JP2012118349A - Driving method of electrophoretic display device, electrophoretic display device and electronic clock - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate afterimage of a contour portion with a good DC balance without significantly increasing the number of processing steps while displaying images without causing discomfort to a user.SOLUTION: A driving method of an electrophoretic display device, which holds electrophoretic elements between a pair of substrates and includes a display comprising pixels capable of displaying at least a first color and a second color, includes the following steps: a partial rewriting step S2 for rewriting a predetermined visual representation including at least a first visual representation and a second visual representation by applying voltage to the electrophoretic elements at the inside of a predetermined region of the display; and an asymmetry dissolving step S6 for dissolving asymmetry of the voltage applied to the electrophoretic elements in the partial rewriting step S2. The asymmetry dissolving step S6 is subsequently performed after rewriting of the first visual representation in the partial rewriting step S2, is followed by a first entire writing step for displaying the second visual representation by the second color and includes a reversely displayed portion eliminating step for displaying the pixels constituting a first fixed image by the first color so as to eliminate the second visual representation.

Description

  The present invention relates to a method for driving an electrophoretic display device, an electrophoretic display device, 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.

  In the electrophoretic display device, it is required to achieve DC balance, that is, to make the time average of the electric field applied between the electrodes substantially zero. Patent Document 1 points out the possibility that the operating life of the apparatus is shortened when the DC balance is lost. In other words, in order to ensure long-term reliability of the electrophoretic display device, it is necessary to perform drive control with a DC balance.

JP-T-2005-530201

  In the electrophoretic display device, in order to increase the response speed, not only full-surface driving for drawing the entire display unit but also partial driving for drawing only a part to be rewritten may be performed. For example, only the pixels constituting the displayed image are partially driven to erase the image. At this time, an electric field in an oblique direction is generated between a part of pixels to be rewritten and a background pixel, and an image with an expanded contour portion is displayed. May occur. In order to improve the appearance of the display image, it is preferable to include a step of erasing the afterimage in the drive control of the electrophoretic display device.

  At this time, it is necessary to balance the electric field applied in the process of erasing the afterimage. However, during the process of balancing the DC, since normal display is not performed, the user viewing the display unit feels uncomfortable. there is a possibility.

  The present invention has been made in view of such problems. According to some aspects of the present invention, an electrophoretic display device that performs afterimage erasure of a contoured portion with a DC balance without significantly increasing processing steps while performing display that does not give the user a sense of incongruity Driving method, electrophoretic display device, electronic timepiece, and the like can be provided.

(1) The present invention drives an electrophoretic display device that includes an electrophoretic element including electrophoretic particles between a pair of substrates and includes a display unit including pixels capable of displaying at least a first color and a second color. A method for rewriting a given visual expression including at least a first visual expression and a second visual expression by applying a voltage to the electrophoretic element within a given region of the display unit. Performing the partial rewriting step, and removing the asymmetry of the voltage applied in the partial rewriting step after the partial rewriting step is repeated a given number of times, the partial rewriting step Partially displaying a visual expression forming pixel that is a pixel forming the given visual expression in the first color, and partially erasing the display of the visual expression forming pixel in the second color. The given An afterimage erasing step for displaying pixels constituting a fixed image inside the area in the second color, and the afterimage erasing step is performed again when the given visual representation is the second visual representation. An afterimage erasing step, and if the given visual representation is the first visual representation, the first fixed image is used as the fixed image; otherwise, the fixed image The asymmetry elimination step is performed after the first visual representation is rewritten in the partial rewriting step, and the electrical display is performed in all areas of the display unit. After the first full-surface writing step and the first full-surface writing step, performing full-surface driving to apply a voltage to the electrophoretic element and displaying the visual expression forming pixels of the second visual expression in the second color, The pixels that make up the first fixed image Displayed in the first color, the inverted display part erasing step, and the number of times the pixels constituting the second fixed image are displayed in the second color in the partial rewriting step after the inverted display part erasing step, After the afterimage erasing symmetrizing step and the afterimage erasing symmetrizing step, the process of displaying the pixels constituting the second fixed image in the first color is repeated, and the second visual expression A second entire writing step for displaying the visual expression forming pixels of the first color, and the partial rewriting step is performed again after the second entire writing step.

  According to the present invention, the asymmetry of the applied electric field generated in the partial rewriting process can be eliminated by performing the asymmetry elimination process, and a DC balance can be achieved. By taking DC balance, an electrophoretic display device with high long-term reliability can be provided. The partial rewriting process includes an afterimage erasing process for erasing an afterimage along the contour of a given visual expression. Since the afterimage can be erased, an electrophoretic display device with high visibility can be provided.

  Here, the process of eliminating the asymmetry is performed by displaying an area where partial driving can be performed, for example, in black, and then displaying pixels in which the applied electric field is biased in black. Therefore, the user does not visually recognize an unnecessary display during processing. However, at least a part of the normal display continues to be displayed in black during the process. Therefore, the user may feel uncomfortable with the display. In the present invention, the asymmetry elimination step is performed after the first visual representation is rewritten. In the asymmetry elimination process of the present invention, first, the second visual expression is displayed, and then the processing for eliminating asymmetry is performed. Since the user can first recognize that the display has changed from the first visual expression to the second visual expression, even if a time during which normal display is not performed thereafter occurs, the display does not feel uncomfortable.

  In the afterimage erasing step, the reverse display partial erasing step, and the afterimage erasing symmetrization step of the present invention, the afterimage is erased using a fixed image. In the present invention, the first and second fixed images are used. For example, in the reverse display partial erasing step, the first fixed image generated based on the visual expression itself to be processed is used. Also, for example, in the afterimage erasing symmetrization step, a second fixed image including a contour portion of a visual expression to be processed (a portion including the contour of the visual representation and remaining as an afterimage) is used. In the present invention, an increase in processing steps can be suppressed by properly using the first fixed image and the second fixed image.

  Here, the first color and the second color are two colors that are basic colors that can be displayed at least by the electrophoretic display device. For example, in a two-particle microcapsule type electrophoresis system, the dispersion liquid is colorless and transparent, and the electrophoretic particles are white or black. This type of electrophoretic display unit is capable of displaying at least two colors, with white or black as the basic colors. At this time, black, which is one color of the electrophoretic particles, may be assigned as the first color, and white may be assigned as the second color. Conversely, white may be assigned as the first color and black may be assigned as the second color. The given area in the display unit refers to an area where a given visual expression can be rewritten by partial driving. The given visual expression may be any one of letters, numbers, messages, images, figures, patterns, symbols, etc., or a combination or part thereof.

  The display of the visual expression forming pixels in the second color by the entire surface driving includes an operation of setting the background of the visual expression to the first color in an area where the partial driving can be performed (given area). Further, the fixed image means a fixed pattern image and indicates a pixel to be partially driven.

(2) In this method for driving an electrophoretic display device, an image obtained by combining the first visual expression and the second visual expression may be used as the first fixed image.

  According to the present invention, the first fixed image is represented by an image obtained by combining the first visual expression and the second visual expression, that is, a set of pixels constituting these visual expressions. It may be an image. By using such a first fixed image in the inverted display partial erasing step or the like, it is possible to perform partial erasure of the inverted display while suppressing an increase in the number of processing steps, thereby obtaining DC balance.

  The second fixed image may be, for example, an image obtained by synthesizing the contour forming pixels and the background boundary pixels for all visual representations other than the first visual representation, that is, an image represented by a set of these pixels. Good. A contour forming pixel is a pixel that forms a contour of visual expression, and a background boundary pixel is a background pixel (a pixel that does not form a visual expression) adjacent to the contour forming pixel. The contour forming pixel and the background boundary pixel can become an afterimage due to an oblique electric field generated during partial driving. Further, the second fixed image may be a closed graphic including all contour forming pixels and background boundary pixels of a visual expression other than the first visual expression, for example. The closed figure here means a figure closed on the outer periphery.

(3) In the driving method of the electrophoretic display device, the given number of times may be a plurality of times.

  According to the present invention, after the partial rewriting process is repeated a plurality of times, the process proceeds to the asymmetry elimination process. In the asymmetry elimination process, DC asymmetry is taken together for the asymmetry of the applied voltage generated in the partial rewriting process. For this reason, the efficiency of the entire process is increased.

  At this time, there are only two types of fixed images used in the afterimage elimination symmetrization process. Therefore, it is only necessary to read the information of the fixed image twice from the storage unit. For this reason, it is possible to avoid a delay in processing time and an increase in power consumption due to access to the storage unit. In particular, when the number of partial rewrite steps is repeated, the effect of reducing the processing time and power consumption is great.

(4) The present invention is an electrophoretic display device, in which an electrophoretic element including electrophoretic particles is sandwiched between a pair of substrates, and a display unit including pixels capable of displaying at least a first color and a second color And a control unit that controls the display unit, wherein the control unit applies at least a first visual expression by applying a voltage to the electrophoretic element within a given region of the display unit. Partial rewriting control for rewriting a given visual expression including the second visual expression, and eliminating the asymmetry of the voltage applied in the partial rewriting control after the partial rewriting control is repeated a given number of times The partial rewrite control, and in the partial rewrite control, the visual representation forming pixels that are pixels forming the given visual representation are displayed in the first color, and the visual representation Before forming pixel The partial erasure control for displaying in the second color, the afterimage erasure control for displaying the pixels constituting the fixed image in the given area in the second color, and the given visual expression are the second If the visual representation is the first visual representation, the afterimage erasing control is performed again. When the given visual representation is the first visual representation, the first image is used as the fixed image. The fixed image is used, otherwise the second fixed image is used as the fixed image, and the asymmetry is performed after the first visual expression is rewritten by the partial rewrite control. In the resolution elimination control, the entire surface drive for applying a voltage to the electrophoretic element is performed in all areas of the display unit, and the visual expression forming pixels of the second visual expression are displayed in the second color. Full writing control and the first full writing After the image control, the pixels constituting the first fixed image are displayed in the first color, and the second fixed by the partial rewrite control after the reverse display partial erase control and the reverse display partial erase control. The afterimage erasing symmetrization control and the afterimage erasing symmetrization which repeat the process of displaying the pixels constituting the second fixed image in the first color as many times as the pixels constituting the image are displayed in the second color. After the control, the whole surface drive is performed, and the second visual writing forming display of the visual expression forming pixels of the second visual expression is displayed in the first color, and after the second full surface writing control, The partial rewrite control is performed again.

  According to the present invention, the asymmetry of the applied electric field caused by the partial rewrite control can be eliminated by performing the asymmetry elimination control, and a DC balance can be achieved. By taking DC balance, an electrophoretic display device with high long-term reliability can be provided. Here, the partial rewriting control includes afterimage erasing control for erasing the afterimage along the contour of a given visual expression. Since the afterimage can be erased, an electrophoretic display device with high visibility can be provided.

  In the present invention, the asymmetry elimination control is performed after the first visual expression is rewritten. And the asymmetry elimination control of this invention implements the process which eliminates asymmetry after displaying a 2nd visual expression first. Since the user can first recognize that the display has changed from the first visual representation to the second visual representation, even if there is a time during which normal display is not performed due to the process of eliminating asymmetry after that, You don't feel uncomfortable.

  In the afterimage erasure control, the reverse display partial erasure control, and the afterimage erasure symmetrization control according to the present invention, the first and second fixed images are used. In the present invention, an increase in processing steps can be suppressed by properly using the first fixed image and the second fixed image.

(5) In this electrophoretic display device, the control unit may use an image obtained by synthesizing the first visual expression and the second visual expression as the first fixed image.

  According to the present invention, the first fixed image is represented by an image obtained by combining the first visual expression and the second visual expression, that is, a set of pixels constituting these visual expressions. It may be an image. By using such a first fixed image in the reverse display partial erase control or the like, it is possible to perform the partial display of the reverse display while suppressing the increase in the number of processing steps, and to obtain DC balance.

(6) The present invention is an electronic timepiece including the electrophoretic display device, wherein the display unit performs time display including at least an hour digit and a minute digit, and the control unit performs the partial rewriting control, Let the minute digits of the time display be the given visual representation.

(7) In this electronic timepiece, the control unit may perform the afterimage erasing symmetrization control once every 10 minutes, and the control unit may set the first visual expression to 9 and the second visual expression to 0. .

  According to these inventions, the control unit performs partial rewrite control for the minute digit display of the electronic timepiece whose display changes every minute. At this time, afterimage elimination symmetrization control may be performed when the first digit of the minute digit changes from 9 to 0. Even when the afterimage erasing symmetrization control is executed, since the time display is first performed and the state shifts to a state in which a part of the time display is not displayed, the user does not feel discomfort.

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. FIGS. 4A to 4C are views showing a display example of partial driving and afterimage erasing in the first embodiment, and a cross-sectional view cut along a YY line. FIG. 5A to FIG. 5B are diagrams for explaining a contour forming pixel and a background boundary pixel. FIG. 6A to FIG. 6F are diagrams for explaining a fixed image. 5 is a flowchart of a method for driving the electrophoretic display device according to the first embodiment. 8A and 8B are flowcharts of the subroutine of FIG. FIG. 9 is a diagram of a wrist watch which is an example of an electronic timepiece. 10A to 10J are diagrams showing display examples of an electronic timepiece in a comparative example. 11A to 11N are diagrams illustrating display examples of an electronic timepiece in an application example.

  Embodiments of the present invention will be described below with reference to the drawings. In the description of the application example, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

1. First Embodiment A first embodiment of the present invention will be described with reference to FIGS.

1.1. Electrophoretic display device 1.1.1. Configuration of Electrophoretic Display Device FIG. 1 is a block diagram of an active matrix driving type electrophoretic display device 100 according to the present embodiment.

  The electrophoretic display device 100 includes a control unit 6, a storage unit 160, and a display unit 5. The control unit 6 controls the display unit 5 and includes a scanning line driving circuit 61, a data line driving circuit 62, a controller 63, and a common power supply modulation circuit 64. The scanning line driving circuit 61, the data line driving circuit 62, and the common power supply modulation circuit 64 are each connected to the controller 63. The controller 63 comprehensively controls these based on an image signal read from the storage unit 160 and a synchronization signal supplied from outside the figure. The control unit 6 may include a storage unit 160. For example, the storage unit 160 may be a memory built in the controller 63.

  Here, the storage unit 160 may be an SRAM, DRAM, or other memory, and stores at least image data (image signal) to be displayed on the display unit 5. In addition, information necessary for control by the controller 63 is stored in the storage unit 160. The information necessary for the control is, for example, the number of times the afterimage erasing step S24 (see FIG. 8A) has been executed. At this time, the controller 63 can determine the number of times to repeat the symmetrization process in the afterimage erasing symmetrization step S62 (see FIG. 8B) based on the information.

  The display unit 5 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 (Y ₁ , Y ₂ ,..., Y _m ). The scanning line driving circuit 61 specifies the on-timing of the driving TFT 41 (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 (X ₁ , X ₂ ,..., X _n ). 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 the present embodiment, when defining pixel data “0”, a low-level image signal is supplied to the pixel 40, and when defining image data “1”, a high-level image signal is applied to the pixel 40. 40.

The display unit 5 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 (S) extending from the common power modulation circuit 64. ₁ ), 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.

1.1.2. 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) 41, 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 41 is a pixel switching element made of an N-MOS transistor. The gate terminal of the driving TFT 41 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. A power supply voltage is supplied to the inverters 70t and 70f 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.

Image data "1" in the latch circuit 70 (the image signal of high level) is stored, the transmission gate TG1 is turned on, the switch circuit 80 supplies the signals S ₁ as Va. On the other hand, the image data "0" in the latch circuit 70 (the image signal of a low level) is stored, when the transmission gate TG2 is turned on, the switch circuit 80 supplies the signal S ₂ as Va. With such a circuit configuration, the control unit 6 can control the potential (signal) supplied to the pixel electrode of each pixel 40. The circuit configuration of the pixel 40 is an example, and is not limited to that shown in FIG.

1.1.3. Display Method The electrophoretic display device 100 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, the electrophoretic display device 100 will be described as displaying black as the first color and white as the second color. Displaying pixels displaying black (first color) in white (second color) or displaying pixels displaying white in black is expressed as inversion.

  FIG. 3A is a diagram showing a configuration of the electrophoretic element 32 of the present embodiment. The electrophoretic element 32 is sandwiched between an element substrate 30 and a counter substrate 31 (see FIGS. 3B and 3C). The electrophoretic element 32 is configured by arranging a plurality of microcapsules 20. The microcapsule 20 encloses, for example, a colorless and transparent dispersion, a plurality of white particles (electrophoretic particles) 27, and a plurality of black particles (electrophoretic particles) 26. In the present embodiment, for example, it is assumed that the white particles 27 are negatively charged and the black particles 26 are positively charged.

  FIG. 3B is a partial cross-sectional view of the display unit 5 of the electrophoretic display device 100. The element substrate 30 and the counter substrate 31 sandwich an electrophoretic element 32 in which the microcapsules 20 are arranged. The display unit 5 includes a drive electrode layer 350 in which a plurality of pixel electrodes 35 are formed on the electrophoretic element 32 side of the element substrate 30. 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 31 is a transparent substrate, and an image is displayed on the counter substrate 31 side in the display unit 5. The display unit 5 includes a common electrode layer 370 in which a common electrode 37 having a planar shape is formed on the electrophoretic element 32 side of the counter substrate 31. 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 32 is disposed in 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 area. 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 common electrode side potential Vcom is higher than the potential Va of the pixel electrode of the pixel 40A. At this time, since the negatively charged white particles 27 are attracted toward the common electrode 37 and the positively charged black particles 26 are attracted toward the pixel electrode 35A, the pixel 40A is visually recognized as displaying white.

  In FIG. 3C, the common electrode side potential Vcom 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 26 are attracted to the common electrode 37 side, and the negatively charged white particles 27 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. 3B and 3C, Va, Vb, and Vcom are described as fixed potentials. Actually, Va, Vb, and Vcom are pulse signals whose potentials change with time.

1.2. Driving method of electrophoretic display device 1.2.1. Afterimage of Contour Part As a driving method of the electrophoretic display device, not only full-surface driving for drawing the entire display unit but also partial driving for drawing only a part of the display unit to be rewritten may be used. By reducing the number of pixels to which the voltage is applied, the response at the time of rewriting can be accelerated.

  However, when partial driving is performed, an electric field is generated in an oblique direction at a boundary portion with a pixel (background) that is not driven. When characters, numbers, figures, etc. displayed by partial driving are erased, the outlines of the characters, numbers, figures, etc. may be visually recognized as an afterimage due to the influence of an electric field generated in an oblique direction. Therefore, when partial rewriting is performed by partial driving (partial rewriting), an operation (afterimage erasing) for erasing the afterimage of the contour portion is necessary.

  4A to 4C show a display example (left diagram) and a cross-sectional view (right diagram) of the display unit 5 when partial writing, partial erasing, and afterimage erasing are performed, respectively. In FIGS. 4A to 4C, 6 pixels × 6 pixels are extracted from a given area where partial driving can be performed in the display unit 5 and displayed. 4A to 4C are cross-sectional views taken along line YY in the left diagram, and include pixels 40A and 40B. 4 (A) to 4 (C) and FIGS. 5 (A) to 5 (B), the pixels indicated by diagonal lines in the display portion 5 indicate that the pixels are displayed in black. Show. In a given area in the display unit, a given visual expression is rewritten by partial driving. The given visual expression is any one of letters, numbers, messages, images, figures, patterns, symbols, etc., or a combination or part thereof.

In FIGS. 4A to 4C, Va and Vb are signals supplied to the pixel electrode 35A of the pixel 40A and the pixel electrode 35B of the pixel 40B, respectively. Note that the pixel 40A and the pixel 40B are adjacent to each other (see FIGS. 3B and 3C). Also the circuit configuration of the pixel 40A and the pixel 40B are the same as FIG. 2, in accordance with the image data stored in the respective latch circuits, Va, and outputs the S ₁ or S ₂ as Vb. Vcom is a signal supplied from the common power supply modulation circuit 64 to the common electrode 37. Each of the signals Va, Vb, and Vcom can assume a high level (VH), a low level (VL), or a high impedance state (Hi-Z). In this example, when the signal supplied to the pixel electrode 35B is Hi-Z, no consideration is given to an electric field generated in an oblique direction.

  FIG. 4A shows a case where partial writing is performed. An image P1 is written as a visual expression on the display unit 5, and the pixel 40A is one of the pixels (contour forming pixels) forming the contour. The black 16 pixels (4 pixels × 4 pixels) forming the image P1 are visual expression forming pixels. The contour forming pixel is a pixel that is a part of the visual expression forming pixel and is at the boundary with the background. The pixel 40B is one pixel included in the background, and is one of the pixels (background boundary pixel) adjacent to the contour forming pixel. Looking at the right figure, the potential of the pixel electrode 35A (Va) is VH, and the pixel 40A is displayed in black. On the other hand, the pixel electrode 35B (Vb) is in a high impedance state, for example, and the pixel 40B maintains a white display as a background color.

  Here, the contour forming pixel R3 and the background boundary pixel R4 in the image P1 will be described with reference to FIGS. 5 (A) to 5 (B). As shown in FIG. 5A, the contour forming pixel R3 is twelve black pixels that form the contour of the image P1. One of them is the pixel 40A. As shown in FIG. 5B, the background boundary pixel R4 is 16 pixels of the background (white) adjacent to the contour forming pixel R3, and one of them is the pixel 40B. In the present embodiment, the term “adjacent” refers only to the horizontal and vertical directions, but may include an oblique direction. For example, in FIG. 5B, the pixel 40V, the pixel 40W, the pixel 40X, and the pixel 40Y may be included in the background boundary pixels.

  FIG. 4B shows a case where partial erasure is performed. Partial erasure is performed by displaying the pixels (visual expression forming pixels) forming the image P1 written by the partial writing in white. The potential of the pixel electrode 35A (Va) is VL, and the pixel 40A is white. At this time, since an electric field in an oblique direction is generated between the contour forming pixel and the background boundary pixel in the high impedance state (Hi-Z) adjacent thereto, the image P1 is an image in which the contour portion is swollen. An afterimage P2 along the contour is generated. In this example, with a white background, a thin black afterimage P2 is visually recognized along the contour. Therefore, it is necessary to delete the next afterimage.

  FIG. 4C shows a case where afterimage erasure is performed. In order to erase the afterimage P2 of the outline, it is necessary to display an image including at least the outline forming pixel R3 and the background boundary pixel R4 of the image P1 in the same white color as the background color. At this time, the pixel 40A included in the contour forming pixel R3 and the pixel 40B included in the background boundary pixel R4 are also displayed in white. In the right figure, the potentials of the pixel electrodes 35A (Va) and 35B (Vb) of the pixels 40A and 40B are VL, and an electric field in a direction in which the negatively charged white particles 27 are attracted to the common electrode 37 side is applied. Yes. Then, the afterimage P2 of the outline is deleted.

  Note that afterimage erasing is required only when partial driving is performed. When full-surface driving is performed, all pixels are to be driven, and an electric field is not easily generated in an oblique direction. Therefore, afterimage erasing is not necessary in the case of full-surface driving.

1.2.2. The DC balance afterimage erasure is an additional process different from the display and erasure of characters, numbers, figures, etc. themselves. In addition, the time during which the electric field is applied in the afterimage erasing step is shorter than that for displaying and erasing characters, numbers, figures, etc. themselves. Therefore, conventionally, DC balance has not been considered for afterimage removal.

  However, an electric field is applied in a certain direction between the electrodes of the pixel that is the target of the afterimage erasure by the afterimage erasure. Since afterimage erasure is repeated with the display of characters, numbers, graphics, etc. itself, the asymmetry of the applied electric field increases as it continues to be used. Therefore, in order to ensure long-term reliability of the electrophoretic display device, it is necessary to balance DC including afterimage erasure. Therefore, in order to eliminate the asymmetry of the applied electric field caused by the afterimage erasure, the following afterimage erasure symmetry is performed.

  Note that the pixels on which partial writing has been performed in FIG. 4A are DC balanced by partial erasing in FIG. 4B. The visual expression forming pixels displayed in black including the pixel 40A are displayed in white by partial erasure. At this time, the time average of the electric field applied between the electrodes for the visual expression forming pixel is zero and DC balance is achieved. Therefore, it is necessary to eliminate asymmetry for pixels to which an electric field is applied in the afterimage erasing step.

1.2.3. Problems in Performance in Afterimage Elimination Symmetry Here, in the afterimage elimination symmetrization, pixel information that needs to be DC balanced needs to be read out from the storage unit 160 (see FIG. 1) as an image signal. In the afterimage elimination symmetrization step, afterimage elimination performed for a plurality of visual expressions is preferably symmetrized collectively (DC balance) from the viewpoint of processing efficiency. However, when the pixels that need to be DC-balanced differ for each visual expression, for example, it is necessary to access the storage unit 160 a plurality of times to acquire an image signal. This may reduce the response speed of the electrophoretic display device and increase power consumption. In addition, since it is necessary to save all data representing pixels that need to be DC balanced for each visual expression in the storage unit 160, there may be a cost problem that a large storage capacity is required.

  Therefore, these problems are solved by fixing the pixels to be partially driven in the afterimage erasing and afterimage erasing symmetrization process as much as possible, that is, by driving the pixels constituting one or two fixed images. can do. Note that the display color is reversed between the fixed image in the afterimage erasure and the fixed image in the afterimage symmetrization. However, in both cases, the pixels to be driven are the same, and they are called fixed images without any particular distinction.

1.2.4. Display Problems in Afterimage Elimination Symmetry For the afterimage elimination symmetrization, it is preferable that the display in the process is not visually recognized by the user. For example, if the pixel that constitutes the fixed image is displayed in black after the area to be partially written is displayed in black, for example, the fixed image and the surrounding area are the same black, and thus are not visible to the user. However, at least a part of the normal display continues to be displayed in black during the afterimage erasing symmetry.

  In particular, when a display change is expected at a predetermined timing such as time display, if such a black display occurs when the display should change, the user may not be able to recognize the expected change and feel uncomfortable There is sex.

  Therefore, in the first process of the afterimage elimination symmetrization, this problem is solved by inverting the visual expression to be displayed, for example, in white. Since the user can recognize the visual expression to be displayed before viewing the black display, the user does not feel uncomfortable with the display. Note that the visual expression to be displayed indicates the second visual expression when the first visual expression changes to the second visual expression. Below, it demonstrates using this 1st and 2nd visual expression.

  Here, in order to realize reverse display by partial driving, it is necessary to add four processing steps of partial writing, partial erasing, afterimage erasing, and afterimage erasing symmetrization. However, from the viewpoint of processing speed, it is preferable that the number of additional processing steps is small. Therefore, it is considered to perform the reverse display by using full-surface writing (first full-surface writing) performed after the afterimage deletion of the first visual expression and before the afterimage symmetrization process.

  Since the first full write is performed by full drive, it is not necessary to achieve DC balance. For this reason, it is only necessary to add a step of partial erasure (partial erasure of reverse display) so that afterimage display is reversed by full-surface writing so that afterimage erasure symmetry can be performed. Due to the partial erasure of the reverse display, the entire area to be partially written is displayed in black.

  However, the second full-surface write for achieving DC balance is performed with respect to the first full-surface write (reversed display). At this time, in the second full-surface writing, the second visual expression is displayed in black. Therefore, since there is a possibility that an afterimage may remain strongly in the contour portion of the second visual expression, it is preferable to further add two steps of afterimage elimination and afterimage elimination symmetry. However, in total, only three steps are added, and the number of steps can be reduced as compared with the case where reverse display is realized by partial driving.

  In the added partial erase (reverse display partial erase) step, specifically, a fixed image is displayed in black. On the other hand, in the first visual representation afterimage erasing step performed immediately before the first full-surface writing, specifically, a fixed image is displayed in white. Here, in the first visual representation afterimage erasing step, the entire image is written immediately thereafter, so that there is little need to perform afterimage erasure. Accordingly, it is efficient to achieve DC balance between the added partial erasure (reverse display partial erasure) step and the first visual representation afterimage erasure step. Therefore, a first fixed image used in common between these steps is prepared. By this method, it is possible to perform display so as not to give the user a sense of incongruity without greatly increasing the number of processing steps, and to achieve DC balance. Note that the fixed image used in the afterimage elimination and afterimage elimination symmetrization process other than the first visual expression is referred to as a second fixed image in distinction from this.

1.2.5. Fixed Image First, the second fixed image used in the afterimage elimination and afterimage elimination symmetries other than the first visual representation needs to include contour forming pixels and background boundary pixels of the visual representation other than the first visual representation. There is. This is because the contour forming pixel and the background boundary pixel can be visually recognized as an afterimage. The second fixed image may be an image formed by synthesizing the contour forming pixels and background boundary pixels of all displayed visual expressions. Combining means, for example, a process in which 1 is assigned to the contour forming pixels and background boundary pixels of each visual expression, 0 is assigned to the other pixels, and a logical sum is obtained for each target visual expression. To do. That is, the second fixed image is an image represented by a set of all the contour forming pixels and the background boundary pixels of the visual expression other than the first visual expression.

  Further, the second fixed image may be a closed graphic including contour forming pixels and background boundary pixels of visual expressions other than the first visual expression. The closed figure means a figure closed at the outer periphery, and includes a figure having a shape such as a polygon (for example, a rectangle), a circle, or an ellipse.

  On the other hand, the first fixed image is used for erasing the second visual expression displayed in reverse and displaying the area in which partial driving is performed in black. In the first visual representation afterimage erasing step, the afterimage is used to make the afterimage as inconspicuous as possible. Then, the first fixed image is preferably an image obtained by combining the first visual expression and the second visual expression. By using such a first fixed image, unnecessary pixels need not be driven.

  A specific example of a fixed image will be described with reference to FIGS. In this example, it is assumed that all displayed visual expressions are the numbers (0 to 9) shown in FIG. At this time, the images represented in black in FIGS. 6D and 6E show examples of the second fixed image. FIG. 6F shows an example of a first fixed image. In this example, the given area where the visual expression is displayed is an area of 12 pixels × 12 pixels, where the first visual expression is 9 and the second visual expression is 0. That is, when changing from 9 to 0, the first full-surface driving is performed to perform reverse display, and then afterimage erasing symmetry is performed.

  First, the second fixed image is used when the numbers 0 to 8 are represented as visual expressions. FIG. 6B is an image (black portion) obtained by synthesizing the contour forming pixels of the numbers 0 to 8. FIG. 6C shows an image (shaded portion) in which background boundary pixels of all visual expressions are synthesized. Note that the black portion is the same as in FIG. Since the second fixed image needs to include contour forming pixels and background boundary pixels for all visual representations, the black portion in FIG. 6B and the shaded portion in FIG. 6C are combined. 6 (D) image (black portion). The image in FIG. 6D is the smallest second fixed image in this example.

  Further, the second fixed image may be a closed figure such as a quadrangle in which the outer periphery and the area closed on the outer periphery are represented by a single color. Therefore, the second fixed image may be an image represented by a black rectangle in FIG.

  In the case of FIG. 6D, the second fixed image with the fewest number of pixels to be driven is obtained. In the case of FIG. 6 (E), it is only necessary to store the information on the outer peripheral pixels or the information on the vertices. Therefore, the amount of data for storing the second fixed image is smaller than in FIG. 6 (D). It is possible to reduce.

  FIG. 6F is an image obtained by synthesizing the first visual expression (number 9) and the second visual expression (number 0), and represents the first fixed image in this example.

1.2.6. Flowchart of Main Routine FIG. 7 is a flowchart of the driving method of the electrophoretic display device in the first embodiment. In the driving method of the electrophoretic display device according to the present embodiment, the partial rewriting step S2 is first performed. In the partial rewriting step S2, a given visual expression is rewritten by partial driving in a given area in the display unit of the electrophoretic display device. For example, it is assumed that the numbers 0 to 9 are rewritten to a region of 12 pixels × 12 pixels by partial driving, and the other regions of the display unit are rewritten only by full-surface driving. At this time, the given area is an area of 12 pixels × 12 pixels, and the given visual expression is a number from 0 to 9.

  The partial rewriting step S2 may be repeated a given number of times (S4). In the previous example, assuming that 0 to 9 are displayed once in order, the partial rewriting step S2 is repeated 10 times.

  Thereafter, in order to eliminate the imbalance of DC balance (asymmetry of the applied electric field) caused by the afterimage erasing process included in the partial rewriting process S2, the asymmetry eliminating process S6 is performed. After the asymmetry elimination step S6, it may be determined whether or not there is an end command for display on the electrophoretic display device (S8). When the display is continued, the process returns to S2 again (S8N), and when the display is ended, the control of the flowchart is also ended (S8Y). For example, in an electrophoretic display device or the like used for an electronic timepiece, the display does not end and the steps S2 to S6 are repeated again.

1.2.7. Subroutine flowchart 1.2.7.1. Partial Rewriting Process FIG. 8A is a flowchart showing a subroutine of the partial rewriting process S2. In the present embodiment, the partial rewriting step S2 includes a partial writing step S20, a partial erasing step S22, an afterimage erasing step S24, and an additional afterimage erasing step S26.

  The partial writing step S20 displays a given visual expression in a given area of the display unit. Assume that a given visual representation includes at least a first visual representation and a second visual representation. Using the previous example again, in the partial writing step S20, when all of the area of 12 pixels × 12 pixels (given area) is white, the number of black (for example, given visual) is black by partial driving. Display). In this example, it is assumed that the first visual expression is 9 and the second visual expression is 0.

  The partial erasing step S22 erases the given visual expression written in the partial writing step S20. In the partial erasing step S22, for example, erasing is performed by displaying a white number 0 by partial driving. In the partial erasing step S22, DC is balanced with the partial writing step S20 by reversing colors and performing the same display. It is assumed that the direction of the applied electric field is the opposite between the case where white is displayed and the case where black is displayed, and the time during which the electric field is applied is the same.

  The afterimage erasing step S24 mainly erases the afterimage of the contour portion of a given visual expression. In the afterimage erasing step S24, for example, the afterimage of the 0-number outline portion is erased by displaying the fixed image in white by partial driving. However, since the DC balance is not achieved in the afterimage erasing step S24, the following asymmetry elimination step is necessary. Here, the first fixed image and the second fixed image are selectively used as the fixed image. If the given visual representation is the first visual representation, the first fixed image (see FIG. 6F) is used; otherwise, the second fixed image (FIG. 6D) ) Or FIG. 6 (E))).

  The additional afterimage erasing step S26 is performed only when the given visual expression is the second visual expression (S25Y), and is not performed otherwise (S25N). The additional afterimage erasing step S26 erases the afterimage of the contour portion of the second visual expression. This is because the second visual representation is written in the second full-surface writing step S64 (see FIG. 8B), so that an afterimage along the outline of the second visual representation remains strong, and the afterimage erasing step once again. This is because it is necessary to perform the above. Since DC balance is not taken in this step S26, the following asymmetry elimination step is required.

1.2.7.2. Asymmetry Resolving Step FIG. 8B is a flowchart showing a subroutine of the asymmetry resolving step S6. In the present embodiment, the asymmetry elimination step S6 includes a first full surface writing step S60, a reverse display partial erasing step S61, an afterimage erasing symmetrization step S62, and a second full surface writing step S64.

  In the first full-surface writing step S60, full-surface driving for drawing the entire display portion is performed. The first full-surface writing step S60 displays the second visual expression inside a given area of the display unit.

  For example, in the first full-surface writing step S60, the background of the 12 pixel × 12 pixel region (given region) is made black by full-surface driving, and the second visual expression is displayed in white there. Accordingly, the user can recognize that the display has shifted from the first visual expression to the second visual expression, and does not feel uncomfortable with the display.

  The reverse display partial erasing step S61 prevents the user from seeing an unnecessary display in the subsequent afterimage erasing symmetrization step S62. Specifically, by displaying the first fixed image in black by partial driving, the second visual representation displayed in white is erased, and the area of 12 pixels × 12 pixels is made black.

  The afterimage erasing symmetrization step S62 takes DC balance with the afterimage erasing step S24 using the second fixed image. For example, the afterimage erasing symmetrization step S62 achieves DC balance by displaying the second fixed image in black by the same partial drive as the afterimage erasing step S24. At this time, the area of 12 pixels × 12 pixels is black by the reverse display partial erasing step S61. Therefore, even if the fixed image is displayed in black, there is no possibility that it will be visually recognized by the user. Therefore, it is possible to achieve DC balance with the afterimage erasing step S24 without causing the user to misunderstand that it is a failure.

  When the afterimage erasing step S24 is repeated a given number of times (S4), it is necessary to balance the DC for all of them, and therefore the symmetrization process is also performed in the afterimage erasing symmetrization step S62. Repeatedly. For example, when the afterimage erasing step S24 is performed on the numbers 0 to 8 and the additional afterimage erasing step S26 is also performed, the second fixed image including the outlines of the numbers 0 to 8 is displayed in black. This process is repeated 10 times. In the afterimage erasing step S24 for the numeral 9, the first fixed image is used and symmetrized by the reverse display partial erasing step S61.

  In the second full-surface writing step S64, full-surface driving for drawing the entire display unit is performed. In the second full-surface writing step S64, the second visual expression is displayed inside a given area of the display unit. The display of the second visual expression at this time is the reverse display in the first full-surface writing step S60. For example, in the second full-surface writing step S64, the background of the 12 pixel × 12 pixel region (given region) is made white by full-surface driving, and the second visual expression is displayed in black there.

  The second full-surface writing step S64 is preferably DC balanced with the first full-surface writing step S60 as a whole. That is, it is preferable that the display by the second full-surface writing step S64 is a reverse display of the first full-surface writing step S60 not only in a given area but in the entire display unit.

  By following the driving method of the electrophoretic display device shown in the flowcharts of FIGS. 7, 8A, and 8B, the display is performed so as not to give the user a sense of incongruity (S60). By selectively using the fixed image and the second fixed image, an increase in processing steps can be suppressed, and a driving method of the electrophoretic display device that eliminates the afterimage of the contour portion with DC balance can be realized.

2. Electronic Timepiece An application example of the present invention to an electronic timepiece will be described with reference to FIGS. 9 and 11A to 11N. Comparative examples will be described with reference to FIGS. 10A to 10J. In addition, about the structure similar to FIGS. 1-8, the same code | symbol is attached | subjected and description is abbreviate | omitted and a different part is demonstrated.

  The electrophoretic display device 100 can be suitably applied to an electronic timepiece. At this time, the present invention can be widely applied without limiting types such as a wristwatch, a table clock, a wall clock, and a pocket watch.

  For example, FIG. 9 is a front view of a wrist watch 1000 that is one of electronic timepieces. The wristwatch 1000 includes a watch case 1002 and a pair of bands 1003 connected to the watch case 1002. A display unit 1004 including the electrophoretic display device 100 is provided in front of the watch case 1002, and the display unit 1004 displays a display 1005 including a time display. Two operation buttons 1011 and 1012 are provided on the side of the watch case. Note that various display forms such as time, calendar, and alarm may be selected as the display 1005 by the operation buttons 1011 and 1012.

2.1. Comparative Example Here, a display unit of an electronic timepiece which is an application example will be described in comparison with a comparative example. First, a comparative example will be described with reference to FIGS. 10 (A) to 10 (J). After that, application examples will be described with reference to FIGS.

  10A to 10J show display examples of the display unit 5 of the electronic timepiece according to the comparative example. The display unit 5 corresponds to the display unit 1004 in FIG. 9, but only the time display portion is extracted in FIGS. 10 (A) to 10 (J). An area 51 indicates an area where partial driving can be performed. In the display examples shown in FIGS. 10A to 10J, the area 51 corresponds to the first digit of the minute digit of the time display. For example, the area 51 may include the tenth digit of the minute digit, The entire time display may be the area 51.

  In the enlarged view (right figure) of the region 51 in FIG. 10A to FIG. 10J, a gray portion indicates a pixel that is not subject to partial driving. That is, the pixels displayed in black or white in the enlarged view of the region 51 are partially driven. In addition, although the process number attached | subjected to FIG. 10 (A)-FIG. 10 (J) respond | corresponds to the process number of the flowchart of FIG.7, FIG8 (A), FIG.8 (B), it is an additional afterimage in a comparative example. The erasing step S26 and the reverse display partial erasing step S61 are not included. In addition, the fixed image is not used in the afterimage erasing step and the afterimage erasing symmetrization step in the comparative example, and images used for each visual expression are different.

  FIG. 10A shows that the time is 12:00. The partial writing step S20 is performed, and 0 is displayed in black in the area 51 as a single digit.

  In FIG. 10B, before the time changes from 12:00 to 12:01, the partial erasing step S22 is performed, and the 0 displayed in black in the area 51 in FIG. 10A is erased. It shows that.

  FIG. 10C shows that the afterimage erasing step S24 is performed and the afterimage of the 0 contour portion displayed in black in the region 51 is erased. At this time, information on the contour forming pixels forming the 0 contour and the background boundary pixels is read from the storage unit 160. Then, afterimage erasure is performed by displaying an image including the contour forming pixels and the background boundary pixels for 0 in white.

  Thereafter, the first digit of the minute digit changes to 1, 2, 3,..., And the same steps as those in FIGS. 10 (D) to 10 (F) are cases where the first digit of the minute digit is 9 in FIGS. 10 (A) to 10 (C), respectively, and thus description thereof is omitted.

  FIG. 10G shows that the first full-surface writing step S60 is performed and the region 51 is displayed in black. At this time, the hour digit, the separator (:), and the ten digit of the minute digit may be displayed in white, but normal time display is not performed.

  FIG. 10H is a diagram showing that the afterimage erasing symmetrization step S62 is performed with respect to the afterimage erasing step S24 of FIG. In FIG. 10H, for example, the controller 63 reads out the information of the contour forming pixel of 0 which is the first digit of the minute digit and the background boundary pixel from the storage unit 160, displays the image including these in black, and performs DC balance. Take. Thereafter, the first digit of the minute digit is changed to 1, 2, 3,..., And the same process is repeated until 9 is reached (FIG. 10H to FIG. 10I). At this time, the controller 63 needs to read information such as a unique contour forming pixel corresponding to the first digit of the minute digit from the storage unit 160. That is, in the electronic timepiece of the comparative example, it is necessary to access the storage unit 160 ten times, which may cause a decrease in response speed and an increase in power consumption. Note that FIG. 10I performs the same processing as FIG.

  FIG. 10J shows that the second full-surface writing step S64 is performed and the region 51 is displayed in white. At this time, the display in FIG. 10J is the reverse of the display in FIG. 10G so that the display in FIG. 10G can be DC balanced.

  In this comparative example, DC balance is taken. However, the comparative example includes the following problems. First, the first full-surface writing step S60 in FIG. 10G is performed at a timing when the display changes from 9 to 0, and a normal clock display is performed between FIGS. 10G to 10J. It will never be. For this reason, when the minute digit changes, black display is generated and continues for a certain period of time, so that the user cannot see the expected change and may feel uncomfortable in the display. In addition, since it is necessary to acquire the image signal by accessing the storage unit 160 ten times in the afterimage elimination symmetrization step S62 of FIGS. 10H to 10I, the response speed of the electrophoretic display device is reduced. There is a possibility of increasing power consumption.

2.2. Application Example FIGS. 11A to 11N show display examples of the display unit 5 for an electronic timepiece according to an application example of the first embodiment. In addition, about the completely same process as a comparative example (FIG. 10 (A)-FIG. 10 (J)), the number of a corresponding drawing is described and description is abbreviate | omitted. Further, the same elements as those in FIGS. 10A to 10J are denoted by the same reference numerals, and description thereof is omitted. And in the right figure of Drawing 11 (A)-Drawing 11 (N), 1 or 2 surrounded by a circle represents that the 1st fixed picture and the 2nd fixed picture are used, respectively.

  11 (A) to 11 (B) are the same steps as FIGS. 10 (A) to 10 (B), respectively.

  FIG. 11C shows that the afterimage erasing step S24 is performed and the afterimage of the 0 contour portion displayed in black in the region 51 is erased. At this time, the second fixed image is used for afterimage erasure, and the information is read out from the storage unit 160 (see FIG. 1) as an image signal. The second fixed image is, for example, an image (see FIG. 6D) in which contour forming pixels with numbers 0 to 8 and background boundary pixels are combined.

  FIG. 11 (D) shows that the afterimage of the 0 contour portion displayed in black in the region 51 is erased again by the additional afterimage erasing step S26. In this application example, since 0 is the second visual expression, the additional afterimage erasing step S26 is performed. In this application example, 0 is displayed in black in the second full-surface writing step S64 (FIG. 11N) separately from the partial writing step S20 (FIG. 11A). Therefore, 0 is overwritten, and the outline portion is emphasized. Therefore, an additional afterimage erasing step S26 is performed for reliable afterimage erasure.

  Thereafter, the first digit of the minute digit changes to 1, 2, 3,..., And the same steps as those in FIGS. Note that FIG. 11E and FIG. 11F are the same steps as FIG. 11A and FIG.

  FIG. 11G to FIG. 11I show steps when the first digit of the minute digit is 9. Here, 9 is the first visual expression. 11G and 11H are the same steps as FIGS. 11A and 11B, respectively, and thus description thereof is omitted.

  FIG. 11I shows that the afterimage erasing step S24 is performed and the afterimage of the nine contour portions displayed in black in the region 51 is erased. At this time, not the second fixed image but the first fixed image is used for afterimage erasure, and the information is read out from the storage unit 160 (see FIG. 1) as an image signal. The first fixed image is an image obtained by combining numbers 9 and 0 (see FIG. 6F). Therefore, it does not include background boundary pixels and is not optimal for the purpose of erasing afterimages along the contour. However, since the entire surface of the display unit 5 is rewritten in the subsequent first full surface writing step S <b> 60, the afterimage here is not displayed on the display unit 5 for a long time. Therefore, the main purpose of the afterimage erasing step S24 for 9 (first visual expression) is to achieve DC balance with the reverse display partial erasing step S61 that follows the erasing of the afterimage.

  FIG. 11J shows that the first full-surface writing step S60 is performed, and 0 (second visual expression) is displayed in white in the region 51 by full-surface driving. At this time, the hour digit, the separator (:), and the ten-digit minute digits are also displayed in white, and normal display is performed. Since full-surface driving is performed, the region 51 in the right figure representing the target of partial driving is shown in gray.

  FIG. 11K shows that the reverse display partial erasing step S61 is performed, and 0 displayed in white in the region 51 is erased. At this time, the first fixed image is used for the afterimage erasing, and is DC balanced with the afterimage erasing step S24 of FIG. The first fixed image is an image obtained by combining numbers 9 and 0 (see FIG. 6F). Therefore, displaying the first fixed image in black causes the white 0 to be erased.

  FIG. 11L is a diagram showing that afterimage erasing symmetrization step S62 is performed in order to achieve DC balance with the afterimage erasing step S24 of FIG. 11C. For example, the controller 63 (see FIG. 1) reads the information of the second fixed image from the storage unit 160 and displays it in black symmetrically with FIG. In FIG. 11K, the entire area 51 is displayed in black as the background color, so that the display by the afterimage erasing symmetrization step S62 is not visually recognized by the user. That is, since the fixed image is displayed in black with respect to the black background color, it is not noticeable.

  Thereafter, in response to the change of the first digit of the minute digit to 0 (additional afterimage erasing step S26), 1, 2, 3,..., 8, the same processing as FIG. Repeated (FIG. 11 (L) to FIG. 11 (M)). In the afterimage erasing symmetrization step S62, even when the plurality of afterimage erasing steps S24 and the additional afterimage erasing step S26 are performed, the symmetrization processing can be performed collectively and efficiency can be improved. it can. At this time, since only two types of fixed images are used, the information of the fixed images need only be read twice from the storage unit 160. Therefore, the response speed is not reduced and the power consumption is not increased by accessing the storage unit 160. Note that FIG. 11M performs the same processing as FIG. 11L, and a description thereof is omitted.

  FIG. 11N shows that the second entire writing step S64 is performed and 0 is displayed in black in the region 51 by the entire driving. At this time, the display in FIG. 11N is obtained by inverting the display in FIG. 11J so that the display in FIG. 11J can be DC balanced.

  11A to 11N, for example, FIG. 11A and FIG. 11B, FIG. 11G and FIG. 11H, and FIG. 11B. As shown in FIG. 11K, the DC balance is taken, and the DC balance is taken as a whole.

  Here, in the electronic timepiece according to the application example, the timing at which the display is rewritten by full drive is the update timing of the minute digits, and the current time is displayed together with the reverse display as shown in FIG. Absent. Therefore, the problem that the user in the comparative example feels uncomfortable with the display is solved.

  Further, in the electronic timepiece according to the application example, the second fixed image is displayed in the afterimage erasing step S24, the additional afterimage erasing step S26, and the afterimage erasing symmetrization step S62 other than the first visual expression. In the afterimage erasing step S24 and the reverse display partial erasing step S61, the first fixed image is used. Since only two types of fixed images are used in the steps of FIGS. 11K to 11M, the information on the fixed images need only be read from the storage unit 160 twice. Therefore, problems such as a decrease in response speed and an increase in power consumption due to frequent access to the storage unit 160 in the comparative example are solved. Further, only three processing steps are added as compared with the comparative example.

  As described above, in the electronic timepiece according to the application example, the first fixed image and the second fixed image are selectively used while performing a display that does not give the user a sense of incongruity (FIG. 11J). An increase in processing steps is suppressed, and afterimage erasure is performed on a contoured portion with a DC balance without a decrease in response speed or an increase in power consumption.

3. Others In the above-described embodiment, the electrophoretic display device is not limited to one in which black and white two-particle electrophoresis is performed using black particles and white particles, and may perform one-particle electrophoresis such as blue and white, Also, combinations other than black and white may be used.

  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.

  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 5 ... Display part, 6 ... Control part, 20 ... Microcapsule, 26 ... Black particle, 27 ... White particle, 30 ... Element substrate, 31 ... Opposite substrate, 32 ... Electrophoretic element, 35 ... Pixel electrode, 35A ... Pixel electrode , 35B ... pixel electrode, 37 ... common electrode, 40 ... pixel, 40A ... pixel, 40B ... pixel, 40V ... pixel, 40W ... pixel, 40X ... pixel, 40Y ... pixel, 41 ... driving TFT (Thin Film Transistor), 49 ... Low potential power line (Vss), 50 ... High potential power line (Vdd), 51 ... Area, 55 ... Common electrode wiring (Vcom), 61 ... Scanning line driving circuit, 62 ... Data line driving circuit, 63 ... Controller , 64 ... common power supply modulation circuit, 66 ... scanning line, 68 ... data line, 70 ... latch circuit, 80 ... switch circuit, 91 ... first pulse signal line (S ₁ ), 92 ... second pulse signal line ( S ₂₎ DESCRIPTION OF SYMBOLS 100 ... Electrophoretic display apparatus, 160 ... Memory | storage part, 350 ... Drive electrode layer, 360 ... Electrophoretic display layer, 370 ... Common electrode layer, 1000 ... Wristwatch, 1002 ... Watch case, 1003 ... Band, 1004 ... Display part, 1005 ... Display, 1011 ... Operation button, 1012 ... Operation button

Claims (7)

A method for driving an electrophoretic display device including an electrophoretic element including electrophoretic particles between a pair of substrates and including a display unit including pixels capable of displaying at least a first color and a second color,
A partial rewriting step of rewriting a given visual expression including at least a first visual expression and a second visual expression by applying a voltage to the electrophoretic element within a given area of the display unit When,
Removing the asymmetry of the voltage applied in the partial rewriting step after the partial rewriting step is repeated a given number of times,
The partial rewriting process includes
A partial writing step of displaying, in the first color, visual expression forming pixels that are pixels forming the given visual expression;
A partial erasing step of displaying the visual representation forming pixels in the second color;
An afterimage erasing step of displaying, in the second color, pixels constituting a fixed image within the given region;
An additional afterimage erasing step of performing the afterimage erasing step again when the given visual representation is the second visual representation;
If the given visual representation is the first visual representation, the first fixed image is used as the fixed image; otherwise, the second fixed image is used as the fixed image. And
The asymmetry elimination step includes
Followed by rewriting of the first visual representation in the partial rewriting step,
A first full-surface writing step of performing full-surface driving to apply a voltage to the electrophoretic element in all regions of the display unit and displaying the visual expression forming pixels of the second visual expression in the second color;
A reverse display partial erasing step of displaying pixels constituting the first fixed image in the first color after the first full-surface writing step;
After the reverse display partial erasing step, the pixels constituting the second fixed image are changed to the first color by the number of times that the pixels constituting the second fixed image are displayed in the second color in the partial rewriting step. The afterimage elimination symmetrization process, which repeats the process of displaying in
After the afterimage erasing symmetrization step, performing a whole surface drive, and displaying the visual expression forming pixels of the second visual expression in the first color, and a second full surface writing step,
The method for driving an electrophoretic display device, wherein the partial rewriting step is performed again after the second full surface writing step. The method for driving an electrophoretic display device according to claim 1,
An electrophoretic display device driving method, wherein an image obtained by synthesizing the first visual expression and the second visual expression is used as the first fixed image. The method for driving an electrophoretic display device according to claim 1,
The method for driving an electrophoretic display device, wherein the given number of times is a plurality of times. An electrophoretic display device comprising:
A display unit including an electrophoretic element including electrophoretic particles between a pair of substrates and a pixel that can display at least a first color and a second color;
A control unit for controlling the display unit,
The controller is
Partial rewrite control for rewriting a given visual expression including at least a first visual expression and a second visual expression by applying a voltage to the electrophoretic element within a given area of the display unit When,
After the partial rewrite control is repeated a given number of times, the asymmetry elimination control for eliminating the asymmetry of the voltage applied in the partial rewrite control is performed,
In the partial rewrite control,
Partial writing control for displaying visual representation forming pixels that are pixels forming the given visual representation in the first color;
Partial erasure control for displaying the visual expression forming pixels in the second color;
An afterimage erasing control for displaying pixels constituting a fixed image in the given region in the second color;
Performing the afterimage removal control again when the given visual representation is the second visual representation, and performing an afterimage removal control,
If the given visual representation is the first visual representation, the first fixed image is used as the fixed image; otherwise, the second fixed image is used as the fixed image. And
In the asymmetry elimination control that is subsequently performed after the first visual expression is rewritten in the partial rewriting control,
A first full-surface writing control for performing full-surface driving for applying a voltage to the electrophoretic element in all regions of the display unit and displaying the visual expression forming pixels of the second visual expression in the second color;
Inversion display partial erasure control for displaying pixels constituting the first fixed image in the first color after the first full-surface writing control;
After the reverse display partial erasure control, the pixels constituting the second fixed image are changed to the first color as many times as the pixels constituting the second fixed image are displayed in the second color by the partial rewrite control. Afterimage symmetrization control that repeats the process of displaying in
After the afterimage erasing symmetrization control, performing the entire surface drive, performing a second entire surface writing control for displaying the visual expression forming pixels of the second visual expression in the first color,
An electrophoretic display device that performs the partial rewrite control again after the second full-surface write control. The electrophoretic display device according to claim 4.
The controller is
An electrophoretic display device, wherein an image obtained by combining the first visual expression and the second visual expression is used as the first fixed image. An electronic timepiece including the electrophoretic display device according to claim 4,
The display unit
At least display the time including the hour and minute digits,
The controller is
In the partial rewriting control, an electronic timepiece in which the minute digit of the time display is the given visual expression. The electronic timepiece according to claim 6,
The controller is
The afterimage erasing symmetrization control is performed once every 10 minutes,
The controller is
An electronic timepiece in which the first visual expression is 9 and the second visual expression is 0.