed by executing the rewriting operation (however, the same image) described in the above-described embodiment using the rewrite signal Ws ′ obtained in this way as a trigger.

<7-3: Electronic device>
Next, an electronic apparatus using the above-described electrophoretic display device will be described.
<7-3-1: Electronic book>
First, an example in which an electrophoretic display device is applied to an electronic book will be described. FIG. 56 is a perspective view showing this electronic book. In the figure, an electronic book 1000 includes an electrophoretic display panel 1001, a power switch 1002, a first button 1003, a second button 1004, and a CD-ROM slot 1005.

  When the user presses the power switch 1002 to insert a CD-ROM into the CD-ROM slot 1005, the contents of the CD-ROM are read and a menu is displayed on the electrophoretic display panel 1001. When the user operates the first button 1003 and the second button 1004 to select a desired book, the first page is displayed on the electrophoretic display panel 1001. The second button 1004 is pressed to advance the page, and the first button 1003 is pressed to return the page.

  In the electronic book 1000, after displaying the contents of the book, the display screen is updated only when the first button 1003 and the second button 1004 are operated. As described above, the electrophoretic particles 3 do not migrate unless an electric field is applied. In other words, no power supply is required to maintain the display image. Therefore, only when the display screen is updated, the electrophoretic display panel 1001 is driven by supplying voltage to the drive circuit. As a result, power consumption can be significantly reduced as compared with the liquid crystal display device.

  The display image on the electrophoretic display panel 1001 is displayed by the electrophoretic particles 3 that are pigment particles. Therefore, the display screen does not shine. Therefore, the electronic book 1000 can display the same as a printed matter, and has an advantage of less eye fatigue even when read for a long time.

<7-3-2: Personal computer>
Next, an example in which the electrophoretic display device is applied to a mobile personal computer will be described. FIG. 57 is a perspective view showing the configuration of this personal computer. In the figure, a computer 1200 includes a main body 1204 having a keyboard 1202 and an electrophoretic display panel 1206. Since the display image of the electrophoretic display panel 1206 is displayed by the electrophoretic particles 3 which are pigment particles, a backlight required for a transmissive / semi-transmissive liquid crystal display device is unnecessary. Therefore, the computer 1200 can be reduced in size and weight, and the power consumption can be greatly reduced.

<7-3-3: Mobile phone>
Further, an example in which the electrophoretic display device is applied to a mobile phone will be described. FIG. 58 is a perspective view showing the configuration of this mobile phone. In the figure, a mobile phone 1300 includes an electrophoretic display panel 1308 in addition to a plurality of operation buttons 1302, as well as an earpiece 1304 and a mouthpiece 1306.
In the liquid crystal display device, a polarizing plate is necessary, and thus the display screen is dark. However, the electrophoretic display panel 1308 does not require a polarizing plate. Therefore, the mobile phone 1300 can display a bright and easy-to-see screen.
In addition to the electronic devices described with reference to FIGS. 56 to 58, the electronic equipment includes a television monitor, an outdoor advertising board, a road sign, a viewfinder type, a monitor direct view type video tape recorder, and a car navigation device. , Pagers, electronic notebooks, calculators, word processors, workstations, videophones, POS terminals, devices equipped with touch panels, and the like. In addition, it goes without saying that the electrophoretic display panel of each embodiment and the electro-optical device including the same can be applied to these various electronic devices.

It is a disassembled perspective view which shows the mechanical structure of the electrophoretic display panel which concerns on 1st Embodiment. It is a fragmentary sectional view of the panel. It is a block diagram which shows the electrical constitution of the electrophoretic display device using the panel. It is sectional drawing which simplified and showed the structure of the division | segmentation cell of the panel. It is a graph which shows an example of the relationship between voltage application time and a gradation density. It is a block diagram of a data line driving circuit 140A of the same device. 4 is a timing chart of a scanning line driving circuit 130A and a data line driving circuit 140A. It is a block diagram of the PWM circuit 145 used for the data line drive circuit 140A. It is a timing chart which shows the signal waveform of a PWM signal. 6 is a timing chart showing an operation of a unit circuit Rj of the PWM circuit 145. 3 is a timing chart showing output data of an image signal processing circuit 300A. 5 is a timing chart of the electrophoretic display device in a reset operation. It is a timing chart of the electrophoretic display device in the writing operation. It is a timing chart for demonstrating the reset operation | movement which concerns on a 2nd aspect. It is a timing chart which shows operation in the case of resetting a plurality of horizontal lines simultaneously. It is a figure for demonstrating the horizontal line which should be rewritten. It is a block diagram which shows the electric constitution of the electrophoresis panel B which concerns on a 4th aspect. It is sectional drawing which simplified and showed the structure of the division cell. It is a block diagram of image processing circuit 301A. It is a block diagram of PWM circuit 145A. 3 is a timing chart showing output data of an image processing circuit 301A. It is a timing chart of the electrophoretic display device in the writing operation. It is a block diagram of the image signal processing circuit 300B. It is a timing chart of the output data of the image signal processing circuit 300B. It is a block diagram of PWM circuit 145B. It is a timing chart which shows operation of unit circuit Rj of PWM circuit 145B. It is a timing chart of the electrophoretic display device in the writing operation. It is a block diagram of the image processing circuit 301B. It is a block diagram of PWM circuit 145C. It is a figure which shows the relationship between the multiplex data Ddm and the data obtained by dividing | segmenting this. It is a timing chart which shows operation of unit circuit Rj of PWM circuit 145B. It is a timing chart of the electrophoretic display device in the writing operation. It is a block diagram of an image signal processing circuit 300C. 3 is a conceptual diagram showing a storage area of a first field memory 335 in association with pixels. FIG. It is a conceptual diagram which shows the memory area of the 2nd field 336 corresponding to a pixel. It is a block diagram of a scanning line driving circuit 130C. It is a timing chart of the scanning line driving circuit 130C. It is a timing chart of the scanning line driving circuit 130C. It is a block diagram of a data line driving circuit 140C. It is a truth table of selection unit Uj used for PWM circuit 144C. 6 is a timing chart of the data line signal Xj and the Y clock YCK when the reset timing signal Cr is inactive. It is a timing chart which shows the whole operation | movement of an electrophoretic display apparatus. It is a timing chart which shows the operation example of the electrophoretic display device in writing operation. It is a timing chart of the electrophoretic display device in the writing operation. It is a timing chart of the electrophoretic display device in the writing operation. It is a block diagram of the image processing circuit 301C. 3 is a conceptual diagram showing a storage area of a first field memory 335 in association with pixels. FIG. It is a block diagram of data line drive circuit 140D. It is a truth table of selection unit Uj used for PWM circuit 144C. 6 is a timing chart of the data line signal Xj and the first Y clock YCK1 when the reset timing signal Cr is inactive. It is a timing chart which shows the whole operation | movement of an electrophoretic display apparatus. 6 is a timing chart showing a writing operation of the electrophoretic display device. 6 is a timing chart showing a writing operation of the electrophoretic display device. 3 is a block diagram of a timer device 410. FIG. 5 is a timing chart showing the operation of the timer device 410. It is a general | schematic perspective view of the electronic book which is an example of an electronic device. It is a general | schematic perspective view of the personal computer which is an example of an electronic device. It is a general | schematic perspective view of the mobile telephone which is an example of an electronic device.

DESCRIPTION OF SYMBOLS 1 ... Dispersion system 2 ... Dispersion medium 3 ... Electrophoretic particle A ... Electrophoretic display panel 101 ... Scanning line 102 ... Data line 103 ... TFT (switching element)
104 ... Pixel electrode 201 ... Common electrode Va ... Applied voltage Vs ... Braking voltage Y1-Ym ... Scan line signal X1-Xn ... Data line signal 130A, 130C ... Scan line drive circuit (scan line drive unit) )
140A, 140B, 140C... Data line drive circuit (data line drive unit)

Claims (4)

A first electrode and a second electrode;
A dispersion system containing electrophoretic particles disposed between the first electrode and the second electrode;
A plurality of scan lines;
A plurality of data lines intersecting the plurality of scanning lines;
Provided corresponding to the intersection of the data line and the scanning line, the data line, the scanning line,
And a switching element electrically connected to the first electrode;
A method for driving an electrophoretic display device comprising:
A first step of applying a first voltage between the first electrode and the second electrode when switching a display;
A second step of applying a second voltage having a polarity opposite to that of the first electrode between the first electrode and the second electrode after the first step ;
After the second step, a third step of applying the same voltage to the first electrode as the second electrode ;
The method for driving an electrophoretic display device, wherein an application time of the second voltage in the second step is shorter than an application time of the first voltage in the first step. A first electrode and a second electrode;
A dispersion system containing electrophoretic particles disposed between the first electrode and the second electrode;
A plurality of scan lines;
A plurality of data lines intersecting the plurality of scanning lines;
A switching element provided corresponding to the intersection of the data line and the scanning line, and electrically connected to the data line, the scanning line, and the first electrode;
A control device for an electrophoretic display device comprising:
A first step of applying a first voltage between the first electrode and the second electrode when switching a display;
A second step of applying a second voltage having a polarity opposite to that of the first electrode between the first electrode and the second electrode after the first step;
After the second step, a third step of applying the same voltage as the second electrode to the first electrode;
Controlling the electrophoretic display device to perform
The control apparatus for an electrophoretic display device, wherein an application time of the second voltage in the second step is shorter than an application time of the first voltage in the first step. A first electrode and a second electrode;
A dispersion system containing electrophoretic particles disposed between the first electrode and the second electrode;
A plurality of scan lines;
A plurality of data lines intersecting the plurality of scanning lines;
A switching element provided corresponding to the intersection of the data line and the scanning line, and electrically connected to the data line, the scanning line, and the first electrode;
An electrophoretic display device comprising:
In switching the display, in the first step, a first voltage is applied between the first electrode and the second electrode,
In a second step after the first step, a second voltage having a polarity opposite to that of the first electrode is applied between the first electrode and the second electrode,
In a third step after the second step, the same voltage as the second electrode is applied to the first electrode;
The electrophoretic display device, wherein an application time of the second voltage in the second step is shorter than an application time of the first voltage in the first step.   An electronic apparatus comprising the electrophoretic display device according to claim 3 in a display portion.

Images