JP2013061595A - Method for driving electrophoretic display device, electrophoretic display device, electronic equipment and electronic clock - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for driving an electrophoretic display device for reducing local decrease in a contrast ratio and preventing an afterimage or flickers while maintaining a DC balance.SOLUTION: The driving method comprises: a first image display step (S12) of displaying a first image in a first color in a display unit by a partial drive system that comprises applying a voltage based on a drive pulse signal to a common electrode, applying a voltage to each of a plurality of pixel electrodes based on an inverted signal or a normal signal of a drive pulse signal to rewrite an image to be displayed in the display unit; a first image erase step (S14) of subsequently displaying the first image in a second color in the display unit by the partial drive system; a first preliminary display step (S22) of subsequently displaying the whole pixels in the display unit in an intermediate color; and a second preliminary display step (S24) of subsequently displaying the whole pixels of the display unit in the second color. The next image display step is carried out after the second preliminarily display step.

Description

  The present invention relates to an electrophoretic display device driving method, an electrophoretic display device, an electronic apparatus, an electronic timepiece, and the like.

  In recent years, a display panel having a memory property that can hold an image even when the power is turned off has been developed and used in an electronic timepiece or the like. As a display panel having a memory property, an EPD (Electrophoretic Display), that is, an electrophoretic display device, a memory-type liquid crystal display device, and the like are known.

  The electrophoretic display device has excellent advantages such as a wide viewing angle, high contrast ratio, flexibility, and low power consumption because it is a reflective display.

  On the other hand, as described in Patent Document 1, if the time average of the electric field applied between the electrodes is not substantially zero in the electrophoretic display device, the operation life of the device may be shortened. That is, in order to ensure the long-term reliability of the electrophoretic display device, it is necessary that the DC balance be taken, that is, the time average of the applied electric field is almost zero.

JP-T-2005-530201

  Here, the electrophoretic display device can display an image by a full drive method that draws the entire display unit or a partial drive method that can draw a part to be rewritten. The display unit of the electrophoretic display device includes, for example, a pixel electrode corresponding to an image pixel and a transparent common electrode, and a voltage is applied to each of these electrodes to move the electrophoretic element by the generated electric field. Update the image with.

  The partial drive method can update the display image in a short time. However, it is known that when a specific area is rewritten repeatedly by the partial drive method, the contrast ratio of the area decreases. Therefore, it is preferable from the viewpoint of long-term reliability that the entire display portion is rewritten uniformly.

  Therefore, the problem of a decrease in contrast ratio can be solved by always drawing the entire display portion by the entire surface driving method. However, since all the pixels are to be driven, it takes time to update the display image compared to the partial drive method.

  In order to shorten the update time by the full-surface drive method, for example, it is conceivable to shorten the drive time of a signal used for voltage application. However, in this case, an afterimage may occur because the driving of the signal is completed before the desired reflectance is reached.

  In addition, in order to achieve DC balance, if display of a desired image and reverse display are continuously executed by the full-surface driving method, the user may be recognized as flickering of the screen.

  The present invention has been made in view of such problems. According to some aspects of the present invention, there is provided a driving method of an electrophoretic display device that reduces a local contrast ratio reduction while maintaining DC balance and does not cause an afterimage or flicker.

(1) In the present invention, an electrophoretic element including electrophoretic particles is sandwiched between a pair of substrates, and a pixel capable of displaying a first color, a second color, and an intermediate color between the first color and the second color. A pixel electrode corresponding to the pixel is formed between one of the substrates and the electrophoretic element, and a plurality of the pixel electrodes are disposed between the other substrate and the electrophoretic element. A method for driving an electrophoretic display device in which a common electrode opposite to the first electrode is formed, wherein a voltage based on a driving pulse signal that repeats a first potential and a second potential is applied to the common electrode, and the plurality of pixels Applying a voltage based on an inverted signal of the driving pulse signal or a normal rotation signal to each of the electrodes, and moving the electrophoretic particles by an electric field generated between the pixel electrode and the common electrode, the display unit The image displayed on the screen An image display step for displaying the first image in the first color on the display unit by the minute drive method, and the first image on the display unit by the partial drive method after the image display step. An image erasing step for displaying in two colors, a first preliminary display step for displaying all pixels of the display portion in the intermediate color after the image erasing step, and an entire display portion after the first preliminary display step. A second preliminary display step of displaying pixels in the second color, and the next image display step is executed after the second preliminary display step.

(2) In the driving method of the electrophoretic display device, the first preliminary display step and the second preliminary display step may be configured such that all pixels of the display unit are displayed in the intermediate color or the second color by the partial drive method. The time for displaying and applying the voltage based on the drive pulse signal may be shorter than the time for applying the voltage based on the drive pulse signal in the image display step.

  According to these inventions, after executing the image display process and the image erasing process by the partial drive method, the first preliminary display process and the second preliminary display process for displaying all the pixels of the display unit in the intermediate color and the second color, respectively. Execute. In the partial driving method, a voltage based on a driving pulse signal that repeats a first potential and a second potential is applied to a common electrode, and an inverted signal of a driving pulse signal or a normal signal is applied to each of a plurality of pixel electrodes. An image displayed on the display unit is rewritten by applying a voltage and moving the electrophoretic particles by an electric field generated between the pixel electrode and the common electrode. In the partial drive method, it is possible to draw not only the entire display unit but also a part to be rewritten.

  In the image display step, the first image is displayed in the first color. In the image erasing step, the first image is displayed in the second color to be erased. Here, the first color is, for example, black, and the second color is, for example, white. The first image is an image displayed on a part of the display unit, and may be any one of letters, numbers, sentences, figures, symbols, patterns, or a combination thereof. The first image may change to a different character, number, sentence, figure, symbol, pattern, etc. each time it is displayed in the image display process. At this time, since each of the image display process and the image erasing process displays the first image in the first color and the second color, DC balance is achieved in these processes.

  Thereafter, the driving method of the electrophoretic display device according to these inventions executes the first preliminary display step and the second preliminary display step of rewriting all the pixels of the display unit. This makes it difficult for the local contrast ratio to decrease due to repeated display and erasure of only a part of the display unit corresponding to the first image.

  The local reduction in the contrast ratio is caused by repeating for a long time the application of an electric field to a partial region (hereinafter, a specific region) of the display unit. In other words, the number of times of driving a signal used for applying a voltage for a specific region and the number of times of driving for a region other than the specific region are greatly different with time.

  In the driving method of the electrophoretic display device of these inventions, the entire surface including the background of the first image is driven by the first preliminary display step and the second preliminary display step after executing the image display step and the image erasing step. . Therefore, it is possible to avoid a large difference in the number of times of driving between the first image (corresponding to the specific area) and the background of the first image. As a result, a local reduction in contrast ratio is unlikely to occur. In the first preliminary display step and the second preliminary display step, since the entire surface of the display unit is displayed in the first color and the second color, respectively, DC balance is achieved in these steps. In the above-described process, the desired image display and the reverse display are not continuously performed by the full-surface driving method. Therefore, no flickering occurs when the screen changes.

  Therefore, the driving method of the electrophoretic display device of these inventions does not cause a local contrast ratio reduction or flickering while maintaining DC balance. Therefore, long-term reliability can be ensured and display quality can be improved.

  Here, the time for executing the first preliminary display step and the second preliminary display step (specifically, the time for applying the voltage based on the drive pulse signal) is the time for executing the image display step (or image erasing step). May be shorter.

  In the first preliminary display step, the entire display unit is not displayed in the first color, but is displayed in an intermediate color between the first color and the second color. Therefore, the execution time of the first preliminary display step may be short. Since the second preliminary display process is only updated from the intermediate color to the second color display, the execution time may be short. Therefore, even if the first preliminary display step and the second preliminary display step are executed, there is no problem that it takes time to update the display image.

  The first preliminary display step and the second preliminary display step are preferably performed by the partial drive method in order to shorten the time required for display update, but may be the full drive method. In the case of the partial drive method, the problem of afterimages that can occur by shortening the drive time of the pulse signal by the full-surface drive method does not occur. Even in the case of the full drive method, the first preliminary display process and the second preliminary display process are performed following the image erasing process for displaying the entire surface in the second color. Therefore, in this case as well, the problem of afterimages that can be caused by shortening the drive time of the pulse signal does not occur.

  Furthermore, by executing the first preliminary display step and the second preliminary display step, the afterimage can be made inconspicuous even when there is an afterimage generated in the contour portion of the first image.

  In the driving method of the electrophoretic display device according to these inventions, the first preliminary display step and the second preliminary display step can erase even if an afterimage occurs in the contour portion, thereby improving the display quality.

(3) In the driving method of the electrophoretic display device, the third preliminary display step of displaying all the pixels of the display unit in the first color and the third preliminary display step are performed, and the display unit A fourth preliminary display step for displaying all the pixels in the second color, and when a predetermined condition is satisfied, after the second preliminary display step and before the next image display step is executed. In addition, the third preliminary display step and the fourth preliminary display step may be performed.

(4) In this method of driving an electrophoretic display device, the given condition may be that the image display step is executed a predetermined number of times.

  The driving method of the electrophoretic display device of these inventions includes a third preliminary display step for displaying the entire display portion in the first color and a fourth preliminary display step for displaying the entire display portion in the second color. As described above, the afterimage of the outline portion is not visually recognized in the first preliminary display step and the second preliminary display step, but there is a possibility that an afterimage that is not visually recognized by the user may be accumulated. Therefore, as time passes, color distortion such as “haze” may occur in some areas including the first image on the display unit of the electrophoretic display device. In the driving method of the electrophoretic display device according to these inventions, the entire display unit is displayed in the first color and the second color in the third preliminary display step and the fourth preliminary display step, respectively, and the entire display unit is refreshed. Such color disturbance can be prevented.

  However, if the third preliminary display process and the fourth preliminary display process are always executed, there is a possibility that it takes time to update the display image. Therefore, the third preliminary display step and the fourth preliminary display step may be performed on condition that the image display step is executed a predetermined number of times (for example, 10 times). At this time, it is possible to prevent color disturbance without taking time to update the display image. Here, the third preliminary display step and the fourth preliminary display step are preferably performed by a partial drive method in order to shorten the time required for display update, but may be a full drive method.

(5) The present invention may be an electrophoretic display device including a control unit that executes the method for driving the electrophoretic display device.

  According to the present invention, the control method is realized by the control unit included in the electrophoretic display device. For this reason, the electrophoretic display device of the present invention does not cause a local reduction in contrast ratio or afterimage while maintaining DC balance. Therefore, it is excellent in long-term reliability and display quality is improved.

(6) The present invention may be an electronic apparatus including the electrophoretic display device.

(7) The present invention may be an electronic timepiece including the electrophoretic display device.

  By using the electrophoretic display device, the electronic apparatus and the electronic timepiece according to these inventions do not cause a local contrast ratio decrease or afterimage while maintaining DC balance. Therefore, an electronic device and an electronic timepiece having excellent long-term reliability and good display quality can be realized.

1 is a block diagram of an electrophoretic display device according to a first embodiment. FIG. 3 is a diagram illustrating a configuration example of a pixel of the electrophoretic display device according to the first embodiment. FIG. 3A illustrates a configuration example of an electrophoretic element. 3B and 3C are explanatory diagrams of the operation of the electrophoretic element. FIG. 4A to FIG. 4B are waveform diagrams of the partial drive method and examples of reflectance. FIG. 5A to FIG. 5D are diagrams for explaining a local decrease in contrast ratio. FIG. 6A to FIG. 6B are waveform diagrams of the full-surface driving method and examples of reflectance. FIGS. 7A to 7E are diagrams for explaining afterimage generation in the full-surface driving method. 8A to 8H are display examples of the first embodiment. The flowchart of 1st Embodiment. 10A to 10F are display examples of the second embodiment. The flowchart of 2nd Embodiment. 12A to 12C are diagrams illustrating display blur. FIGS. 13A to 13F are display examples of the third embodiment. The flowchart of 3rd Embodiment. FIG. 15A to FIG. 15H are display examples of the fourth embodiment. The flowchart of 4th Embodiment. The wave form diagram of 4th Embodiment. 18A to 18F are display examples of the fifth embodiment. The flowchart of 5th Embodiment. The flowchart of the modification of 5th Embodiment. The block diagram of the electronic device of an application example. FIG. 22A is a diagram of an electronic timepiece that is an example of an electronic device, and FIG. 22B is a diagram of electronic paper that is an example of an electronic device.

1. First Embodiment A first embodiment of the present invention will be described with reference to FIGS. The electrophoretic display device according to the first embodiment is capable of displaying various images such as letters, numbers, photographs, patterns, and illustrations.

1.1. Configuration of Electrophoretic Display Device FIG. 1 is a diagram illustrating a configuration of an active matrix type electrophoretic display device of the present embodiment.

  The electrophoretic display device 10 includes a display control circuit 60 and a display unit 3. The display control circuit 60 is a control unit that controls the display unit 3, and includes a scanning line driving circuit 61, a data line driving circuit 62, a controller 63, a common power supply modulation circuit 64, and a storage unit 160.

  The scanning line driving circuit 61, the data line driving circuit 62, the common power supply modulation circuit 64, and the storage unit 160 are each connected to the controller 63. The controller 63 comprehensively controls these based on an input signal (not shown) such as a time signal, for example.

  The storage unit 160 may include, for example, a VRAM and a nonvolatile memory such as a flash memory (not shown). The VRAM stores image data to be displayed on the display unit 3. The VRAM is divided into a plurality of banks, and each may function as an individual VRAM. The non-volatile memory stores data of elements constituting the data stored in the VRAM (for example, part data and background data). In addition, the storage unit 160 may include, for example, SRAM, DRAM, and the like.

  The display unit 3 is formed with a plurality of scanning lines 66 extending from the scanning line driving circuit 61 and a plurality of data lines 68 extending from the data line driving circuit 62, and a plurality of pixels corresponding to these intersecting positions. 40 is provided.

  The scanning line driving circuit 61 is connected to each pixel 40 by m scanning lines 66 (Y1, Y2,..., Ym). The scanning line driving circuit 61 specifies the on-timing of the driving TFT 48 (see FIG. 2) provided in the pixel 40 by sequentially selecting the scanning lines 66 from the first row to the m-th row under the control of the controller 63. A selection signal is supplied.

  The data line driving circuit 62 is connected to each pixel 40 by n data lines 68 (X1, X2,..., Xn). The data line driving circuit 62 supplies an image signal defining 1-bit image data corresponding to each of the pixels 40 to the pixels 40 under the control of the controller 63. In this embodiment, when the pixel data “0” is defined, the low-level image signal is supplied to the pixel 40, and when the pixel data “1” is defined, the high-level image signal is supplied to the pixel 40. 40.

  The display unit 3 also includes a low-potential power line 49 (Vss), a high-potential power line 50 (Vdd), a common electrode line 55 (Vcom), and a first pulse signal line 91 (S1) extending from the common power modulation circuit 64. ), A second pulse signal line 92 (S 2) is provided, and each wiring is connected to the pixel 40. The common power supply modulation circuit 64 generates various signals to be supplied to each of the wirings according to the control of the controller 63, and performs electrical connection and disconnection (high impedance, Hi-Z) of these wirings.

1.2. Circuit Configuration of Pixel Part FIG. 2 is a circuit configuration diagram of the pixel 40 of FIG. In addition, the same number is attached | subjected to the same wiring as FIG. 1, and description is abbreviate | omitted. Further, the description of the common electrode wiring 55 common to all pixels is omitted.

  The pixel 40 is provided with a driving TFT (Thin Film Transistor) 48, a latch circuit 70, and a switch circuit 80. The pixel 40 has an SRAM (Static Random Access Memory) type configuration in which an image signal is held as a potential by a latch circuit 70.

  The driving TFT 48 is a pixel switching element made of an N-MOS transistor. The gate terminal of the driving TFT 48 is connected to the scanning line 66, the source terminal is connected to the data line 68, and the drain terminal is connected to the data input terminal of the latch circuit 70. The latch circuit 70 includes a transfer inverter 70t and a feedback inverter 70f. The transfer inverter 70t and the feedback inverter 70f are supplied with the power supply voltage from the low potential power supply line 49 (Vss) and the high potential power supply line 50 (Vdd).

  The switch circuit 80 includes transmission gates TG1 and TG2, and outputs a signal to the pixel electrode 35 (see FIGS. 3B and 3C) according to the level of the pixel data stored in the latch circuit 70. . Note that Va means a potential (signal) supplied to the pixel electrode of one pixel 40.

  When pixel data “1” (high-level image signal) is stored in the latch circuit 70 and the transmission gate TG1 is turned on, the switch circuit 80 supplies the signal S1 as Va. On the other hand, when pixel data “0” (low-level image signal) is stored in the latch circuit 70 and the transmission gate TG2 is turned on, the switch circuit 80 supplies the signal S2 as Va. With such a circuit configuration, the display control circuit 60 can control the potential (signal) supplied to the pixel electrode of each pixel 40.

1.3. Display Method The electrophoretic display device 10 of the present embodiment is a two-particle microcapsule type electrophoresis method. If the dispersion is colorless and transparent, and the electrophoretic particles are white or black, at least two colors can be displayed with two colors of white or black as basic colors. Here, it is assumed that the electrophoretic display device 10 can display black and white as basic colors. Then, displaying a pixel displaying black in white, or displaying a pixel displaying white in black is expressed as inversion.

  FIG. 3A is a diagram showing a configuration of the electrophoretic element 132 of the present embodiment. The electrophoretic element 132 is sandwiched between the element substrate 130 and the counter substrate 131 (see FIGS. 3B and 3C). The electrophoretic element 132 is configured by arranging a plurality of microcapsules 120. The microcapsule 120 encloses, for example, a colorless and transparent dispersion, a plurality of white electrophoretic particles (white particles 127), and a plurality of black electrophoretic particles (black particles 126). In the present embodiment, for example, it is assumed that the white particles 127 are negatively charged and the black particles 126 are positively charged.

  FIG. 3B is a partial cross-sectional view of the display unit 3 of the electrophoretic display device 10. The element substrate 130 and the counter substrate 131 sandwich the electrophoretic element 132 in which the microcapsules 120 are arranged. The display unit 3 (see FIG. 1) includes a drive electrode layer 350 in which a plurality of pixel electrodes 35 are formed on the electrophoretic element 132 side of the element substrate 130. In FIG. 3B, a pixel electrode 35A and a pixel electrode 35B are shown as the pixel electrode 35. The pixel electrode 35 can supply a potential to each pixel (for example, Va, Vb). Here, a pixel having the pixel electrode 35A is referred to as a pixel 40A, and a pixel having the pixel electrode 35B is referred to as a pixel 40B. The pixel 40A and the pixel 40B are two pixels corresponding to the pixel 40 (see FIGS. 1 and 2).

  On the other hand, the counter substrate 131 is a transparent substrate, and an image is displayed on the counter substrate 131 side in the display unit 3. The display unit 3 includes a common electrode layer 370 in which a common electrode 37 having a planar shape is formed on the electrophoretic element 132 side of the counter substrate 131. The common electrode 37 is a transparent electrode. Unlike the pixel electrode 35, the common electrode 37 is an electrode common to all pixels, and is supplied with the potential Vcom.

  The electrophoretic element 132 is disposed on the electrophoretic display layer 360 provided between the common electrode layer 370 and the drive electrode layer 350, and the electrophoretic display layer 360 serves as a display region. A desired display color can be displayed for each pixel according to the potential difference between the common electrode 37 and the pixel electrode (for example, 35A, 35B).

  In FIG. 3B, the potential Vcom on the common electrode side is higher than the potential Va of the pixel electrode of the pixel 40A. At this time, the negatively charged white particles 127 are attracted to the common electrode 37 side, and the positively charged black particles 126 are attracted to the pixel electrode 35A side, so that the pixel 40A is visually recognized as displaying white.

  In FIG. 3C, the potential Vcom on the common electrode side is lower than the potential Va of the pixel electrode of the pixel 40A. At this time, on the contrary, the positively charged black particles 126 are attracted to the common electrode 37 side, and the negatively charged white particles 127 are attracted to the pixel electrode 35A side, so that it is visually recognized that the pixel 40A displays black. Is done. Note that the structure in FIG. 3C is similar to that in FIG. 3 (B) and 3 (C), Va, Vb, and Vcom are described as fixed potentials. However, in reality, Va, Vb, and Vcom change with time. Hereinafter, a signal for applying the potentials Va, Vb, and Vcom is referred to as a pulse signal. In particular, a pulse signal to the common electrode is called a drive pulse signal.

  Here, it is assumed that the state is changed to the state shown in FIG. 3C after FIG. At this time, the pixel 40A is displayed white and then black, and the direction of the applied electric field changes in the opposite direction. For the pixel 40A, the applied electric field is symmetric and DC balanced. On the other hand, only the white color of the pixel 40B is displayed, the applied electric field is not symmetrical, and the DC balance is not achieved. In order to ensure long-term reliability of the electrophoretic display device, it is necessary to perform reverse display like the pixel 40A of this example.

1.4. Driving Method First, referring to FIGS. 4A to 7E, the driving method of the pulse signal when the control unit (corresponding to the display control circuit 60 in FIG. 1) performs control to display an image on the display unit. I will explain.

1.4.1. Partial Drive Method FIG. 4A is a waveform diagram of the partial drive method. In the electrophoretic display device, in order to increase the response speed, there is a case in which a part to be rewritten is drawn instead of drawing the entire display unit. With the partial drive method, it is possible to draw a part of the object to be rewritten. Note that Va, Vb, and Vcom in FIG. 4A are the same as those in FIGS. 3B to 3C, and Va, Vb, and Vcom are high level (VH), low level (VL), or high. An impedance state (Hi-Z) can be taken.

  Vcom in FIG. 4A indicates an example of a driving pulse signal to the common electrode. Here, Vcom is a second potential having a short pulse width T2 (hereinafter simply referred to as T2) after a pulse in which the first potential is applied to the common electrode with a certain pulse width T1 (hereinafter simply referred to as T1). Followed by a pulse (reverse potential drive pulse) that applies to the common electrode and is repeated. However, as shown in FIG. 4A, the first potential is exceptionally applied to the common electrode immediately before the drive is stopped, and the process ends. The drive time at the time of partial rewriting can be further shortened by the reverse potential drive pulse having a short pulse width. Here, when displaying white, the first potential is VH (second potential is VL), and when displaying black, the first potential is VL (second potential is VH). . For example, T2 may be as short as 1% to 15% of T1.

  In this example, the pulse signal that applies the potential Va applied to the pixel electrode of the pixel 40A is an inverted signal of the drive pulse signal. Further, the pulse signal for applying the potential Vb applied to the pixel electrode of the pixel 40B is the same signal (normal rotation signal) as the drive pulse signal. The pixel 40A and the pixel 40B are, for example, the two pixels shown in FIG. The pixel 40A is rewritten from black to white during the period indicated as “white display” in FIG. 4A and from white to black during the period indicated as “black display”. On the other hand, the pixel 40B continues black display without being rewritten because no electric field is generated between the common electrode and the pixel electrode.

  FIG. 4B is a diagram illustrating a change in color (reflectance) of the pixel 40A and the pixel 40B according to the example of FIG. First, the pixel 40A will be described. It is assumed that the pixel 40A is initially displayed in black. In the section corresponding to T1 of “white display”, the potential of the pixel electrode is VL and the potential of the common electrode is VH. However, in the section corresponding to T2 of “white display”, the potential of the pixel electrode is VH and the potential of the common electrode is VL. However, since T1> T2, the pixel 40A is displayed in white at the end of the “white display” period. The pixel 40A is displayed in black at the end of the “black display” period in which the polarity of Vcom is inverted.

  On the other hand, since the same signal as Vcom is always supplied to the pixel electrode, the pixel 40B does not cause a potential difference and continues the black display from the beginning. Thus, in the partial drive method, only the pixel to be changed can be driven, and the response speed in image rewriting can be increased. In particular, by using a reverse potential drive pulse with a short pulse width, the drive time during partial rewriting can be shortened.

  Note that, since it is suitable for drawing a part to be rewritten, such a pulse signal driving method is called a partial driving method. However, the partial drive method does not limit the rewrite target to some pixels of the display unit. Therefore, it is possible to draw all pixels of the display portion by a partial drive method.

1.4.2. Problems with Partial Drive Method FIGS. 5A to 5D are diagrams for explaining a local reduction in contrast ratio when a partial region is rewritten with the partial drive method. 5A to 5C, time display (10:05 or 10:06) is performed on the display unit 3, and the region 51 including a minute digit is rewritten by the partial drive method. .

  In FIG. 5A, time 10:05 is displayed. Then, when the time changes to 10:06, as shown in FIG. 5B, the one-digit digit “5” in the region 51 is highlighted (displayed in white) and erased. Next, as shown in FIG. 5C, black “6” with white background is displayed in a normal rotation. At this time, the DC balance is obtained between FIG. 5A and FIG. 5B, and the update is performed in the range of the region 51 which is a part of the display unit 3, so that the time required for the update display can be shortened. As shown in FIGS. 5 (A) to 5 (C), the time display is updated by the partial drive method, thereby realizing an electrophoretic display device capable of maintaining DC reliability, ensuring long-term reliability, and enabling quick update display. it can.

  However, if such updated display is continued for a long period of time, a local contrast ratio may be lowered. This state is shown in FIG. In FIG. 5D, the entire surface of the display unit 3 is displayed in white, but the contrast ratio is lowered in the region 51. Therefore, the white color of the region 51 is different from other regions (for example, the region 52).

  Here, the local reduction in the contrast ratio is caused by repeatedly applying an electric field to a partial region 51 of the display unit 3 for a long time. That is, the number of times of driving the signal used for applying the voltage for the region 51 and the number of times of driving for the region other than the region 51 (for example, the region 52) are greatly different with time. The local reduction in contrast ratio as shown in FIG. 5D reduces the display quality of the display unit 3.

1.4.3. Full Drive Method FIG. 6A is a waveform diagram of the full drive method. In the electrophoretic display device, an image can be displayed by a full-surface driving method in which the entire display unit is drawn. At this time, since the application of an electric field to a partial region of the display unit is not repeated for a long time, unlike the partial driving method, a local contrast ratio is not lowered. Note that Va, Vb, Vcom, VH, and VL in FIG. 6A are the same as those in FIGS. 3A to 4B, and a description thereof is omitted.

  FIG. 6A shows a waveform diagram in the case where the pixel 40A is changed from black to white and the pixel 40B is changed from white to black by the full-surface driving method. In FIG. 6A, while the display color changes, Va remains at the low level (VL) and Vb remains at the high level (VH). Vcom repeats VL and VH for the same amount of time. That is, the pulse width T3 (hereinafter simply referred to as T3) and the pulse width T4 (hereinafter simply referred to as T4) in FIG.

  FIG. 6B is a diagram illustrating a change in color (reflectance) of the pixel 40A and the pixel 40B according to the example of FIG. The pixel 40A is initially displayed in black. In the section corresponding to T3 in FIG. 6B, the potential of the pixel electrode is VL and the potential of the common electrode is VH. In the section corresponding to T4 in FIG. 6B, no potential difference occurs between the pixel electrode and the common electrode, so that the color is maintained. Finally, the pixel 40A changes from black to white.

  On the other hand, the pixel 40B is initially displayed in white. In the section corresponding to T3 in FIG. 6B, no color difference is generated between the pixel electrode and the common electrode, so that the color is maintained. In the section corresponding to T4 in FIG. 6B, the potential of the pixel electrode is VH and the potential of the common electrode is VL. Finally, the pixel 40B changes from white to black.

  Here, in the full-surface driving method, a potential of VL or VH is applied to the pixel electrodes of all the pixels of the display unit 3. And since it does not repeat applying an electric field only to the partial area | region of a display part for a long time, the fall of a local contrast ratio does not arise.

  Note that in the full-surface driving method, all pixels in the display unit are objects to be drawn, and only some pixels in the display unit cannot be rewritten. As the name suggests, all pixels on the display unit are drawn.

1.4.4. Problems in the full drive system FIGS. 7A to 7E are diagrams for explaining the occurrence of an afterimage in the full drive system. First, as shown in FIG. 7A, the display unit 3 is divided into four regions (upper left, upper right, lower left, lower right), and the upper left region and upper right region are particularly referred to as region X and region Y, respectively. To. Here, it is assumed that there are adjacent pixels 40A and 40B as shown in FIG.

  FIG. 7B to FIG. 7D show a state in which an image is updated by the full drive method. First, in FIG. 7B, the left half of the display unit 3 including the region X is displayed in black, and the right half including the region Y is displayed in white. FIG. 7B is an original image before update.

  Here, it is assumed that the display image is updated, and the updated image is an image in which the upper half including the region X and the region Y is black. At this time, in order to achieve DC balance, first, reverse display is performed as shown in FIG. That is, as shown in FIG. 7C, the region X and the region Y are displayed in white.

  Thereafter, an image in which the upper half including the region X and the region Y is black as shown in FIG. 7D is displayed, but the black of the region Y and the black of the region X are different. In the example of FIG. 7D, the black color in the region Y has a higher reflectance than the black color in the region X. Due to such a difference in reflectance, an afterimage may occur when an image is updated by a full-surface driving method.

FIG. 7E compares the change in reflectance of the pixel 40A included in the region X and the pixel 40B included in the region Y. The interval _{T B} is 7 in FIG. 7 (E) (B), the interval _{T C} in FIG. 7 (C), the interval _{T D} corresponds to FIG. 7 (D). First, the pixel 40A is black at first (section T _B ), and then changes to white and black (section T _C , T _D ). This change is expressed as (black, white, black). Then, the change of the pixel 40B can be expressed as (white, white, black).

Here, the reflectivity _R C (= _{R 1} in the case of sufficiently long operating time of the pulse signal on the entire surface drive method also pixel 40A also pixel 40B in _{(T EX} min only when extending the _{T D)} FIG. 7 (E) ) To converge. Therefore, there is no difference in reflectivity, and no afterimage is generated. However, in actuality, there is no extension of T _EX in order to shorten the display image update time. Then, (black, white, black) and changing the pixel 40A in reflectance R _A, (white, white, black) because the change pixel 40B becomes the reflectance R _B, and a difference in reflectivity caused afterimage Will occur.

  Therefore, when the full drive method is used instead of the partial drive method, the local contrast ratio does not decrease, but an afterimage may occur as another problem. Therefore, there is a need for a method for driving an electrophoretic display device that does not cause a problem of local contrast ratio reduction or afterimage.

1.5. Display Example of this Embodiment FIGS. 8A to 8H show display examples of this embodiment. 8A to 8H each represent a display image of the display unit 3, and the right diagram represents pixels driven to display the display unit 3 in dark gray. This represents the drive pixel 13. Below the drive pixel 13, there is a distinction between the full drive method and the partial drive method and whether the pixel represented by the dark gray of the drive pixel 13 is displayed in black or white. Has been.

  Further, the process names in FIGS. 8A to 8H correspond to the process names in the flowcharts described later. The numbers enclosed in parentheses after the steps represent the order of execution in order to distinguish the steps having the same name.

  Here, the control unit of the electrophoretic display device of the present embodiment performs control to update the image on the display unit from the already displayed original image to the next new image. That is, the control for deleting the original image and displaying the new image is executed.

  Control for deleting the original image and control for displaying the new image are executed in a predetermined order. Each stage of executing control related to image update is called a process. For example, the stage in which the control unit executes the first image display control is expressed as a first image display process. In the following, the execution of the corresponding control by the control unit in each process is simply expressed as “execute the process”. For example, executing the first image display control by the control unit in the first image display process is simply expressed as executing the first image display process.

  FIG. 8A shows the display image of the display unit 3 when the first image display step (1) is executed, and the drive pixel 13 for that purpose. In the first image display step (1), the time display 10:05 (corresponding to the first image) is displayed in black (corresponding to the first color) on the display unit 3 by the partial drive method. It is assumed that the entire display unit 3 is in a white state before the execution of the first image display step (1).

  FIG. 8B shows the display image of the display unit 3 when the first image erasing step (1) is executed, and the drive pixel 13 for that purpose. In the first image erasing step (1), a portion other than the time display 10:05 (corresponding to the background of the first image) is displayed in black (corresponding to the first color) on the display unit 3 by the partial driving method. At this time, the entire display unit 3 is in a black state.

  FIG. 8C shows the display image of the display unit 3 when the second image display step (1) is executed and the drive pixel 13 for that purpose. In the second image display step (1), the portion other than the time display 10:06 (corresponding to the background of the second image) is displayed in white (corresponding to the second color) on the display unit 3 by the partial drive method. At this time, the time display 10:06 is displayed in black on the display unit 3.

  FIG. 8D shows the display image of the display unit 3 when the second image erasing step (1) is executed, and the drive pixel 13 for that purpose. In the second image erasing step (1), the time display 10:06 (corresponding to the second image) is displayed in white (corresponding to the second color) by the partial drive method. At this time, the entire surface of the display unit 3 is white.

  FIG. 8E shows the display image on the display unit 3 and the drive pixel 13 for the display image when the first image display step (2) is executed again after the second image erasing step (1). In the first image display step (2), the time display 10:07 (corresponding to the first image) is displayed in black (corresponding to the first color) on the display unit 3 by the partial drive method.

  Hereinafter, FIGS. 8F to 8H are FIGS. 8B to 8D, respectively, in which the first image is time display 10:07 and the second image is time display 10:08. Therefore, detailed description is omitted. In the example of FIGS. 8A to 8H, the time display changes every minute, and each process is executed in response to the change. For example, one minute after the time display 10:05 is displayed (FIG. 8 (A)), the entire display portion 3 is in a black state (FIG. 8 (B)), and then the time display 10:06 is displayed. Is displayed (FIG. 8C).

  These steps (first image display step, first image erasing step, second image display step, second image erasing step) are all partial drive methods, and the display image update processing time is shortened by the full surface drive method. There is no afterimage that occurs when

  Here, when the driving pixels 13 in the first image display step (1) and the first image erasing step (1) are combined, the pixels of the entire display portion are changed to black (FIG. 8A to FIG. 8). A) of B). On the other hand, when the driving pixels 13 in the second image display step (1) and the second image erasing step (1) are combined, the pixels of the entire display portion are changed to white (FIGS. 8C to 8D). B1). Therefore, DC balance is taken in these four steps (a1 and b1 in FIGS. 8A to 8D). In addition, DC balance is similarly taken about a2 and b2 of FIG.8 (E)-FIG.8 (H).

  Here, in the driving method of the electrophoretic display device of the present embodiment, there is no problem of local reduction in contrast ratio that may occur in the partial driving method. In other words, since the pixels of the entire display unit are changed to black (first image display step and first image erasing step) or white (second image display step and second image erasing step), This is because the electric field is applied uniformly.

  The local reduction in the contrast ratio is caused by repeating for a long time the application of an electric field to a partial region (hereinafter, a specific region) of the display unit. In other words, the number of times of driving a signal used for applying a voltage for a specific region and the number of times of driving for a region other than the specific region are greatly different with time. In the driving method of the electrophoretic display device of the present invention, such a specific region does not occur, and therefore a local contrast ratio does not decrease.

  Therefore, in the driving method of the electrophoretic display device of the present embodiment, the local contrast ratio is not lowered and the afterimage is not generated while the DC balance is achieved. Therefore, long-term reliability can be ensured and display quality is improved.

1.6. Flowchart The control process performed by the control unit of the electrophoretic display device of this embodiment is as shown in the flowchart of FIG. As shown in FIG. 9, the first image display step (S2) for displaying the first image (for example, time display with an odd minute digit) in the first color (for example, black) is executed. Then, a first image erasing step (S4) is performed in which the background of the first image is displayed in the first color to make the entire display unit the first color. Subsequently, a second image display step (S6) is performed in which the background of the second image (for example, time display with an even minute digit) is displayed in the second color (for example, white). Then, a second image erasing step (S8) is performed in which the second image is displayed in the second color to make the entire display unit the second color. Then, after the second image erasing step (S8), the process returns to the first image display step (S2).

  Here, in the electrophoretic display device of the present embodiment, since DC balance is achieved in these four steps, the display image is updated (displayed and erased) an even number of times, such as time display. Is suitable.

2. Second Embodiment A second embodiment of the present invention will be described with reference to FIGS. In addition, the same code | symbol is attached | subjected about the same element as FIGS. 1-9, and description is abbreviate | omitted.

2.1. Pattern boundary line In the first embodiment, the first image (or the second image) is different from the background of the first image (or the background of the second image) in order to prevent a local contrast ratio from decreasing. Drive in two steps. For example, the first image (or the second image) is displayed when a display change corresponding to the expected pixel size does not occur due to the property that the last driven particle among the electrophoretic particles described later spreads. ) In the contour portion (hereinafter referred to as pattern boundary line) may be visually recognized.

  For example, when the first image display process continues for a long time, there is a possibility that the black color extends beyond the outline of the first image to a part of the background. In the subsequent first image erasing step, the background of the first image is displayed in black. However, the pattern boundary may be visible because the reflectivity when a part of the background with black already spread is displayed in black and the reflectivity when the other (white) background is displayed in black. There is. In the second embodiment, even if such a pattern boundary line occurs, it can be made inconspicuous, so that display quality can be improved.

2.2. Display Example of Present Embodiment FIGS. 10A to 10F show display examples of the present embodiment. The process names in FIGS. 10A to 10F correspond to the process names in the flowcharts described later. In addition, the same code | symbol is attached | subjected to the same element as FIG. 8 (A)-FIG. 8 (H), and description is abbreviate | omitted. In addition, only items different from those in FIGS. 8A to 8H will be described in order to avoid redundant description.

  In the present embodiment, a first single color display step of displaying all the pixels of the display unit 3 in black (corresponding to the first color) as shown in FIG. 10C, and the display unit 3 as shown in FIG. And a second single color display step for displaying all the pixels in white (corresponding to the second color). The first image display process in FIG. 10A, the first image deletion process in FIG. 10B, the second image display process in FIG. 10D, and the second image deletion process in FIG. 8A, the first image display step (1), the first image erasing step (1) in FIG. 8B, the second image display step (1) in FIG. 8C, and FIG. Since the display image of the display unit 3 and the drive pixel 13 are the same as the second image erasing step (1) of D), the description is omitted.

  In the first single color display process of FIG. 10C, after the first image erasing process of FIG. 10B, all pixels of the display portion 3 are made black by the partial drive method. At this time, the pattern boundary line that may occur in the first image erasing process of FIG. 10B can be made inconspicuous.

  Further, in the second single color display process of FIG. 10F, after the second image erasing process of FIG. At this time, the pattern boundary line that may occur in the second image erasing step of FIG.

  In the driving method of the electrophoretic display device according to the present embodiment, a boundary line (pattern boundary) generated in the outline portion of the first image or the second image by including the first single color display step and the second single color display step. Even when there is a line), the pattern boundary line can be made inconspicuous. In the electrophoretic display device driving method of the present invention, DC balance is achieved in the first single color display step and the second single color display step (c1 in FIG. 10C and FIG. 10F). D1).

2.3. Flowchart The control process performed by the control unit of the electrophoretic display device of this embodiment is as shown in the flowchart of FIG. In addition, the same step (process) as FIG. 9 is attached | subjected with the same code | symbol, and detailed description is abbreviate | omitted.

  In the present embodiment, the first image display step (S2) for displaying the first image in the first color is executed. Then, a first image erasing step (S4) is performed in which the background of the first image is displayed in the first color to make the entire display unit the first color. At this time, a pattern boundary line may be generated in the first image erasing process. Therefore, in order to make the pattern boundary line inconspicuous, a first single color display process is performed to make the entire display unit the first color (S5). In this embodiment, the entire display unit is set to the first color by the partial drive method.

  Thereafter, a second image display step (S6) for displaying the background of the second image in the second color is executed. Then, a second image erasing step (S8) is performed in which the second image is displayed in the second color to make the entire display unit the second color. At this time, there is a possibility that a pattern boundary line is generated in the second image erasing step. Therefore, in order to make the pattern boundary line inconspicuous, a second single color display process is performed to make the entire display unit the second color (S9). In the present embodiment, the entire display unit is set to the second color by the partial drive method. Then, after the second single color display step (S9), the process returns to the first image display step (S2).

  Here, in the electrophoretic display device of the present embodiment, since DC balance is achieved in these six steps, the display image is updated (displayed and erased) an even number of times, such as time display. Is suitable.

3. Third Embodiment A third embodiment of the present invention will be described with reference to FIGS. In addition, the same code | symbol is attached | subjected about the same element as FIGS. 1-11, and description is abbreviate | omitted.

3.1. Display blur In the first embodiment and the second embodiment, when the entire display unit is white, a step of displaying the first image in black (first image display step), and when the entire display unit is black And a step of displaying the background of the second image in white (second image display step). Here, the electrophoretic display device has a property that the color displayed lastly spreads when the display is performed by the partial drive method. In the first and second embodiments, black (first image) spreads in the first image display step, and white (background of the second image) spreads in the second image display step. At this time, even if the first image and the second image are the same, the size and color may appear different depending on whether the first image is displayed in the first image display step or the second image display step. May end up.

  This display blur will be described with reference to FIGS. FIG. 12A shows a checkered display when there is no display blur. Ideally, the image is displayed as shown in FIG. 12A in both the first image display process and the second image display process. However, the first image display step corresponds to the case where black is displayed in a single white color as shown in FIG. 12B, and the black display appears blurred and large. On the other hand, the second image display process corresponds to the case where white display is performed on a single black color as shown in FIG. That is, the black display looks small. Therefore, in the first embodiment and the second embodiment, there is a possibility that different impressions are displayed in the first image display step and the second image display step.

  In the present embodiment, it is possible to avoid changes in the size and color of the display image.

3.2. Display Example of this Embodiment FIGS. 13A to 13F show display examples of this embodiment. The process names in FIGS. 13A to 13F correspond to the process names in the flowchart described later. The numbers enclosed in parentheses after the steps represent the order of execution in order to distinguish the steps having the same name. Also, the same elements as those in FIGS. 8A to 8H are denoted by the same reference numerals, and description thereof is omitted. In addition, only items different from those in FIGS. 8A to 8H will be described in order to avoid redundant description.

  The present embodiment includes a display initialization step of displaying all the pixels of the display unit 3 in white (corresponding to the second color) as shown in FIGS. 13C and 13F. Before the first image display step of displaying the first image in black (corresponding to the first color), it is possible to avoid changing the size and hue by setting all the pixels to white.

  In this embodiment, white display is not performed after the entire surface is black. That is, the second image display process (see FIG. 8C, FIG. 8G, and FIG. 10D) included in the first embodiment and the second embodiment and the second image erasing process (FIG. 8). (D), FIG. 8 (H), and FIG. 10 (E)) are not included.

  The first image display step (1) of FIG. 13A and the first image deletion step (1) of FIG. 13B are respectively the first image display step (1) and FIG. Since the display image of the display unit 3 and the drive pixel 13 are the same as the first image erasing step (1) of B), the description thereof will be omitted.

  Through the display initialization process of FIG. 13C, all the pixels in the display portion 3 become white. Therefore, the next first image (time display 10:06) is then displayed in black by the first image display step in FIG. Each step of FIGS. 13E to 13F is the same as FIGS. 13B to 13C, and thus description thereof is omitted.

  In the driving method of the electrophoretic display device of the present embodiment, all the pixels of the display unit 3 are always white in the display initialization process. Therefore, the first image is always displayed in black from the state where all the pixels are white. Therefore, the problem that the hue changes does not occur.

  In the driving method of the electrophoretic display device of the present invention, for example, when the driving pixels 13 in the first image display step (1) and the first image erasing step (1) are combined, the pixels of the entire display unit are changed to black. (A1 in FIGS. 13A to 13B). In the display initialization step (1), the pixels of the entire display portion are changed to white (e1 in FIG. 13C). Therefore, DC balance is taken in these three steps. Note that DC balance is similarly achieved in the first image display step (2), the first image erasing step (2), and the display initialization step (2) (FIGS. 13D to 13F). A2 and e2).

3.3. Flowchart The control process performed by the control unit of the electrophoretic display device of this embodiment is as shown in the flowchart of FIG. The same steps as those in FIG. 9 are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the present embodiment, the first image display step (S2) for displaying the first image in the first color is executed. Then, a first image erasing step (S4) is performed in which the background of the first image is displayed in the first color to make the entire display unit the first color. And the display initialization process (S10) which makes all the pixels of the display part 3 white by a partial drive system is performed. Then, after the display initialization step (S10), the process returns to the first image display step (S2).

  Here, in the electrophoretic display device of this embodiment, since DC balance is achieved in these three steps, unlike the first embodiment and the second embodiment, a scheduled display image update (display and display) is performed. (Erase) can be applied evenly or oddly.

4). Fourth Embodiment A fourth embodiment of the present invention will be described with reference to FIGS. In addition, the same code | symbol is attached | subjected about the same element as FIGS. 1-14, and description is abbreviate | omitted.

4.1. Display flicker In order to achieve DC balance, display of a desired image and reverse display may be executed continuously by a full-surface driving method. At this time, the user may feel flickering on the screen. In the driving method of the electrophoretic display device of the present embodiment, display of a desired image and reverse display are not continuously performed in all steps, and such flickering of the screen can be suppressed. .

4.2. Display Example of this Embodiment FIGS. 15A to 15H show display examples of this embodiment. The process names in FIGS. 15A to 15H correspond to the process names in the flowchart described later. The numbers enclosed in parentheses after the steps represent the order of execution in order to distinguish the steps having the same name.

  FIG. 15A shows the display image of the display unit 3 when the image display step (1) is executed, and the drive pixel 13 therefor. In the image display step (1), the time display 10:05 (corresponding to the first image) is displayed in black (corresponding to the first color) on the display unit 3 by the partial drive method. It is assumed that the entire display unit 3 is white before the execution of the image display step (1).

  FIG. 15B shows the display image of the display unit 3 when the image erasing step (1) is executed, and the drive pixel 13 for that purpose. In the image erasing step (1), the time display 10:05 (corresponding to the first image) is displayed in white (corresponding to the second color) on the display unit 3 by the partial drive method. At this time, the entire surface of the display unit 3 is ideally white. However, it is known that an afterimage can be generated in the contour portion when the same area (corresponding to the first image) is reversed and displayed by the partial drive method. Therefore, the following first preliminary display process and second preliminary display process are executed.

  FIG. 15C shows the display image of the display unit 3 when the first preliminary display step (1) is executed, and the drive pixel 13 for that purpose. In the first preliminary display step (1), the pulse signal is driven so that the display unit 3 is black. However, if the entire surface is displayed completely in black, the image update process takes time, and the drive is stopped when a certain intermediate color (for example, light gray) is displayed as shown in FIG. At this time, the afterimage of the contour portion generated in the image erasing step (1) can be erased without taking time for the image updating process. In the present embodiment, the entire display unit is set to an intermediate color by the partial drive method.

  FIG. 15D shows the display image of the display unit 3 when the second preliminary display step (1) is executed, and the drive pixel 13 therefor. In the second preliminary display step (1), the pulse signal is driven so as to return the display unit 3 to white. At this time, the entire surface of the display unit 3 is white. In the present embodiment, the entire display unit is made white by the partial drive method.

  FIG. 15E shows the display image of the display unit 3 when the image display step (2) is executed again after the second preliminary display step (1), and the drive pixels 13 therefor. In the image display step (2), the time display 10:06 (corresponding to the first image) is displayed in black (corresponding to the first color) on the display unit 3 by the partial drive method.

  In the following, FIGS. 15F to 15H correspond to the case where the first image is time display 10:06 in FIGS. 15B to 15D, respectively, and the description thereof will be omitted. . In the examples of FIGS. 15A to 15H, display of a desired image and reverse display are not performed continuously. That is, the screen does not flicker.

  Here, the driving pixels 13 in the image display step (1) and the image erasing step (1) change the same object (first image) to black and white, respectively, and are in DC balance (see FIG. 15 (A) to f1 and g1) in FIG. 15 (B). In addition, the drive pixels 13 in the first preliminary display step (1) and the second preliminary display step (1) are changed to black and white, respectively, and are in DC balance (FIG. 15C). ~ J1 and k1 in FIG. 15 (D). Note that DC balance is similarly obtained for f2 and g2 in FIGS. 15E to 15F and j2 and k2 in FIGS. 15G to 15H. That is, in the driving method of the electrophoretic display device of this embodiment, DC balance is taken.

  Here, the reduction of the local contrast ratio by the partial drive method is examined. In the driving method of the electrophoretic display device of this embodiment, after the image display process and the image erasing process are performed, the entire surface including the background portion of the first image is driven by the first preliminary display process and the second preliminary display process. The Therefore, it is possible to avoid a large difference in the number of times of driving between the first image (corresponding to the specific area) and the background of the first image. As a result, a local reduction in contrast ratio is unlikely to occur.

  Therefore, the driving method of the electrophoretic display device according to the present embodiment does not cause local contrast ratio reduction or flickering while maintaining DC balance. Therefore, long-term reliability can be ensured and display quality can be improved.

4.3. Flowchart The control process performed by the control unit of the electrophoretic display device of this embodiment is as shown in the flowchart of FIG. As shown in FIG. 16, an image display step (S12) for displaying a first image (for example, time display) in a first color (for example, black) is executed. Then, an image erasing step (S14) is performed to erase the first image by displaying the first image in the second color (for example, white). Subsequently, a first preliminary display step (S22) for displaying the entire display unit in an intermediate color (for example, light gray) is performed. Then, a second preliminary display step (S24) for returning the entire display unit to the second color (for example, white) is performed. Then, after the second preliminary display step (S24), the process returns to the image display step (S12). In the present embodiment, the first preliminary display step and the second preliminary display step perform single color display by a partial drive method.

4.4. Waveform Diagram FIG. 17 is a waveform diagram of this embodiment. The same elements as those in FIGS. 4A to 4B and FIGS. 6A to 6B are denoted by the same reference numerals, and the description thereof is omitted. Further, the corresponding steps are the same as those shown in FIGS.

  In the present embodiment, the first preliminary display process and the second preliminary display process are executed. However, the purpose of these steps is to erase afterimages generated in the contour portion of the first image. Therefore, in the first preliminary display step, the entire display unit may be displayed in an intermediate color (for example, light gray), for example, by a partial drive method, and it is not necessary to display in black.

  Therefore, as shown in the waveform diagram of FIG. 17, the execution time of the first preliminary display step (1) and the second preliminary display step (1) may be shorter than that of the image display step (1). Therefore, even if the first preliminary display step and the second preliminary display step, which are partial driving methods, are executed, there is no problem that it takes time to update the display image. Further, in this embodiment, since the entire surface driving method is not used, the problem of afterimages that can be caused by shortening the driving time of the pulse signal does not occur.

5. Fifth Embodiment A fifth embodiment and a modification of the present invention will be described with reference to FIGS. In addition, the same code | symbol is attached | subjected about the same element as FIGS. 1-17, and description is abbreviate | omitted.

5.1. Display Example of this Embodiment FIGS. 18A to 18F show display examples of this embodiment. The process names in FIGS. 18A to 18F correspond to the process names in the flowchart described later. Also, the same elements as those in FIGS. 15A to 15H are denoted by the same reference numerals, and description thereof is omitted. Specifically, the processes in FIGS. 18A to 18D are the same as those in FIGS. 15A to 15D because the display image of the display unit 3 and the drive pixels 13 are the same. Omitted.

  In this embodiment, in addition to the steps of the fourth embodiment, all the pixels of the display unit 3 are black (corresponding to the first color) and white (first) as shown in FIGS. 18 (E) and 18 (F). Including a third preliminary display step and a fourth preliminary display step for display in two colors).

  As described above, the afterimage of the contour portion is not visually recognized by the first preliminary display step and the second preliminary display step, but there is a possibility that an afterimage that is not visually recognized by the user may be accumulated. Therefore, as time passes, color disturbance such as “haze” may occur in a part of the area including the first image (time display in this example) on the display unit of the electrophoretic display device. In the driving method of the electrophoretic display device of this embodiment, the entire display unit is displayed in the first color and the second color in the third preliminary display step and the fourth preliminary display step, respectively, and the entire display unit is refreshed. Such color disturbance can be prevented.

  Here, in the third preliminary display step and the fourth preliminary display step, since the entire display portion is displayed in black and white, respectively, DC balance is obtained (m1 in FIG. 18E and FIG. 18F). N1).

5.2. Flowchart The control process performed by the control unit of the electrophoretic display device of this embodiment is as shown in the flowchart of FIG. The same steps as those in FIG. 16 are denoted by the same reference numerals, and detailed description thereof is omitted.

  In this embodiment, following the image display step (S12), the image erasing step (S14), the first preliminary display step (S22), and the second preliminary display step (S24), the entire display unit is set to the first color (for example, black). The third preliminary display step (S26) displayed in () is executed. Thereafter, a fourth preliminary display step (S28) for displaying the entire display unit in the second color (for example, white) is performed. Then, after the fourth preliminary display step (S28), the process returns to the image display step (S12). In the present embodiment, the first preliminary display step, the second preliminary display step, the third preliminary display step, and the fourth preliminary display step perform single color display by a partial drive method.

5.3. Flowchart of Modified Example However, if the third preliminary display step (S26) and the fourth preliminary display step (S28) are always executed, there may be a problem that it takes time to update the display image. Therefore, the third preliminary display step (S26) and the fourth preliminary display step (S28) are performed on condition that the image display step (S12) is executed more than a predetermined number N ₀ (for example, N ₀ = 10). It may be broken.

  FIG. 20 is a flowchart of this modification. In addition, the same code | symbol is attached | subjected to the same step as FIG. 16, FIG. 19, and description is abbreviate | omitted.

First, the number N of times that the image display step (S12) has been executed is initialized to 0 (S11). When the image display process (S12) is executed, N is incremented (S13). After that, when it is executed more than a predetermined number N ₀ (for example, N ₀ = 10) (S25Y), the third preliminary display step (S26) and the fourth preliminary display step (S28) are executed, and the process proceeds to step S11. Return. If the number of image display step (S12) is performed N is equal to or less than a predetermined number _{N 0,} return to the image display step (S12).

  At this time, it is possible to prevent color disturbance while avoiding the problem that it takes time to update the display image.

6). Application Examples Application examples of the present invention will be described with reference to FIGS. 21 to 22B. In addition, the same code | symbol is attached | subjected about the element similar to FIGS. 1-20, and description is abbreviate | omitted. The electrophoretic display devices of the first to fifth embodiments and the modification examples can be applied to an electronic device such as an electronic timepiece that displays time.

6.1. FIG. 21 is a block diagram of an electronic device 1 according to an application example. The electronic device 1 includes a CPU 2, an input unit 4, a storage unit 5, and an electrophoretic display device 10. The electrophoretic display device 10 is the electrophoretic display device of the first embodiment, and includes a display unit 3 that displays various images.

  The CPU 2 controls other blocks and performs various calculations and processes. For example, the CPU 2 may read a program from the storage unit 5 and input a time signal or the like to the electrophoretic display device 10 according to the program.

  For example, the input unit 4 may receive an instruction from a user of the electronic device 1 and output a signal corresponding to the instruction to another block.

  The storage unit 5 may be, for example, a memory such as a DRAM or SRAM, or may include a ROM. The program used by the CPU 2 may be written in a ROM included in the storage unit 5, for example.

  The display unit 3 is a part of the electrophoretic display device 10 and may display, for example, a time, a character, a photograph, or the like.

  By including the electrophoretic display device 10 of the first to fifth embodiments and the modified example, the electronic apparatus 1 can suppress a local contrast ratio decrease and occurrence of an afterimage while maintaining a DC balance of the display image. it can. Therefore, an electronic device having excellent long-term reliability and good display quality can be realized.

6.2. Specific Examples of Electronic Devices FIGS. 22A to 22B show specific examples of electronic devices. FIG. 22A is a front view of an electronic timepiece 1000 which is one of electronic devices. The electronic timepiece 1000 is a wristwatch, for example, and includes a timepiece case 1002 and a pair of bands 1003 connected to the timepiece case 1002. A display unit 1004 which is the display unit 3 (see FIG. 21) of the electrophoretic display device 10 is provided on the front surface of the watch case 1002, and a time display 1005 is performed. Two operation buttons 1011 and 1012 are provided on the side surface of the watch case and function as the input unit 4 (see FIG. 21).

  For example, FIG. 22B is a perspective view of an electronic paper 1100 that is one of the electronic devices. The electronic paper 1100 is flexible and includes a display region 1101 that is the display unit 3 (see FIG. 21) of the electrophoretic display device 10 and a main body 1102.

  The electrophoretic display devices of the first to fifth embodiments and modified examples can be applied to various electronic devices including these specific examples. And such an electronic device can ensure the long-term reliability of a display part by having DC balance, and can improve display quality by suppressing the fall of a local contrast ratio and generation | occurrence | production of an afterimage. .

7). Others In the second embodiment, the fourth embodiment, and the fifth embodiment, the partial drive method is used even when all the pixels of the display unit are displayed in a single color. However, a full drive method may be used. Specifically, in the second embodiment, in the first single color display step and the second single color display step, all the pixels of the display unit may be displayed in the first color and the second color, respectively, by the entire surface driving method. . At this time, the first single color display step and the second single color display step are executed subsequent to the first image erasing step and the second image erasing step for displaying the entire surface in black and white, respectively. For this reason, the problem of afterimages that can be caused by shortening the driving time of the pulse signal by the full-surface driving method does not occur.

  In the fourth embodiment, in the first to second preliminary display steps, a single color display may be performed by a full drive method. At this time, the first preliminary display step and the second preliminary display step are executed following the image erasing step for displaying the entire surface in white. For this reason, the problem of afterimages that can be caused by shortening the driving time of the pulse signal by the full-surface driving method does not occur. Also in the first to fourth preliminary display steps in the fifth embodiment, for the same reason, single color display may be performed by the entire surface driving method.

  In the above-described embodiment, the electrophoretic display device is not limited to one that performs black and white two-particle electrophoresis using black particles and white particles, and may perform one-particle electrophoresis such as blue and white, Any combination other than black and white is acceptable.

  The driving method described above may be applied not only to the electrophoretic display device but also to a memory-type display unit. For example, ECD (Electrochromic Display = electrochromic display), ferroelectric liquid crystal display, cholesteric liquid crystal display, and the like.

  Furthermore, the electronic timepiece of the application example is not limited to a wristwatch, and can be widely applied to devices having a clock function such as a table clock, a wall clock, and a pocket watch.

  The present invention is not limited to these exemplifications, and includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations that have the same functions, methods, and results, or configurations that have the same objects and effects). In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that exhibits the same operational effects as the configuration described in the embodiment or a configuration that can achieve the same object. Further, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

DESCRIPTION OF SYMBOLS 1 ... Electronic device, 2 ... CPU, 3 ... Display part, 4 ... Input part, 5 ... Memory | storage part, 10 ... Electrophoretic display device, 11 ... Pixel, 13 ... Drive pixel, 35, 35A, 35B ... Pixel electrode, 37 ... Common electrode, 40, 40A, 40B ... Pixel, 48 ... Driving TFT (Thin Film Transistor), 49 ... Low potential power line (Vss), 50 ... High potential power line (Vdd), 51 ... Region, 55 ... Common Electrode wiring (Vcom), 60 ... Display control circuit, 61 ... Scan line drive circuit, 62 ... Data line drive circuit, 63 ... Controller, 64 ... Common power supply modulation circuit, 66 ... Scan line, 68 ... Data line, 70 ... Latch Circuit: 80: Switch circuit, 91: First pulse signal line (S ₁ ), 92: Second pulse signal line (S ₂ ), 120: Microcapsule, 126: Black particles, 127: White particles, 130: Element substrate, 13 DESCRIPTION OF SYMBOLS ... Counter substrate, 132 ... Electrophoretic element, 160 ... Memory | storage part, 350 ... Drive electrode layer, 360 ... Electrophoresis display layer, 370 ... Common electrode layer, 1000 ... Wristwatch, 1002 ... Watch case, 1003 ... Band, 1004 ... Display Part, 1005 ... time display, 1011 ... operation button, 1012 ... operation button, 1100 ... electronic paper, 1101 ... display area, 1102 ... main body

Claims (7)

Including a display unit having an electrophoretic element including electrophoretic particles between a pair of substrates and having a pixel capable of displaying a first color, a second color, and an intermediate color between the first color and the second color; A pixel electrode corresponding to the pixel is formed between one of the substrates and the electrophoretic element, and a common electrode facing the plurality of pixel electrodes is formed between the other substrate and the electrophoretic element. A method for driving an electrophoretic display device comprising:
A voltage based on a driving pulse signal that repeats a first potential and a second potential is applied to the common electrode, and a voltage based on an inverted signal of the driving pulse signal or a normal signal is applied to each of the plurality of pixel electrodes. The first image is displayed on the display unit by a partial drive method in which an image displayed on the display unit is rewritten by applying and moving the electrophoretic particles by an electric field generated between the pixel electrode and the common electrode. An image display step for displaying the first color;
After the image display step, an image erasing step for displaying the first image in the second color on the display unit by the partial drive method;
A first preliminary display step of displaying all pixels of the display unit in the intermediate color after the image erasing step;
After the first preliminary display step, a second preliminary display step of displaying all the pixels of the display unit in the second color,
A method for driving an electrophoretic display device, wherein a next image display step is executed after the second preliminary display step. The method for driving an electrophoretic display device according to claim 1,
The first preliminary display step and the second preliminary display step are:
By the partial drive method, all the pixels of the display unit are displayed in the intermediate color or the second color,
The method for driving an electrophoretic display device, wherein the time for applying the voltage based on the drive pulse signal is shorter than the time for applying the voltage based on the drive pulse signal in the image display step. The method for driving an electrophoretic display device according to claim 1,
A third preliminary display step of displaying all the pixels of the display unit in the first color;
A fourth preliminary display step, which is performed subsequent to the third preliminary display step, and displays all the pixels of the display unit in the second color,
When a given condition is satisfied, the third preliminary display step and the fourth preliminary display step are performed after the second preliminary display step and before the next image display step is performed. Driving method of electrophoretic display device. The method for driving an electrophoretic display device according to claim 3,
The given condition is a method of driving an electrophoretic display device, wherein the image display step is executed a predetermined number of times.   An electrophoretic display device comprising a control unit that executes the method for driving an electrophoretic display device according to claim 1.   An electronic apparatus comprising the electrophoretic display device according to claim 5.   An electronic timepiece including the electrophoretic display device according to claim 5.