JPWO2007116448A1 - Display element driving method and display device - Google Patents

Abstract

The display element driving method includes a plurality of scan electrodes and a plurality of data electrodes that intersect each other in a state of being opposed to each other, and the scan electrodes are selected in a predetermined order to be displayed on a display medium between the scan electrodes and the data electrodes. The image rewriting process of the display screen is performed by applying a pulse voltage. In the image rewriting process, when a reset pulse for initializing the display medium and a rewrite pulse for rewriting the display medium according to image data are continuously applied to perform partial rewriting on an existing display image, The scan direction is switched according to the position of the partial rewrite area on the display screen.

Description

  The present invention relates to a display element driving method and a display device, and more particularly to a display element driving technique for still image display including cholesteric liquid crystal.

  In recent years, development of electronic paper has been actively promoted in research institutions such as companies and universities. As an application market in which electronic paper is expected, various application forms such as a sub display of a mobile terminal and a display unit of an IC card have been proposed, starting with an electronic book.

  Conventionally, a cholesteric liquid crystal is known as a leading electronic paper. This cholesteric liquid crystal has excellent characteristics such as semi-permanent display retention (memory property), vivid color display, high contrast and high resolution. Furthermore, the cholesteric liquid crystal can display a vivid full color by laminating display layers exhibiting RGB reflection colors.

  Cholesteric liquid crystals are sometimes referred to as chiral nematic liquid crystals. By adding a relatively large amount (several tens of percent) of chiral additives (also called chiral materials) to nematic liquid crystals, It is a liquid crystal whose molecules form a helical cholesteric phase.

  By the way, since the cholesteric liquid crystal is a liquid crystal having a memory property, an inexpensive simple matrix drive is possible, and for example, an enlargement of A4 size or larger is relatively easy. The cholesteric liquid crystal consumes power only when the display content is updated (image rewriting), and when the image rewriting is completed, the image is held as it is even if the power is turned off.

  First, an example of driving a cholesteric liquid crystal as an example of a display element according to the present invention will be described.

  1A and 1B are diagrams for explaining the alignment state of the cholesteric liquid crystal. FIG. 1A shows a planar state, and FIG. 1B shows a focal conic state.

  A cholesteric liquid crystal can take two stable states, a planar state and a focal conic state, under no electric field.

  That is, as shown in FIG. 1A, since the incident light is reflected by the liquid crystal in the planar state, the human eye can see the reflected light.

  Further, as shown in FIG. 1B, in the focal conic state, incident light passes through the liquid crystal. Then, by providing a light absorption layer separately from the liquid crystal layer, black can be displayed in the focal conic state.

  Here, in the planar state, light having a wavelength corresponding to the helical pitch of the liquid crystal molecules is reflected, and the wavelength λ at which the reflection is maximized is λ = when the average refractive index of the liquid crystal is n and the helical pitch is p. It is indicated by n · p. The reflection band Δλ increases with the refractive index anisotropy Δn of the liquid crystal. By selecting the average refractive index n of the liquid crystal and the helical pitch p, the color of the wavelength λ can be displayed in the planar state.

  2A, 2B, and 2C are diagrams showing voltage characteristics (relationship between time and voltage) for driving the cholesteric liquid crystal. The electric field applied to the liquid crystal and each homeotropic state, focal conic state, and planar state are shown. It shows the state of change. Here, the homeotropic state is H, the focal conic state is FC, and the planar state is P.

  First, when a strong electric field is applied to the cholesteric liquid crystal, the helical structure of the liquid crystal molecules is completely unwound, and all molecules enter a homeotropic state H according to the direction of the electric field.

  As shown in FIG. 2B, when the electric field is suddenly reduced to zero from the homeotropic state H, the spiral axis of the liquid crystal becomes perpendicular to the electrode, and the planar state P in which light is selectively reflected according to the spiral pitch is obtained.

  On the other hand, as shown in FIG. 2A, when the electric field is removed after the formation of a weak electric field that can finally unwind the liquid crystal molecules, or as shown in FIG. When removed, the spiral axis of the liquid crystal is parallel to the electrode, resulting in a focal conic state FC that transmits incident light.

  Further, if an electric field having an intermediate strength is applied and removed rapidly, the liquid crystal in the planar state P and the focal conic state FC is mixed, and halftone display becomes possible.

  Thus, the cholesteric liquid crystal is bistable, and information can be displayed using this phenomenon.

  FIG. 3 is a diagram showing the reflectance characteristics (the relationship between the voltage and the reflectance) of the cholesteric liquid crystal, and collectively shows the voltage responsiveness of the cholesteric liquid crystal described with reference to FIGS. 2A to 2C.

  As shown in FIG. 3, when the initial state is the planar state P (the portion with the high reflectivity at the left end in FIG. 3), when the pulse voltage is raised to a certain range, the driving band for the focal conic state FC is obtained, and further the pulse When the voltage is increased, the driving band for the planar state P (the high voltage portion at the right end) is reached again.

  When the initial state is the focal conic state FC (the leftmost portion having a low reflectance), the driving band for the planar state P is gradually increased as the pulse voltage is increased.

  In the planar state P, only the right circularly polarized light or the left circularly polarized light is reflected, and the remaining circularly polarized light is transmitted. Therefore, the theoretical maximum reflectance is 50%.

  Conventionally, a driving method of a liquid crystal display element that displays information by selecting a planar state and a focal conic state has been proposed in which a display element is quickly operated by phase transition driving in a fast-forward mode (for example, Patent Document 1). reference).

  Conventionally, as a method of driving a display element in a display device using a cholesteric liquid crystal, reset is performed with a predetermined number of scan lines before an image is actually written, and writing is performed after a pause is provided. A sequence has been proposed (see, for example, Patent Document 2). The prior art described in Patent Document 2 and its problems will be described in detail later.

JP 2000-171837 A International Publication No. 2005/024774 pamphlet (FIGS. 55 and 56 and Example 4)

  As described above, in recent years, electronic paper is being put into practical use using, for example, cholesteric liquid crystal. By the way, in the electronic paper, for example, a rewriting function (partial rewriting function) is required only for a specific area in the display area.

  The present applicant has filed a patent application relating to a driving method of a liquid crystal display element capable of rewriting a partial screen at high speed (Japanese Patent Application No. 2005-099711).

  4A and 4B are diagrams for explaining an example of a driving method of a display element according to related technology proposed in Japanese Patent Application No. 2005-099711. 4A and 4B, reference numeral 100 is an original image (existing image), 121 is a driver IC (scan driver) on the scanning side, 122 is a driver IC (data driver) on the data side, and 200 is after partial rewriting. An image and R0 indicate a partial rewrite area.

  In the original image 100 shown in FIG. 4A, when the partially rewritten region R0 is rewritten and the partially rewritten image 200 shown in FIG. 4B is displayed, in the related technique described above, as in the case of displaying a normal image. Instead of scanning all the scan-side areas (all scan electrodes) S10 at a normal speed and writing an image, for example, a scan-side area including the rewrite area R0 (a scan corresponding to the rewrite area R0) Electrode) Scans S12 at a normal speed to write (rewrite) an image, and scan-side area not including the rewrite area R0 (scan electrode not corresponding to the rewrite area R0: skip area) S11 and S13 at high speed It scans and maintains the original image.

  That is, in the scanning operation by the scan driver 121, first, the region S11 where partial rewriting is not performed is scanned in the high speed mode, and when reaching the region R0 where partial rewriting is performed, the image is rewritten by scanning at a normal scanning speed, and thereafter When the scan of the rewrite area R0 is completed, the area S13 where the partial rewrite is not performed is scanned in the high speed mode. This speeds up the processing operation for partial rewriting of the image.

  Here, it is most preferable to turn off the voltage output from the data driver 122 for the skip area (S11, S13) where rewriting is not performed so as not to affect the already written display image. However, since the response of the liquid crystal becomes dull by increasing the speed, it is possible to perform scanning without using this phenomenon to turn off the voltage output.

FIG. 5 is a diagram for explaining a shift in threshold characteristics due to high-speed scanning.
That is, in the high-speed mode in which the regions (S11, S13) before and after the rewrite region R0 are scanned, for example, a voltage of ± 24V or ± 32V is applied. For example, as shown in FIG. The threshold characteristics are greatly shifted (shifted to the higher potential side). Specifically, the operating threshold voltage of cholesteric liquid crystal is shifted to a high voltage of 32 V or higher. For example, even when a voltage of ± 24 V or ± 32 V is applied, the liquid crystal The orientation state (display state) does not change. Therefore, in the skip regions S11 and S13, the original image can be maintained as it is by simply scanning at high speed without turning off the voltage output.

  As described above, according to the related art display element driving method, when a part of the original image is partially rewritten, it is possible to speed up the rewriting process.

  By the way, for driving the cholesteric liquid crystal, it is preferable to apply a reset voltage before writing an actual image. The applicant of the present invention, as a conventional image writing method that consumes less power and achieves stable contrast, resets a predetermined number of scan lines before actually writing an image, and further pauses. In Japanese Patent Application Laid-Open No. 2004-228561, a writing sequence for performing writing after the provision of the above has been proposed.

  6A to 6C are diagrams for explaining an example of a conventional display element driving method proposed in the above-described prior art document 2. FIG. 6A to 6C, reference numeral 100 is a previous image (existing image), 121 is a common side driver IC (scan driver), 122 is a segment side driver IC (data driver), and 200 is a new image ( The image after rewriting) is shown. FIG. 6A shows a state where the lower half is rewritten with the previous image 100 and the upper half is rewritten with a new image 200. Further, in FIG. 6C, reference symbol Eio represents a common side selection signal for selecting a scan electrode for writing data line by line, and Lp represents one line corresponding to each scan electrode (scan line). The data-side latch / scan-side shift signal for sequentially taking in the data and shifting the scan line sequentially is shown.

  As shown in FIG. 6A to FIG. 6C, conventionally, for example, when image rewriting (writing) of cholesteric liquid crystal is performed, immediately before writing a new image, in the same frame as writing, the reset period RS → the pause period PS → It has been proposed to perform image writing in the sequence of the writing section WS. In FIG. 6A, reference numeral WT indicates a write head line in the write sequence, PL indicates a pause line, and RL indicates a reset line.

  Here, although the reset line RL (reset section RS) depends on the response characteristics of the liquid crystal, about 10 to 100 lines (for example, 20 lines) and the reset section WS (reset line RL) is about 50 to 100 msec. preferable. Note that the pause section PS (pause line) may be about one line.

  Since this conventional display element driving method is reset only for a specific number of lines, the power consumption is overwhelming compared to the case where the entire screen is reset at once, and stable contrast is achieved. High display can be obtained.

  However, the conventional display element driving method described above has problems to be solved as described below.

  7A and 7B are diagrams for explaining problems in an example of a conventional display element driving method. In FIG. 7B, reference symbol R0 indicates a partial rewrite area, S21 and S23 indicate areas where high-speed skip (high-speed skip processing) is performed, and S22 indicates areas where high-speed write (high-speed write processing) is performed. Is shown.

  As shown in FIG. 7A, the conventional display element driving method described above requires a predetermined number of reset lines RL (for example, about 20 lines: reset section RS) preceding the line to be actually written. For example, when rewriting a part of the display screen (rewrite area R0) as shown in FIG. 7B, when the write line reaches near the end of the rewrite area R0, the area Rz reset by the reset line RL becomes the rewrite area. It protrudes out of R0, and the display state of the original image without partial rewriting is impaired.

  On the other hand, although it is possible to perform partial rewriting without using the reset, for example, stable writing cannot be performed unless the partial rewriting speed is reduced to 20 msec./line or less. There is a risk that an afterimage of the display pattern before rewriting occurs due to the type and some temperature fluctuations and the like, resulting in unstable partial rewriting that does not reach the original contrast. In other words, in writing without reset processing, not only afterimages and contrast decrease before rewriting occurs, but it is difficult to rewrite unless the writing speed is significantly reduced. Some shortening of rewriting time was not to be demonstrated.

  In view of the problems of the conventional display element driving method described above, the present invention can realize stable partial rewriting without impairing image quality such as afterimage and contrast reduction in a driving method using a reset pulse. An object is to provide a display element driving method and a display device.

  According to the first aspect of the present invention, a plurality of scan electrodes and a plurality of data electrodes intersecting each other in an opposing state are provided, the scan electrodes are selected in a predetermined order, and each scan electrode and each data electrode are between A display element driving method for applying a pulsed voltage to the display medium to perform an image rewriting process on a display screen, the image rewriting process including a reset pulse for initializing the display medium, and the display medium When a rewrite pulse for rewriting the image in accordance with the image data is continuously applied to perform partial rewrite on the existing display image, the scan direction is switched according to the position of the partial rewrite area on the display screen. A display element driving method is provided.

  According to the second aspect of the present invention, a plurality of scan electrodes and a plurality of data electrodes intersecting each other in an opposing state are provided, the scan electrodes are selected in a predetermined order, and each scan electrode and each of the data electrodes are arranged. A display element driving method for applying a pulsed voltage to the display medium to perform an image rewriting process on a display screen, the image rewriting process including a reset pulse for initializing the display medium, and the display medium When a rewrite pulse for continuously rewriting the image according to the image data is applied continuously and a partial rewrite is performed on the existing display image, the reset pulse selects the start line or the end line of the partial rewrite region Provided is a display element driving method characterized in that the application time is longer than the time when the start line and the end line are not selected. .

  According to the third aspect of the present invention, a plurality of scan electrodes and a plurality of data electrodes intersecting each other in an opposing state are provided, the scan electrodes are selected in a predetermined order, and the scan electrodes and the data electrodes are arranged in a predetermined order. A display device having a display element that rewrites an image on a display screen by applying a pulsed voltage to the display medium, a scan driver connected to the scan electrode, and a data driver connected to the data electrode. A reset pulse for initializing the display medium, an image rewrite processing unit that continuously applies a rewrite pulse for rewriting the display medium according to image data, and a partial rewrite in an existing display image, A scan direction switching unit that switches a scan direction according to the position of the partial rewrite area on the display screen. A display device is provided.

  According to the fourth aspect of the present invention, a plurality of scan electrodes and a plurality of data electrodes intersecting each other in an opposed state are provided, the scan electrodes are selected in a predetermined order, and the scan electrodes and the data electrodes are arranged. A display device having a display element that rewrites an image on a display screen by applying a pulsed voltage to the display medium, a scan driver connected to the scan electrode, and a data driver connected to the data electrode. A reset pulse for initializing the display medium, an image rewrite processing unit that continuously applies a rewrite pulse for rewriting the display medium according to image data, and a partial rewrite in an existing display image, The reset pulse indicates a time during which the start line or the end line of the partial rewrite area is selected. Display apparatus is provided, characterized in that it comprises a processing unit for a longer application time than the time you do not select lines, a.

  According to the fifth aspect of the present invention, a plurality of scan electrodes and a plurality of data electrodes intersecting each other in an opposing state are provided, and the scan electrodes are selected in a predetermined order, and between the scan electrodes and the data electrodes. A display device having a display element that rewrites an image on a display screen by applying a pulsed voltage to the display medium, a scan driver connected to the scan electrode, and a data driver connected to the data electrode. A reset pulse for initializing the display medium, an image rewrite processing unit that continuously applies a rewrite pulse for rewriting the display medium according to image data, and a partial rewrite in an existing display image, A display device comprising: a scan direction switching unit that switches a scan direction in accordance with a position of the partial rewrite area on the display screen. Electronic terminal, characterized in that the applied is provided.

  According to the sixth aspect of the present invention, a plurality of scan electrodes and a plurality of data electrodes intersecting each other in an opposing state are provided, the scan electrodes are selected in a predetermined order, and the scan electrodes and the data electrodes are arranged. A display device having a display element that rewrites an image on a display screen by applying a pulsed voltage to the display medium, a scan driver connected to the scan electrode, and a data driver connected to the data electrode. A reset pulse for initializing the display medium, an image rewrite processing unit that continuously applies a rewrite pulse for rewriting the display medium according to image data, and a partial rewrite in an existing display image, The reset pulse indicates a time during which the start line or the end line of the partial rewrite area is selected. Electronic terminal, wherein the processing unit for a longer application time than the time you do not select line, that of applying a display device comprising a are provided.

  According to the present invention, it is possible to provide a display element driving method and a display device capable of realizing stable partial rewriting without impairing image quality in a driving method using a reset pulse.

It is FIG. (1) for demonstrating the orientation state of a cholesteric liquid crystal. FIG. 3 is a diagram (part 2) for explaining the alignment state of the cholesteric liquid crystal. FIG. 3 is a diagram (part 1) illustrating voltage characteristics for driving a cholesteric liquid crystal. FIG. 6 is a diagram (part 2) illustrating voltage characteristics for driving a cholesteric liquid crystal. FIG. 6 is a diagram (part 3) illustrating voltage characteristics for driving a cholesteric liquid crystal. It is a figure which shows the reflectance characteristic of a cholesteric liquid crystal. It is FIG. (1) for demonstrating an example of the drive method of the display element of related technology. It is FIG. (2) for demonstrating an example of the drive method of the display element of related technology. It is a figure for demonstrating the shift of the threshold characteristic by a high-speed scan. It is FIG. (1) for demonstrating an example of the driving method of the conventional display element. It is FIG. (2) for demonstrating an example of the driving method of the conventional display element. It is FIG. (3) for demonstrating an example of the driving method of the conventional display element. It is FIG. (1) for demonstrating the subject in an example of the driving method of the conventional display element. It is FIG. (2) for demonstrating the subject in an example of the driving method of the conventional display element. It is FIG. (1) for demonstrating the principle of the 1st form in the drive method of the display element which concerns on this invention. FIG. 6 is a diagram (No. 2) for explaining the principle of the first embodiment in the display element driving method according to the present invention; FIG. 6 is a diagram (No. 1) for explaining the allocation of the image memory according to the scan direction in an example of the display element driving method according to the invention. FIG. 10 is a diagram (No. 2) for explaining the allocation of the image memory according to the scan direction in the example of the display element driving method according to the invention. 1 is a block diagram schematically showing a first embodiment of a display device according to the present invention. It is sectional drawing which shows roughly an example of the display element in the display apparatus shown in FIG. It is a figure for demonstrating one Example of the drive method of the display element which concerns on this invention. It is a figure for demonstrating the modification of the drive method of the display element shown to FIG. 12A. It is a flowchart (the 1) for demonstrating one Example of the drive method of the display element which concerns on this invention. It is a flowchart (the 2) for demonstrating one Example of the drive method of the display element which concerns on this invention. It is a flowchart (the 3) for demonstrating one Example of the drive method of the display element which concerns on this invention. It is FIG. (1) for demonstrating the other Example of the drive method of the display element which concerns on this invention. It is FIG. (2) for demonstrating the other Example of the drive method of the display element which concerns on this invention. It is FIG. (1) for demonstrating the further another Example of the drive method of the display element which concerns on this invention. It is FIG. (2) for demonstrating other Example of the drive method of the display element which concerns on this invention. It is a figure which shows typically the principal part of 2nd Example of the display apparatus which concerns on this invention. It is a figure which shows typically the principal part of 3rd Example of the display apparatus which concerns on this invention. It is a figure which shows an example of the input voltage to the driver in a scan mode and a data mode. It is a figure which shows an example of a response | compatibility in the case of driving a cholesteric liquid crystal. It is a figure which shows an example of the output voltage of the driver in a scan mode and a data mode. It is a figure which shows an example of the synthetic | combination waveform applied to a liquid crystal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Display element 3 Power supply circuit 4 Control circuit 11, 12 Film board | substrate 13, 14 Transparent electrode (ITO)
15 Liquid crystal composition (cholesteric liquid crystal)
16, 17 Seal material 18 Light absorption layer 19 Drive circuit 21; 211, 212, 213, 214; 2101, 1022, 2103 Scan driver IC (scan driver)
22; 221, 222, 223, 224; 2201, 2202, 2203 Data driver IC (data driver)
31 Booster 32 Voltage generator 33 Regulator 41 Partial rewrite input unit 42 Image data generator 43 Position information generator 44 Data conversion circuit (image rewrite processor / scan direction switching unit)
100 Original image (existing image)
101 Blue (B) layer 102 Green (G) layer 103 Red (R) layer 121 Driver IC (scan driver) on the scanning side
122 Data side driver IC (data driver)
200 Image after partial rewriting FC Focal conic state H Homeotropic state P Planar state R0, R1, R2, R3, R4 Partial rewriting area

First, the principle of the first embodiment of the display element driving method according to the present invention will be described.
8A and 8B are diagrams for explaining the principle of the first embodiment in the display element driving method according to the present invention.

  In the display element driving method according to the present invention, the partial rewriting is performed from the start point to the end of the display screen by applying the reset pulse and the writing pulse to the same frame in the same manner as the full rewriting.

  As shown in FIG. 8A, for example, when the position of the partial rewrite region R1 is in the lower part of the display screen 300, the scan direction is the direction from the top to the bottom (S31 → S32). As shown in FIG. 8B, for example, when the position of the partial rewrite region R1 is in the upper part in the display screen 300, the scan direction is a direction from bottom to top (S34 → S33). Here, reference numerals S31 and S34 indicate areas where high-speed skip processing is performed, and S32 and S33 indicate areas where high-speed writing is performed.

  9A and 9B are diagrams for explaining image memory allocation according to a scan direction in an example of a display element driving method according to the present invention.

  As shown in FIG. 9A, for example, when the partial rewrite area R11 “Tomorrow's weather is fine” is located in the lower part of the display screen 301, the scanning direction is a direction from top to bottom. At this time, the data driver 22 receives, for example, data that is normally read from the image data in the partial rewrite area R11 stored in the memory in order from the top, that is, data that is read with the upper left of the image data as address 0. Transferred.

  On the other hand, as shown in FIG. 9B, for example, when the partial rewrite area R11 “Tomorrow's weather is fine” is located in the upper part of the display screen 301, the scan direction is from the bottom to the top. Become. At this time, for example, the data read out from the lower part of the image data in the partial rewrite area R11 stored in the memory, that is, the data read out with the lower left of the image data as the address 0 is transferred to the data driver 22, for example. Is done.

  In this way, the access procedure for the address of the image data in the partial rewrite area R11 is also switched according to the switching of the scanning direction.

  As described above, according to the present invention, it is possible to prevent the loss of display other than the rewrite region R1 due to the protrusion of the reset line described above, and it is possible to realize stable partial rewrite without an afterimage or contrast reduction. Become.

  Hereinafter, embodiments of a display element driving method and a display device according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 10 is a block diagram schematically showing a first embodiment of a display device (electronic terminal) according to the present invention. In FIG. 10, reference numeral 1 is a display element, 3 is a power supply circuit, 4 is a control circuit, 5 is an inverter, 21 is a scan driver IC (scan driver), and 22 is a data driver IC (data driver). .

  As shown in FIG. 10, the power supply circuit 3 includes a booster 31, a display element drive voltage generator (voltage generator) 32, and a regulator 33. For example, the booster 31 receives an input voltage of about +3 to +5 V from the battery, boosts the voltage to drive the display medium (display element 1), and supplies the boosted voltage to the voltage generator 32. The voltage generation unit 32 generates necessary voltages for the scan driver 21 and the data driver 22 respectively, and the regulator 33 stabilizes the voltage from the voltage generation unit 32 and supplies it to the scan driver 21 and the data driver 22. .

  The control circuit 4 includes a partial rewrite input unit 41, an image data generation unit 42, a position information generation unit 43, and a data conversion circuit 44. The control circuit 4 calculates image data and control signals supplied from the outside, and when an image pattern to be partially rewritten and a position in the display screen to input it are input, the data conversion circuit 44 responds to the information. The scanning direction of the scan driver 21 is determined, and image data input to the driver 21 is rearranged as necessary.

  That is, the partial rewriting input unit 41 recognizes partial rewriting from image data and control signals supplied from the outside, generates image data of an area where partial rewriting is performed by the image data generation unit 42, and a position information generation unit 43. The position information of the area to be partially rewritten (position information in the display area of the rewrite area) is generated. The image data and position information of these rewrite areas are input to the data conversion circuit 44, and the scan direction signal CS1, the data capture clock CS2, the pulse polarity control signal CS3, and the frame start signal CS4 that determine the scan direction of the scan driver 21 described above. , A data latch / scan shift signal CS5 and a driver output cutoff signal CS6 are output.

  Here, the data capture clock CS2 is supplied to the driver set in the data mode, and is a signal for sequentially capturing data for one line (in the case of partial rewriting, data in a region to be rewritten). The polarity control signal CS3 is a signal for inversion control of the polarity of the pulse voltage applied to the display element 1, the frame start signal CS4 is a signal indicating the start of an image of one frame, and the data latch / scan shift signal CS5. Is a signal for performing synchronous control of a line in which data is stored by the data driver and a line selected by the scan driver, and the driver output cutoff signal CS6 cuts off the driver output of the data driver or scan driver It is a signal for.

  In other words, when rewriting a partial area in an existing display image, if the rewritten area is in the lower part of the display screen, the scan direction is the direction from the top to the bottom of the display screen. If the rewriting area is in the upper part of the display screen, the scanning direction is the direction from the bottom to the top of the display screen. Note that the display element driving method according to the present invention will be described in detail later.

  11 is a cross-sectional view schematically showing an example of a display element (liquid crystal display element) in the display device shown in FIG. In FIG. 11, reference numerals 11 and 12 are film substrates, 13 and 14 are transparent electrodes (for example, ITO), 15 is a liquid crystal composition (cholesteric liquid crystal), 16 and 17 are sealing materials, 18 is a light absorbing layer, and Reference numeral 19 denotes a drive circuit.

  The display element 1 includes a liquid crystal composition 15, and transparent electrodes 13 and 14 that intersect perpendicularly are formed on the inner surfaces of the transparent film substrates 11 and 12 (surfaces in which the liquid crystal composition 15 is sealed), respectively. ing. That is, a plurality of scan electrodes 13 and a plurality of data electrodes 14 are formed in a matrix on opposing film substrates 11 and 12. In FIG. 11, the scan electrodes 13 and the data electrodes 14 are drawn so as to be parallel at first glance. However, actually, for example, a plurality of data electrodes 14 intersect one scan electrode 13. Needless to say. Furthermore, the thickness of each film substrate 11 and 12 is, for example, about 0.2 mm, and the thickness of the liquid crystal composition 15 is, for example, about 3 μm to 6 μm. Their ratio is ignored.

  Here, the electrodes 13 and 14 are preferably coated with an insulating thin film or an alignment stabilizing film. Further, a visible light absorption layer 18 is provided on the outer surface (back surface) of the substrate (12) opposite to the side on which light is incident, if necessary.

  In this example, the liquid crystal composition 15 is a cholesteric liquid crystal exhibiting a cholesteric phase at room temperature, and these materials and combinations thereof will be specifically described by the following experimental examples.

  The sealing materials 16 and 17 are for sealing the liquid crystal composition 15 between the film substrates 11 and 12. The drive circuit 19 is for applying a predetermined pulse voltage to the electrodes 13 and 14.

  Although the film substrates 11 and 12 both have translucency, at least one of the pair of substrates that can be used as the display element 1 of this embodiment needs to have translucency. It is. In addition, although a glass substrate can be illustrated as a board | substrate which has translucency, flexible resin film substrates, such as PET and PC, can be used besides a glass substrate. In addition, as the electrodes 13 and 14, for example, ITO (Indium Tin Oxide) is representative, but in addition, for example, a transparent conductive film such as IZO (Indium Zinc Oxide). Alternatively, a metal electrode such as aluminum or silicon, or a photoconductive film such as amorphous silicon or BSO (Bismuth Silicon Oxide) can be used.

  In the liquid crystal display element shown in FIG. 11, as described above, a plurality of strip-like transparent electrodes 13 and 14 parallel to each other are formed on the inner surfaces of the transparent film substrates 11 and 12, and these electrodes 13 and 14 are formed on the substrate. They face each other so as to intersect each other when viewed from a direction perpendicular to the direction.

  In the display element according to the present invention, an insulating thin film having a function of preventing a short circuit between the electrodes or improving the reliability of the liquid crystal display element as a gas barrier layer may be formed. Examples of the orientation stabilizing film include organic films such as polyimide resin, polyamideimide resin, polyetherimide resin, polyvinyl butyral resin, and acrylic resin, or inorganic materials such as silicon oxide and aluminum oxide. The alignment stabilizing film coated on the electrodes 13 and 14 can also be used as an insulating thin film.

  The liquid crystal display element according to the present invention may be provided with a spacer between the pair of substrates for uniformly holding the inter-substrate gap. Examples of the spacer include F spheres made of resin or inorganic oxide. Further, a fixed spacer whose surface is coated with a thermoplastic resin can also be suitably used.

  The substance constituting the liquid crystal composition (liquid crystal layer) 15 is, for example, cholesteric liquid crystal obtained by adding 10 to 40 wt% of a chiral agent to the nematic liquid crystal composition. Here, the addition amount of the chiral agent is a value when the total amount of the nematic liquid crystal component and the chiral agent is 100 wt%.

  Various types of conventionally known nematic liquid crystals can be used as the nematic liquid crystal, but a dielectric anisotropy of 20 or more is preferable for the convenience of driving voltage. That is, when the dielectric anisotropy is 20 or more, the driving voltage is relatively low. The dielectric anisotropy (Δε) of the cholesteric liquid crystal composition is preferably 20-50. Within this range, general-purpose drivers can be used.

  The refractive index anisotropy (Δn) is preferably 0.18 to 0.24. If it is smaller than this range, the reflectivity in the planar state is lowered, and if it is larger than this range, the scattering reflection in the focal conic state is increased and the viscosity is increased and the response speed is lowered. The thickness of the liquid crystal is preferably about 3 μm to 6 μm. If the thickness is smaller than this, the planar reflectivity is lowered, and if it is larger, the driving voltage becomes too high.

  FIG. 12A is a diagram for explaining an embodiment of a display element driving method according to the present invention, and FIGS. 13A to 13C are diagrams for explaining an embodiment of a display element driving method according to the present invention. It is a flowchart of.

  In FIG. 12A, the common side (scan driver 21) is configured by two scan drivers 211 and 212. FIG. Note that the flowcharts shown in FIGS. 13A to 13C explain the operation when only two scan drivers shown in FIG. 12A are provided.

  First, in step ST1, partial rewrite conditions, that is, image data Example.dat (u, v) are set. In step ST2, the image data Example.dat (u, v) is stored in the memory. In step ST3, the rewrite position is stored in the memory. In step ST4, it is determined whether or not the position of the partial rewrite image (partial rewrite region R2) straddles the two scan drivers 211 and 212.

  If it is determined in step ST4 that the position of the partial rewrite region R2 crosses the two scan drivers 211 and 212, the process proceeds to step ST5, the partial scan is started by the first scan driver 211, and the process proceeds to step ST6. Here, when the position of the partial rewrite region R2 straddles the two scan drivers 211 and 212, it is a case where the rewrite region R2 is positioned below the display screen corresponding to the first scan driver 211. The scan direction 211 is a direction from the top to the bottom of the display screen. The scanning direction from the top to the bottom is determined in advance as the basic scanning direction.

  In step ST6, the first scan driver 211 performs high-speed skip processing of the region S41, and further proceeds to step ST14, where the first scan driver 211 writes the image to the region S42 corresponding to a part of the rewrite region R2. To start.

  Further, in step ST15, image data Example.dat (u, v) is input to the data driver 22. In this case, the memory access order is forward, and the coordinate data (0, 0), (1, 0), line of each line from which the image data Example.dat (u, v) stored in the memory is read. (2, 0), ..., (u-1, 0); (0, 1), (1, 1), (2, 1), ..., (u-1, 1); v−1), (1, v−1), (2, v−1),..., (u−1, v−1) are sequentially written in the data driver 22 corresponding to each scan line in the region S42. .

  Then, the process proceeds to step ST16, the voltage pulse output (32V or 24V) is applied to the corresponding data electrode, and the process proceeds to step ST17, where the writing by the first scan driver 211 is completed.

  Next, proceeding to step ST26, the scan direction of the second scan driver 212 is switched from the bottom to the top of the display screen opposite to the basic scan direction. Here, when the position of the partial rewrite region R2 crosses the two scan drivers 211 and 212, the rewrite region R2 is located above the display screen corresponding to the second scan driver 212, so the scan driver The scan direction 212 is a direction from the bottom to the top of the display screen.

  In step ST27, the second scan driver 212 performs high-speed skip processing of the area S44, and further proceeds to step ST28, in which the second scan driver 212 corresponds to a part of the rewrite area R2. Image writing to S43 is started.

  Further, in step ST29, image data Example.dat (u, v) is input to the data driver 22. In this case, the memory access order is in the upside down direction, and the image data stored in the memory Example.dat (u, v) is read out from the coordinate data (0, v−1), (1, v) of each line. -1), (2, v-1), ..., (u-1, v-1); (0, v-2), (1, v-2), (2, v-2), ..., (U-1, v-2); ...; (0, 0), (1, 0), (2, 0), ..., (u-1, 0) sequentially correspond to each scan line in the region S43. And write to the data driver 22.

  Then, the process proceeds to step ST30, the voltage pulse output (32V or 24V) is applied to the corresponding data electrode, the process proceeds to step ST31, the writing by the second scan driver 212 is terminated, and the process proceeds to step ST32. Then, the partial rewriting (writing of the rewriting area R2) is finished.

  On the other hand, when it is determined in step ST4 that the position of the partial rewrite area (R2) does not straddle the two scan drivers 211 and 212, that is, the partial rewrite area is included in the area of one scan driver. Proceeding to ST7, it is determined whether the partial rewrite area is included in the area of the first scan driver 211 or the area of the second scan driver 212, and the process proceeds to step ST8. In step ST8, whether or not the distance from the partial rewrite area to the data driver 22 is long, that is, the upper length from the partial rewrite area to the upper end of the display screen ≧ the lower length from the partial rewrite area to the lower end of the display screen Determine the thickness.

  If it is determined in step ST8 that the upper length ≧ the lower length, that is, in the first or second scan driver (scan driver including the rewrite area) that scans the area including the partial rewrite area. If it is determined that the partial rewrite area is below the display screen corresponding to the scan driver including the rewrite area, the process proceeds to step ST9 to start partial rewrite with the scan driver including the rewrite area, and to step ST10. move on.

  In step ST10, high-speed skip processing is performed by the scan driver including the rewrite area. Further, the process proceeds to step ST18, and image writing is started by the scan driver including the rewrite area. Further, the process proceeds to step ST19, where image data Example. dat (u, v) is input to the data driver 22. In this case, the memory access order is forward as in step ST15 described above.

  Then, the process proceeds to step ST20, the voltage pulse output (32V or 24V) is applied to the corresponding data electrode, the process proceeds to step ST21, the writing by the scan driver including the rewrite area is terminated, and the process proceeds to step ST32. Finish rewriting.

  If it is determined in step ST8 that the upper length is not greater than the lower length, that is, if the partial rewrite area is determined to be above the display screen corresponding to the scan driver including the rewrite area. Then, the process proceeds to step ST11, the scan direction of the scan driver including the rewrite area is switched from the bottom to the top of the display screen opposite to the basic scan direction, and the process proceeds to step ST12.

  In step ST12, partial rewriting is started with a scan driver including a rewriting area, the process proceeds to step ST13, and a high-speed skip process is performed by the scan driver including the rewriting area, and the process proceeds to step ST22, and the scan driver including the rewriting area is performed. To start image writing.

  In step ST23, the image data Example.dat (u, v) is input to the data driver 22. In this case, as in step ST29 described above, the memory access order is in the upside down direction.

  Then, the process proceeds to step ST24, the voltage pulse output (32V or 24V) is applied to the corresponding data electrode, the process proceeds to step ST25, the writing by the scan driver including the rewrite area is terminated, and the process proceeds to step ST32. Finish rewriting.

12B is a diagram for explaining a modification of the display element driving method shown in FIG. 12A.
In the above description, the common side as shown in FIG. 12A is constituted by two scan drivers 211 and 212, and the segment side is constituted by one data driver 22 provided at one end (upper end) of the display screen. Although the element has been described, for example, the common side as shown in FIG. 12B is configured by two scan drivers 211 and 212, and the segment side is provided with two data drivers provided at both ends (upper end and lower end) of the display screen. The present invention can be similarly applied to the display elements constituted by 221 and 222.

  Note that in the display element having the two scan drivers 211 and 212 as shown in FIG. 12B, the first write process by the first scan driver 211 and the first data driver 221 and the second scan driver 212 are performed. It is also possible to perform the second write processing by the second data driver 222 in parallel (simultaneously). That is, in the display element (display device) shown in FIG. 12B, the first scan driver 211 performs high-speed skip processing in the scan direction (downward) from the top to the bottom of the region S45 and the bottom of the region S48 by the second scan driver 212. High-speed skip processing in the scan direction (upward) from the top to the top at the same time, and the high-speed write processing in the downward direction of the region S46 by the first scan driver 211 and the high-speed write in the upward direction of the region S47 by the second scan driver 212 By simultaneously performing the processing, it is possible to further reduce the time required for partial rewriting.

  14A and 14B are diagrams for explaining another embodiment of the display element driving method according to the present invention.

  14A shows that the common side (scan driver 21) is composed of four scan drivers 211 to 214, and FIG. 14B is just that the common side is composed of four scan drivers 211 to 214 as in FIG. 14A. In addition, the segment side (data driver 22) is also composed of two data drivers 221 and 222 provided at the upper and lower ends of the display screen.

  Note that when the positional relationship between the first to fourth scan drivers 211 to 214 and the partially rewritten image (partially rewritten region R3) is as shown in FIG. 14A, for example, the first scan driver 211 sequentially changes the region S51. The downward high-speed skip processing, the downward high-speed skip processing of the region S52 by the second scan driver 212, the downward high-speed writing processing of the region S53 by the second scan driver 212, and the region S54 by the third scan driver 213 The downward high-speed writing process is performed, and then the upward high-speed skip process of the area S56 by the fourth scan driver 214 and the upward high-speed writing process of the area S55 by the fourth scan driver 214 are performed.

  Further, when the positional relationship between the first to fourth scan drivers 211 to 214 and the partial rewrite region R3 is as shown in FIG. 14B, for example, the first scan driver 211 sequentially performs the downward high-speed skip processing in the region S61. And the fourth scan driver 214 simultaneously perform the upward high-speed skip process in the area S66, and the second scan driver 212 performs the downward high-speed skip process in the area S62 and the fourth scan driver 214 in the upward direction in the area S65. The high-speed writing process is simultaneously performed, and the downward high-speed writing process of the area S63 by the second scan driver 212 and the upward high-speed writing process of the area S64 by the third scan driver 213 are simultaneously performed.

  Thus, the number of common side scan drivers may be plural, and the number of segment side data drivers may be one at one end of the display screen or two at both ends of the display screen.

  For example, for some lines from the write start line for partial rewriting, a write pulse is directly applied without being given a reset pulse, or a predetermined display characteristic is not achieved because the number of lines to which a reset pulse is given is insufficient. It may not be obtained. Therefore, for example, it is preferable to apply the reset pulse in advance only to the line to which the reset pulse is not applied or to increase the pulse application time by reducing the scanning speed.

  Incidentally, as described above with reference to FIG. 7B and the like, in the conventional display element driving method, when a part of the display screen (rewrite region R0) is rewritten, the write line is close to the end of the rewrite region R0. When it reaches, the area Rz reset by the reset line RL protrudes outside the rewrite area R0, and the display state of the original image that is not partially rewritten is impaired. Further, when partial rewriting is performed without resetting, for example, the writing speed has to be greatly reduced, and the rewriting time, which is the original merit of partial rewriting, cannot be reduced.

  15A and 15B are views for explaining still another embodiment of the display element driving method according to the present invention.

  The display element driving method of this embodiment is characterized in that the reset period and the writing period are performed in different frames (frame division) at the time of partial rewriting.

  That is, as shown in FIG. 15A, first, in the first frame, for example, the high-speed skip processing of the region S71 is performed in the scan direction from top to bottom, and then the scan line corresponding to the partial rewrite region R4 ( The reset process of area S72) is performed, and the high-speed skip process of area S73 is further performed. Thereby, for example, in a display element using cholesteric liquid crystal, the region S72 corresponding to the partial rewrite region R4 is in a planar state.

  Then, in the next second frame, for example, high-speed skip processing of the region S71 is performed in the scan direction from top to bottom, and then high-speed writing processing of the rewritten image is performed in the region S72 corresponding to the partial rewrite region R4. Further, the high-speed skip process for the area S73 is performed.

  Note that while the partial rewrite region is scanned, the difference voltage between the scan electrode and the data electrode is set to be equal to or lower than the response value voltage of the display medium (for example, cholesteric liquid crystal).

  Thereby, it is possible to avoid the reset region (Rz) from protruding from the rewrite region. In addition, since the number of selected lines is limited in the reset period, an increase in power consumption can be suppressed.

  In this case as well, for example, the number of lines from the beginning of partial rewriting and the number of lines from before the end of writing may not be able to obtain predetermined display characteristics because the number of reset lines is insufficient at a constant scanning speed. . For this reason, when the reset pulse selects the start line and the end line of partial rewriting, it is effective to reduce the scan speed and increase the pulse application time to compensate for the reset effect. The reset time is the scan speed × the number of reset lines.

  In FIG. 16, reference numeral 101 is a blue (B) layer that reflects blue light, 102 is a green (G) layer that reflects green light, and 103 is a red (R) layer that reflects red light. Show. Note that a black (K) layer that absorbs light may be provided under the R layer 103.

  As shown in FIG. 16, the display device of the second embodiment has scan drivers 2101, 2102 and 2103, and data drivers 2201, 2202 and 2203 for the B layer 101, the G layer 102 and the R layer 103, respectively. 2203 is provided. In each of the layers 101, 102, and 103, scan electrodes and data that are connected to the scan drivers 2101, 2102, and 2103, and the data drivers 2201, 2202, and 2203 and intersect each other with the cholesteric liquid crystal (display medium) interposed therebetween. With the electrodes, the display element 1 can perform display close to full color.

FIG. 17 is a diagram schematically showing a main part of a third embodiment of the display device according to the present invention.
As shown in FIG. 17, the display device according to the third embodiment has a common scan driver 21 and individual data drivers 2201, 2202, and 2203 for the B layer 101, the G layer 102, and the R layer 103. Is provided.

  In this way, by sharing the scan driver between the B layer 101, the G layer 102, and the R layer 103, the number of drivers and the like can be reduced and the cost can be reduced.

  Hereinafter, the driving voltage of the QVGA color display device manufactured by applying the display device of the second embodiment shown in FIG. 16 will be described with reference to FIGS. 18A to 18D. Note that general-purpose STN drivers were used as the scan drivers 2101 to 2103 and the data drivers 2201 to 2203. Further, if necessary, a voltage follower of an operational amplifier may be applied to stabilize the voltage input to each driver.

  18A is a diagram illustrating an example of an input voltage to the driver in the scan mode and the data mode, FIG. 18B is a diagram illustrating an example of correspondence when driving the cholesteric liquid crystal, and FIG. 18C is an output voltage of the driver in the scan mode and the data mode. FIG. 18D is a diagram illustrating an example of a composite waveform applied to the liquid crystal.

  First, as shown in FIGS. 18A and 18B, in the data mode (segment mode: data driver), an arbitrary line can be selected. A high level “H” data signal can be selected with respect to a high level “H” data signal. As the AC signal, the voltage V0 (32V) and the low level “L” AC signal are the voltage V5 (0 V), and the low level “L” data signal is the high level “H” AC signal. The voltage V34 (4V) is used as the AC signal of the voltage V21 (28V) and the low level “L”.

  In scan mode (common mode: scan driver), any line cannot be selected. All lines are scanned, and a high level “H” data signal is a voltage as a high level “H” AC signal. The voltage V0 (32V) as an AC signal of V5 (0V) and low level “L”, and the voltage V21 (28V) as an AC signal of high level “H” with respect to a data signal of low level “L”. The voltage V34 (4V) is used as the low level “L” AC signal. Here, the relationship of V0 ≧ V21 ≧ V34 ≧ V5 is established.

  In each of the RGB elements (R layer 103, G layer 102, and B layer 101), a pulse voltage of ± 32V is stably applied to on pixels and ± 24V is applied to off pixels, and non-selected pixels are applied to non-selected pixels. A pulse voltage of ± 4 V is applied. That is, as shown in FIG. 18B, the scan driver (common driver: COM) and the data driver (segment driver: SEG) include, for example, 32V, 28V, 24V, 8V, generated by the power supply circuit 3 in FIG. Voltages of 6 levels of 4V and 0V are input.

  Therefore, 32V, 28V, 4V, and 0V are input to the scan mode driver, and 32V, 24V, 8V, and 0V are input to the data mode driver, and the scan mode and data mode of the driver are switched. Each voltage input to the drivers is also switched.

  As shown in FIG. 18C, the output voltage when the scan driver is turned on and off is 0V in the first half of the AC drive for the ON-COM and 32V in the second half, and 28V in the first half of the AC drive of the OFF-COM and the second half in the second half. The output voltage when the data driver is on and off is 32V in the first half of the AC drive for the ON-SEG and 0V in the second half, and 24V in the first half of the AC drive for the OFF-SEG and 24V in the second half. It is 8V.

  As shown in FIG. 18D, the liquid crystal (pixel) between each scan electrode and each data electrode has a pulse waveform of 32V for the first half AV11 of the AC drive and -32V for the second half AV21 for the liquid crystal selected on. The first half AV12 of AC driving is applied with a pulse waveform of 24V and the latter half AV22 is applied with a pulse waveform of −24V, and the first half AV13 of AC driving is 4V and the latter half of AV23 is applied to a non-selected ON liquid crystal. A pulse waveform of −4V is applied, and to the non-selection-off liquid crystal, a pulse waveform of −4V is applied to the first half AV14 of AC drive and 4V is applied to the second half AV24.

  An area where partial rewriting is performed is scanned at a speed of about 10 msec./line, for example, and a non-target area where partial rewriting is not performed is instantaneously scanned at a scanning speed of about μsec. / Line, for example. It will be. Note that when scanning non-target areas, it is preferable to turn off the voltage output from the driver, but if the voltage is below the voltage that the liquid crystal (pixel) responds to during high-speed scanning, the previous image will be maintained, which is problematic There is no.

  As described above, the present invention can be applied to, for example, a display element capable of full-color display in which the B layer 101, the G layer 102, and the R layer 103 are stacked, and an image to be partially rewritten (rewrite region) Full-color rewriting can be performed by rewriting all the layers. For example, only the G layer 102 can be rewritten.

  The present invention is not limited to cholesteric liquid crystals, and is widely applied to, for example, electronic devices using other liquid crystals that require reset processing before rewriting processing and electronic terminals having a display device using the same. Can do.

  The present invention relates to a display element driving method and a display device, and more particularly to a display element driving technique for still image display including cholesteric liquid crystal.

  In recent years, development of electronic paper has been actively promoted in research institutions such as companies and universities. As an application market in which electronic paper is expected, various application forms such as a sub display of a mobile terminal and a display unit of an IC card have been proposed, starting with an electronic book.

  Conventionally, a cholesteric liquid crystal is known as a leading electronic paper. This cholesteric liquid crystal has excellent characteristics such as semi-permanent display retention (memory property), vivid color display, high contrast and high resolution. Furthermore, the cholesteric liquid crystal can display a vivid full color by laminating display layers exhibiting RGB reflection colors.

  Cholesteric liquid crystals are sometimes referred to as chiral nematic liquid crystals. By adding a relatively large amount (several tens of percent) of chiral additives (also called chiral materials) to nematic liquid crystals, It is a liquid crystal whose molecules form a helical cholesteric phase.

  By the way, since the cholesteric liquid crystal is a liquid crystal having a memory property, an inexpensive simple matrix drive is possible, and for example, an enlargement of A4 size or larger is relatively easy. The cholesteric liquid crystal consumes power only when the display content is updated (image rewriting), and when the image rewriting is completed, the image is held as it is even if the power is turned off.

  First, an example of driving a cholesteric liquid crystal as an example of a display element according to the present invention will be described.

  1A and 1B are diagrams for explaining the alignment state of the cholesteric liquid crystal. FIG. 1A shows a planar state, and FIG. 1B shows a focal conic state.

  A cholesteric liquid crystal can take two stable states, a planar state and a focal conic state, under no electric field.

  That is, as shown in FIG. 1A, since the incident light is reflected by the liquid crystal in the planar state, the human eye can see the reflected light.

  Further, as shown in FIG. 1B, in the focal conic state, incident light passes through the liquid crystal. Then, by providing a light absorption layer separately from the liquid crystal layer, black can be displayed in the focal conic state.

  Here, in the planar state, light having a wavelength corresponding to the helical pitch of the liquid crystal molecules is reflected, and the wavelength λ at which the reflection is maximized is λ = when the average refractive index of the liquid crystal is n and the helical pitch is p. It is indicated by n · p. The reflection band Δλ increases with the refractive index anisotropy Δn of the liquid crystal. By selecting the average refractive index n of the liquid crystal and the helical pitch p, the color of the wavelength λ can be displayed in the planar state.

  2A, 2B, and 2C are diagrams showing voltage characteristics (relationship between time and voltage) for driving the cholesteric liquid crystal. The electric field applied to the liquid crystal and each homeotropic state, focal conic state, and planar state are shown. It shows the state of change. Here, the homeotropic state is H, the focal conic state is FC, and the planar state is P.

  First, when a strong electric field is applied to the cholesteric liquid crystal, the helical structure of the liquid crystal molecules is completely unwound, and all molecules enter a homeotropic state H according to the direction of the electric field.

  As shown in FIG. 2B, when the electric field is suddenly reduced to zero from the homeotropic state H, the spiral axis of the liquid crystal becomes perpendicular to the electrode, and the planar state P in which light is selectively reflected according to the spiral pitch is obtained.

  On the other hand, as shown in FIG. 2A, when the electric field is removed after the formation of a weak electric field that can finally unwind the liquid crystal molecules, or as shown in FIG. When removed, the spiral axis of the liquid crystal is parallel to the electrode, resulting in a focal conic state FC that transmits incident light.

  Further, if an electric field having an intermediate strength is applied and removed rapidly, the liquid crystal in the planar state P and the focal conic state FC is mixed, and halftone display becomes possible.

  Thus, the cholesteric liquid crystal is bistable, and information can be displayed using this phenomenon.

  FIG. 3 is a diagram showing the reflectance characteristics (the relationship between the voltage and the reflectance) of the cholesteric liquid crystal, and collectively shows the voltage responsiveness of the cholesteric liquid crystal described with reference to FIGS. 2A to 2C.

  As shown in FIG. 3, when the initial state is the planar state P (the portion with the high reflectivity at the left end in FIG. 3), when the pulse voltage is raised to a certain range, the driving band for the focal conic state FC is obtained, and further the pulse When the voltage is increased, the driving band for the planar state P (the high voltage portion at the right end) is reached again.

  When the initial state is the focal conic state FC (the leftmost portion having a low reflectance), the driving band for the planar state P is gradually increased as the pulse voltage is increased.

  In the planar state P, only the right circularly polarized light or the left circularly polarized light is reflected, and the remaining circularly polarized light is transmitted. Therefore, the theoretical maximum reflectance is 50%.

  Conventionally, a driving method of a liquid crystal display element that displays information by selecting a planar state and a focal conic state has been proposed in which a display element is quickly operated by phase transition driving in a fast-forward mode (for example, Patent Document 1). reference).

  Conventionally, as a method of driving a display element in a display device using a cholesteric liquid crystal, reset is performed with a predetermined number of scan lines before an image is actually written, and writing is performed after a pause is provided. A sequence has been proposed (see, for example, Patent Document 2). The prior art described in Patent Document 2 and its problems will be described in detail later.

JP 2000-171837 A International Publication No. 2005/024774 pamphlet (FIGS. 55 and 56 and Example 4)

  As described above, in recent years, electronic paper is being put into practical use using, for example, cholesteric liquid crystal. By the way, in the electronic paper, for example, a rewriting function (partial rewriting function) is required only for a specific area in the display area.

  The present applicant has filed a patent application relating to a driving method of a liquid crystal display element capable of rewriting a partial screen at high speed (Japanese Patent Application No. 2005-099711).

  4A and 4B are diagrams for explaining an example of a driving method of a display element according to related technology proposed in Japanese Patent Application No. 2005-099711. 4A and 4B, reference numeral 100 is an original image (existing image), 121 is a driver IC (scan driver) on the scanning side, 122 is a driver IC (data driver) on the data side, and 200 is after partial rewriting. An image and R0 indicate a partial rewrite area.

  In the original image 100 shown in FIG. 4A, when the partially rewritten region R0 is rewritten and the partially rewritten image 200 shown in FIG. 4B is displayed, in the related technique described above, as in the case of displaying a normal image. Instead of scanning all the scan-side areas (all scan electrodes) S10 at a normal speed and writing an image, for example, a scan-side area including the rewrite area R0 (a scan corresponding to the rewrite area R0) Electrode) Scans S12 at a normal speed to write (rewrite) an image, and scan-side area not including the rewrite area R0 (scan electrode not corresponding to the rewrite area R0: skip area) S11 and S13 at high speed It scans and maintains the original image.

  That is, in the scanning operation by the scan driver 121, first, the region S11 where partial rewriting is not performed is scanned in the high speed mode, and when reaching the region R0 where partial rewriting is performed, the image is rewritten by scanning at a normal scanning speed, and thereafter When the scan of the rewrite area R0 is completed, the area S13 where the partial rewrite is not performed is scanned in the high speed mode. This speeds up the processing operation for partial rewriting of the image.

  Here, it is most preferable to turn off the voltage output from the data driver 122 for the skip area (S11, S13) where rewriting is not performed so as not to affect the already written display image. However, since the response of the liquid crystal becomes dull by increasing the speed, it is possible to perform scanning without using this phenomenon to turn off the voltage output.

FIG. 5 is a diagram for explaining a shift in threshold characteristics due to high-speed scanning.
That is, in the high-speed mode in which the regions (S11, S13) before and after the rewrite region R0 are scanned, for example, a voltage of ± 24V or ± 32V is applied. For example, as shown in FIG. The threshold characteristic shifts greatly (shifts to the higher potential side). Specifically, the operating threshold voltage of the cholesteric liquid crystal shifts to a high voltage of 32 V or higher. For example, even when a voltage of ± 24 V or ± 32 V is applied, the liquid crystal The orientation state (display state) does not change. Therefore, in the skip regions S11 and S13, the original image can be maintained as it is by simply scanning at high speed without turning off the voltage output.

  As described above, according to the related art display element driving method, when a part of the original image is partially rewritten, it is possible to speed up the rewriting process.

  By the way, for driving the cholesteric liquid crystal, it is preferable to apply a reset voltage before writing an actual image. The applicant of the present invention, as a conventional image writing method that consumes less power and achieves stable contrast, resets a predetermined number of scan lines before actually writing an image, and further pauses. In Japanese Patent Application Laid-Open No. 2004-228561, a writing sequence for performing writing after the provision of the above has been proposed.

  6A to 6C are diagrams for explaining an example of a conventional display element driving method proposed in the above-described prior art document 2. FIG. 6A to 6C, reference numeral 100 is a previous image (existing image), 121 is a common side driver IC (scan driver), 122 is a segment side driver IC (data driver), and 200 is a new image ( The image after rewriting) is shown. FIG. 6A shows a state where the lower half is rewritten with the previous image 100 and the upper half is rewritten with a new image 200. Further, in FIG. 6C, reference symbol Eio represents a common side selection signal for selecting a scan electrode for writing data line by line, and Lp represents one line corresponding to each scan electrode (scan line). The data-side latch / scan-side shift signal for sequentially taking in the data and shifting the scan line sequentially is shown.

  As shown in FIG. 6A to FIG. 6C, conventionally, for example, when image rewriting (writing) of cholesteric liquid crystal is performed, immediately before writing a new image, in the same frame as writing, the reset period RS → the pause period PS → It has been proposed to perform image writing in the sequence of the writing section WS. In FIG. 6A, reference numeral WT indicates a write head line in the write sequence, PL indicates a pause line, and RL indicates a reset line.

  Here, although the reset line RL (reset section RS) depends on the response characteristics of the liquid crystal, about 10 to 100 lines (for example, 20 lines) and the reset section WS (reset line RL) is about 50 to 100 msec. preferable. Note that the pause section PS (pause line) may be about one line.

  Since this conventional display element driving method is reset only for a specific number of lines, the power consumption is overwhelming compared to the case where the entire screen is reset at once, and stable contrast is achieved. High display can be obtained.

  However, the conventional display element driving method described above has problems to be solved as described below.

  7A and 7B are diagrams for explaining problems in an example of a conventional display element driving method. In FIG. 7B, reference symbol R0 indicates a partial rewrite area, S21 and S23 indicate areas where high-speed skip (high-speed skip processing) is performed, and S22 indicates areas where high-speed write (high-speed write processing) is performed. Is shown.

  As shown in FIG. 7A, the conventional display element driving method described above requires a predetermined number of reset lines RL (for example, about 20 lines: reset section RS) preceding the line to be actually written. For example, when rewriting a part of the display screen (rewrite area R0) as shown in FIG. 7B, when the write line reaches near the end of the rewrite area R0, the area Rz reset by the reset line RL becomes the rewrite area. It protrudes out of R0, and the display state of the original image without partial rewriting is impaired.

  On the other hand, although it is possible to perform partial rewriting without using the reset, for example, stable writing cannot be performed unless the partial rewriting speed is reduced to 20 msec./line or less. There is a risk that an afterimage of the display pattern before rewriting occurs due to the type and some temperature fluctuations and the like, resulting in unstable partial rewriting that does not reach the original contrast. In other words, in writing without reset processing, not only afterimages and contrast decrease before rewriting occurs, but it is difficult to rewrite unless the writing speed is significantly reduced. Some shortening of rewriting time was not to be demonstrated.

  In view of the problems of the conventional display element driving method described above, the present invention can realize stable partial rewriting without impairing image quality such as afterimage and contrast reduction in a driving method using a reset pulse. An object is to provide a display element driving method and a display device.

  According to the first aspect of the present invention, a plurality of scan electrodes and a plurality of data electrodes intersecting each other in an opposing state are provided, the scan electrodes are selected in a predetermined order, and each scan electrode and each data electrode are between A display element driving method for applying a pulsed voltage to the display medium to perform an image rewriting process on a display screen, the image rewriting process including a reset pulse for initializing the display medium, and the display medium When a rewrite pulse for rewriting the image in accordance with the image data is continuously applied to perform partial rewrite on the existing display image, the scan direction is switched according to the position of the partial rewrite area on the display screen. A display element driving method is provided.

  According to the second aspect of the present invention, a plurality of scan electrodes and a plurality of data electrodes intersecting each other in an opposing state are provided, the scan electrodes are selected in a predetermined order, and each scan electrode and each of the data electrodes are arranged. A display element driving method for applying a pulsed voltage to the display medium to perform an image rewriting process on a display screen, the image rewriting process including a reset pulse for initializing the display medium, and the display medium When a rewrite pulse for continuously rewriting the image according to the image data is applied continuously and a partial rewrite is performed on the existing display image, the reset pulse selects the start line or the end line of the partial rewrite region Provided is a display element driving method characterized in that the application time is longer than the time when the start line and the end line are not selected. .

  According to the third aspect of the present invention, a plurality of scan electrodes and a plurality of data electrodes intersecting each other in an opposing state are provided, the scan electrodes are selected in a predetermined order, and the scan electrodes and the data electrodes are arranged in a predetermined order. A display device having a display element that rewrites an image on a display screen by applying a pulsed voltage to the display medium, a scan driver connected to the scan electrode, and a data driver connected to the data electrode. A reset pulse for initializing the display medium, an image rewrite processing unit that continuously applies a rewrite pulse for rewriting the display medium according to image data, and a partial rewrite in an existing display image, A scan direction switching unit that switches a scan direction according to the position of the partial rewrite area on the display screen. A display device is provided.

  According to the fourth aspect of the present invention, a plurality of scan electrodes and a plurality of data electrodes intersecting each other in an opposed state are provided, the scan electrodes are selected in a predetermined order, and the scan electrodes and the data electrodes are arranged. A display device having a display element that rewrites an image on a display screen by applying a pulsed voltage to the display medium, a scan driver connected to the scan electrode, and a data driver connected to the data electrode. A reset pulse for initializing the display medium, an image rewrite processing unit that continuously applies a rewrite pulse for rewriting the display medium according to image data, and a partial rewrite in an existing display image, The reset pulse indicates a time during which the start line or the end line of the partial rewrite area is selected. Display apparatus is provided, characterized in that it comprises a processing unit for a longer application time than the time you do not select lines, a.

  According to the fifth aspect of the present invention, a plurality of scan electrodes and a plurality of data electrodes intersecting each other in an opposing state are provided, and the scan electrodes are selected in a predetermined order, and between the scan electrodes and the data electrodes. A display device having a display element that rewrites an image on a display screen by applying a pulsed voltage to the display medium, a scan driver connected to the scan electrode, and a data driver connected to the data electrode. A reset pulse for initializing the display medium, an image rewrite processing unit that continuously applies a rewrite pulse for rewriting the display medium according to image data, and a partial rewrite in an existing display image, A display device comprising: a scan direction switching unit that switches a scan direction in accordance with a position of the partial rewrite area on the display screen. Electronic terminal, characterized in that the applied is provided.

  According to the sixth aspect of the present invention, a plurality of scan electrodes and a plurality of data electrodes intersecting each other in an opposing state are provided, the scan electrodes are selected in a predetermined order, and the scan electrodes and the data electrodes are arranged. A display device having a display element that rewrites an image on a display screen by applying a pulsed voltage to the display medium, a scan driver connected to the scan electrode, and a data driver connected to the data electrode. A reset pulse for initializing the display medium, an image rewrite processing unit that continuously applies a rewrite pulse for rewriting the display medium according to image data, and a partial rewrite in an existing display image, The reset pulse indicates a time during which the start line or the end line of the partial rewrite area is selected. Electronic terminal, wherein the processing unit for a longer application time than the time you do not select line, that of applying a display device comprising a are provided.

  According to the present invention, it is possible to provide a display element driving method and a display device capable of realizing stable partial rewriting without impairing image quality in a driving method using a reset pulse.

First, the principle of the first embodiment of the display element driving method according to the present invention will be described.
8A and 8B are diagrams for explaining the principle of the first embodiment in the display element driving method according to the present invention.

  In the display element driving method according to the present invention, the partial rewriting is performed from the start point to the end of the display screen by applying the reset pulse and the writing pulse to the same frame in the same manner as the full rewriting.

  As shown in FIG. 8A, for example, when the position of the partial rewrite region R1 is in the lower part of the display screen 300, the scan direction is the direction from the top to the bottom (S31 → S32). As shown in FIG. 8B, for example, when the position of the partial rewrite region R1 is in the upper part in the display screen 300, the scan direction is a direction from bottom to top (S34 → S33). Here, reference numerals S31 and S34 indicate areas where high-speed skip processing is performed, and S32 and S33 indicate areas where high-speed writing is performed.

  9A and 9B are diagrams for explaining image memory allocation according to a scan direction in an example of a display element driving method according to the present invention.

  As shown in FIG. 9A, for example, when the partial rewrite area R11 “Tomorrow's weather is fine” is located in the lower part of the display screen 301, the scanning direction is a direction from top to bottom. At this time, the data driver 22 receives, for example, data that is normally read from the image data in the partial rewrite area R11 stored in the memory in order from the top, that is, data that is read with the upper left of the image data as address 0. Transferred.

  On the other hand, as shown in FIG. 9B, for example, when the partial rewrite area R11 “Tomorrow's weather is fine” is located in the upper part of the display screen 301, the scan direction is from the bottom to the top. Become. At this time, for example, the data read out from the lower part of the image data in the partial rewrite area R11 stored in the memory, that is, the data read out with the lower left of the image data as the address 0 is transferred to the data driver 22, for example. Is done.

  In this way, the access procedure for the address of the image data in the partial rewrite area R11 is also switched according to the switching of the scanning direction.

  As described above, according to the present invention, it is possible to prevent the loss of display other than the rewrite region R1 due to the protrusion of the reset line described above, and it is possible to realize stable partial rewrite without an afterimage or contrast reduction. Become.

  Hereinafter, embodiments of a display element driving method and a display device according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 10 is a block diagram schematically showing a first embodiment of a display device (electronic terminal) according to the present invention. In FIG. 10, reference numeral 1 is a display element, 3 is a power supply circuit, 4 is a control circuit, 5 is an inverter, 21 is a scan driver IC (scan driver), and 22 is a data driver IC (data driver). .

  As shown in FIG. 10, the power supply circuit 3 includes a booster 31, a display element drive voltage generator (voltage generator) 32, and a regulator 33. For example, the booster 31 receives an input voltage of about +3 to +5 V from the battery, boosts the voltage to drive the display medium (display element 1), and supplies the boosted voltage to the voltage generator 32. The voltage generation unit 32 generates necessary voltages for the scan driver 21 and the data driver 22 respectively, and the regulator 33 stabilizes the voltage from the voltage generation unit 32 and supplies it to the scan driver 21 and the data driver 22. .

  The control circuit 4 includes a partial rewrite input unit 41, an image data generation unit 42, a position information generation unit 43, and a data conversion circuit 44. The control circuit 4 calculates image data and control signals supplied from the outside, and when an image pattern to be partially rewritten and a position in the display screen to input it are input, the data conversion circuit 44 responds to the information. The scanning direction of the scan driver 21 is determined, and image data input to the driver 21 is rearranged as necessary.

  That is, the partial rewriting input unit 41 recognizes partial rewriting from image data and control signals supplied from the outside, generates image data of an area where partial rewriting is performed by the image data generation unit 42, and a position information generation unit 43. The position information of the area to be partially rewritten (position information in the display area of the rewrite area) is generated. The image data and position information of these rewrite areas are input to the data conversion circuit 44, and the scan direction signal CS1, the data capture clock CS2, the pulse polarity control signal CS3, and the frame start signal CS4 that determine the scan direction of the scan driver 21 described above. , A data latch / scan shift signal CS5 and a driver output cutoff signal CS6 are output.

  Here, the data capture clock CS2 is supplied to the driver set in the data mode, and is a signal for sequentially capturing data for one line (in the case of partial rewriting, data in a region to be rewritten). The polarity control signal CS3 is a signal for inversion control of the polarity of the pulse voltage applied to the display element 1, the frame start signal CS4 is a signal indicating the start of an image of one frame, and the data latch / scan shift signal CS5. Is a signal for performing synchronous control of a line in which data is stored by the data driver and a line selected by the scan driver, and the driver output cutoff signal CS6 cuts off the driver output of the data driver or scan driver It is a signal for.

  In other words, when rewriting a partial area in an existing display image, if the rewritten area is in the lower part of the display screen, the scan direction is the direction from the top to the bottom of the display screen. If the rewriting area is in the upper part of the display screen, the scanning direction is the direction from the bottom to the top of the display screen. Note that the display element driving method according to the present invention will be described in detail later.

  11 is a cross-sectional view schematically showing an example of a display element (liquid crystal display element) in the display device shown in FIG. In FIG. 11, reference numerals 11 and 12 are film substrates, 13 and 14 are transparent electrodes (for example, ITO), 15 is a liquid crystal composition (cholesteric liquid crystal), 16 and 17 are sealing materials, 18 is a light absorbing layer, and Reference numeral 19 denotes a drive circuit.

  The display element 1 includes a liquid crystal composition 15, and transparent electrodes 13 and 14 that intersect perpendicularly are formed on the inner surfaces of the transparent film substrates 11 and 12 (surfaces in which the liquid crystal composition 15 is sealed), respectively. ing. That is, a plurality of scan electrodes 13 and a plurality of data electrodes 14 are formed in a matrix on opposing film substrates 11 and 12. In FIG. 11, the scan electrodes 13 and the data electrodes 14 are drawn so as to be parallel at first glance. However, actually, for example, a plurality of data electrodes 14 intersect one scan electrode 13. Needless to say. Furthermore, the thickness of each film substrate 11 and 12 is, for example, about 0.2 mm, and the thickness of the liquid crystal composition 15 is, for example, about 3 μm to 6 μm. Their ratio is ignored.

  Here, the electrodes 13 and 14 are preferably coated with an insulating thin film or an alignment stabilizing film. Further, a visible light absorption layer 18 is provided on the outer surface (back surface) of the substrate (12) opposite to the side on which light is incident, if necessary.

  In this example, the liquid crystal composition 15 is a cholesteric liquid crystal exhibiting a cholesteric phase at room temperature, and these materials and combinations thereof will be specifically described by the following experimental examples.

  The sealing materials 16 and 17 are for sealing the liquid crystal composition 15 between the film substrates 11 and 12. The drive circuit 19 is for applying a predetermined pulse voltage to the electrodes 13 and 14.

  Although the film substrates 11 and 12 both have translucency, at least one of the pair of substrates that can be used as the display element 1 of this embodiment needs to have translucency. It is. In addition, although a glass substrate can be illustrated as a board | substrate which has translucency, flexible resin film substrates, such as PET and PC, can be used besides a glass substrate. In addition, as the electrodes 13 and 14, for example, ITO (Indium Tin Oxide) is representative, but in addition, for example, a transparent conductive film such as IZO (Indium Zinc Oxide). Alternatively, a metal electrode such as aluminum or silicon, or a photoconductive film such as amorphous silicon or BSO (Bismuth Silicon Oxide) can be used.

  In the liquid crystal display element shown in FIG. 11, as described above, a plurality of strip-like transparent electrodes 13 and 14 parallel to each other are formed on the inner surfaces of the transparent film substrates 11 and 12, and these electrodes 13 and 14 are formed on the substrate. They face each other so as to intersect each other when viewed from a direction perpendicular to the direction.

  In the display element according to the present invention, an insulating thin film having a function of preventing a short circuit between the electrodes or improving the reliability of the liquid crystal display element as a gas barrier layer may be formed. Examples of the orientation stabilizing film include organic films such as polyimide resin, polyamideimide resin, polyetherimide resin, polyvinyl butyral resin, and acrylic resin, or inorganic materials such as silicon oxide and aluminum oxide. The alignment stabilizing film coated on the electrodes 13 and 14 can also be used as an insulating thin film.

  The liquid crystal display element according to the present invention may be provided with a spacer between the pair of substrates for uniformly holding the inter-substrate gap. Examples of the spacer include F spheres made of resin or inorganic oxide. Further, a fixed spacer whose surface is coated with a thermoplastic resin can also be suitably used.

  The substance constituting the liquid crystal composition (liquid crystal layer) 15 is, for example, cholesteric liquid crystal obtained by adding 10 to 40 wt% of a chiral agent to the nematic liquid crystal composition. Here, the addition amount of the chiral agent is a value when the total amount of the nematic liquid crystal component and the chiral agent is 100 wt%.

  Various types of conventionally known nematic liquid crystals can be used as the nematic liquid crystal, but a dielectric anisotropy of 20 or more is preferable for the convenience of driving voltage. That is, when the dielectric anisotropy is 20 or more, the driving voltage is relatively low. The dielectric anisotropy (Δε) of the cholesteric liquid crystal composition is preferably 20-50. Within this range, general-purpose drivers can be used.

  The refractive index anisotropy (Δn) is preferably 0.18 to 0.24. If it is smaller than this range, the reflectivity in the planar state is lowered, and if it is larger than this range, the scattering reflection in the focal conic state is increased and the viscosity is increased and the response speed is lowered. The thickness of the liquid crystal is preferably about 3 μm to 6 μm. If the thickness is smaller than this, the planar reflectivity is lowered, and if it is larger, the driving voltage becomes too high.

  FIG. 12A is a diagram for explaining an embodiment of a display element driving method according to the present invention, and FIGS. 13A to 13C are diagrams for explaining an embodiment of a display element driving method according to the present invention. It is a flowchart of.

  In FIG. 12A, the common side (scan driver 21) is configured by two scan drivers 211 and 212. FIG. Note that the flowcharts shown in FIGS. 13A to 13C explain the operation when only two scan drivers shown in FIG. 12A are provided.

  First, in step ST1, partial rewrite conditions, that is, image data Example.dat (u, v) are set. In step ST2, the image data Example.dat (u, v) is stored in the memory. In step ST3, the rewrite position is stored in the memory. In step ST4, it is determined whether or not the position of the partial rewrite image (partial rewrite region R2) straddles the two scan drivers 211 and 212.

  If it is determined in step ST4 that the position of the partial rewrite region R2 crosses the two scan drivers 211 and 212, the process proceeds to step ST5, the partial scan is started by the first scan driver 211, and the process proceeds to step ST6. Here, when the position of the partial rewrite region R2 straddles the two scan drivers 211 and 212, it is a case where the rewrite region R2 is positioned below the display screen corresponding to the first scan driver 211. The scan direction 211 is a direction from the top to the bottom of the display screen. The scanning direction from the top to the bottom is determined in advance as the basic scanning direction.

  In step ST6, the first scan driver 211 performs high-speed skip processing of the region S41, and further proceeds to step ST14, where the first scan driver 211 writes the image to the region S42 corresponding to a part of the rewrite region R2. To start.

  Further, in step ST15, image data Example.dat (u, v) is input to the data driver 22. In this case, the memory access order is forward, and the coordinate data (0, 0), (1, 0), line of each line from which the image data Example.dat (u, v) stored in the memory is read. (2, 0), ..., (u-1, 0); (0, 1), (1, 1), (2, 1), ..., (u-1, 1); v−1), (1, v−1), (2, v−1),..., (u−1, v−1) are sequentially written in the data driver 22 corresponding to each scan line in the region S42. .

  Then, the process proceeds to step ST16, the voltage pulse output (32V or 24V) is applied to the corresponding data electrode, and the process proceeds to step ST17, where the writing by the first scan driver 211 is completed.

  Next, proceeding to step ST26, the scan direction of the second scan driver 212 is switched from the bottom to the top of the display screen opposite to the basic scan direction. Here, when the position of the partial rewrite region R2 crosses the two scan drivers 211 and 212, the rewrite region R2 is located above the display screen corresponding to the second scan driver 212, so the scan driver The scan direction 212 is a direction from the bottom to the top of the display screen.

  In step ST27, the second scan driver 212 performs high-speed skip processing of the area S44, and further proceeds to step ST28, in which the second scan driver 212 corresponds to a part of the rewrite area R2. Image writing to S43 is started.

  Further, in step ST29, image data Example.dat (u, v) is input to the data driver 22. In this case, the memory access order is in the upside down direction, and the image data stored in the memory Example.dat (u, v) is read out from the coordinate data (0, v−1), (1, v) of each line. -1), (2, v-1), ..., (u-1, v-1); (0, v-2), (1, v-2), (2, v-2), ..., (U-1, v-2); ...; (0, 0), (1, 0), (2, 0), ..., (u-1, 0) sequentially correspond to each scan line in the region S43. And write to the data driver 22.

  Then, the process proceeds to step ST30, the voltage pulse output (32V or 24V) is applied to the corresponding data electrode, the process proceeds to step ST31, the writing by the second scan driver 212 is terminated, and the process proceeds to step ST32. Then, the partial rewriting (writing of the rewriting area R2) is finished.

  On the other hand, when it is determined in step ST4 that the position of the partial rewrite area (R2) does not straddle the two scan drivers 211 and 212, that is, the partial rewrite area is included in the area of one scan driver. Proceeding to ST7, it is determined whether the partial rewrite area is included in the area of the first scan driver 211 or the area of the second scan driver 212, and the process proceeds to step ST8. In step ST8, whether or not the distance from the partial rewrite area to the data driver 22 is long, that is, the upper length from the partial rewrite area to the upper end of the display screen ≧ the lower length from the partial rewrite area to the lower end of the display screen Determine the thickness.

  If it is determined in step ST8 that the upper length ≧ the lower length, that is, in the first or second scan driver (scan driver including the rewrite area) that scans the area including the partial rewrite area. If it is determined that the partial rewrite area is below the display screen corresponding to the scan driver including the rewrite area, the process proceeds to step ST9 to start partial rewrite with the scan driver including the rewrite area, and to step ST10. move on.

  In step ST10, high-speed skip processing is performed by the scan driver including the rewrite area. Further, the process proceeds to step ST18, and image writing is started by the scan driver including the rewrite area. Further, the process proceeds to step ST19, where image data Example. dat (u, v) is input to the data driver 22. In this case, the memory access order is forward as in step ST15 described above.

  Then, the process proceeds to step ST20, the voltage pulse output (32V or 24V) is applied to the corresponding data electrode, the process proceeds to step ST21, the writing by the scan driver including the rewrite area is terminated, and the process proceeds to step ST32. Finish rewriting.

  If it is determined in step ST8 that the upper length is not greater than the lower length, that is, it is determined that the partial rewrite area is above the display screen corresponding to the scan driver including the rewrite area. Then, the process proceeds to step ST11, the scan direction of the scan driver including the rewrite area is switched from the bottom to the top of the display screen opposite to the basic scan direction, and the process proceeds to step ST12.

  In step ST12, partial rewriting is started with a scan driver including a rewriting area, the process proceeds to step ST13, and high-speed skip processing is performed by the scan driver including the rewriting area, and the process proceeds to step ST22, and the scan driver including the rewriting area is performed. To start image writing.

  In step ST23, the image data Example.dat (u, v) is input to the data driver 22. In this case, as in step ST29 described above, the memory access order is in the upside down direction.

  Then, the process proceeds to step ST24, the voltage pulse output (32V or 24V) is applied to the corresponding data electrode, the process proceeds to step ST25, the writing by the scan driver including the rewrite area is terminated, and the process proceeds to step ST32. Finish rewriting.

12B is a diagram for explaining a modification of the display element driving method shown in FIG. 12A.
In the above description, the common side as shown in FIG. 12A is constituted by two scan drivers 211 and 212, and the segment side is constituted by one data driver 22 provided at one end (upper end) of the display screen. Although the element has been described, for example, the common side as shown in FIG. 12B is configured by two scan drivers 211 and 212, and the segment side is provided with two data drivers provided at both ends (upper end and lower end) of the display screen. The present invention can be similarly applied to the display elements constituted by 221 and 222.

  Note that in the display element having the two scan drivers 211 and 212 as shown in FIG. 12B, the first write process by the first scan driver 211 and the first data driver 221 and the second scan driver 212 are performed. It is also possible to perform the second write process by the second data driver 222 in parallel (simultaneously). That is, in the display element (display device) shown in FIG. 12B, the first scan driver 211 performs high-speed skip processing in the scan direction (downward) from the top to the bottom of the region S45 and the bottom of the region S48 by the second scan driver 212. The high-speed skip process in the scan direction (upward) from the top to the top is simultaneously performed, and the high-speed write process in the downward direction of the area S46 by the first scan driver 211 and the high-speed write in the upward direction of the area S47 by the second scan driver 212 By simultaneously performing the processing, it is possible to further reduce the time required for partial rewriting.

  14A and 14B are diagrams for explaining another embodiment of the display element driving method according to the present invention.

  14A shows that the common side (scan driver 21) is composed of four scan drivers 211 to 214, and FIG. 14B is just that the common side is composed of four scan drivers 211 to 214 as in FIG. 14A. In addition, the segment side (data driver 22) is also composed of two data drivers 221 and 222 provided at the upper and lower ends of the display screen.

  Note that when the positional relationship between the first to fourth scan drivers 211 to 214 and the partially rewritten image (partially rewritten region R3) is as shown in FIG. 14A, for example, the first scan driver 211 sequentially changes the region S51. The downward high-speed skip processing, the downward high-speed skip processing of the region S52 by the second scan driver 212, the downward high-speed writing processing of the region S53 by the second scan driver 212, and the region S54 by the third scan driver 213 The downward high-speed writing process is performed, and then the upward high-speed skip process of the area S56 by the fourth scan driver 214 and the upward high-speed writing process of the area S55 by the fourth scan driver 214 are performed.

  Further, when the positional relationship between the first to fourth scan drivers 211 to 214 and the partial rewrite region R3 is as shown in FIG. 14B, for example, the first scan driver 211 sequentially performs the downward high-speed skip processing in the region S61. And the fourth scan driver 214 simultaneously perform the upward high-speed skip process in the area S66, and the second scan driver 212 performs the downward high-speed skip process in the area S62 and the fourth scan driver 214 in the upward direction in the area S65. The high-speed writing process is simultaneously performed, and the downward high-speed writing process of the area S63 by the second scan driver 212 and the upward high-speed writing process of the area S64 by the third scan driver 213 are simultaneously performed.

  Thus, the number of common side scan drivers may be plural, and the number of segment side data drivers may be one at one end of the display screen or two at both ends of the display screen.

  For example, for some lines from the write start line for partial rewriting, a write pulse is directly applied without being given a reset pulse, or a predetermined display characteristic is not achieved because the number of lines to which a reset pulse is given is insufficient. It may not be obtained. Therefore, for example, it is preferable to apply the reset pulse in advance only to the line to which the reset pulse is not applied or to increase the pulse application time by reducing the scanning speed.

  Incidentally, as described above with reference to FIG. 7B and the like, in the conventional display element driving method, when a part of the display screen (rewrite region R0) is rewritten, the write line is close to the end of the rewrite region R0. When it reaches, the area Rz reset by the reset line RL protrudes outside the rewrite area R0, and the display state of the original image that is not partially rewritten is impaired. Further, when partial rewriting is performed without resetting, for example, the writing speed has to be greatly reduced, and the rewriting time, which is the original merit of partial rewriting, cannot be reduced.

  15A and 15B are views for explaining still another embodiment of the display element driving method according to the present invention.

  The display element driving method of this embodiment is characterized in that the reset period and the writing period are performed in different frames (frame division) at the time of partial rewriting.

  That is, as shown in FIG. 15A, first, in the first frame, for example, the high-speed skip processing of the region S71 is performed in the scan direction from top to bottom, and then the scan line corresponding to the partial rewrite region R4 ( The reset process of area S72) is performed, and the high-speed skip process of area S73 is further performed. Thereby, for example, in a display element using cholesteric liquid crystal, the region S72 corresponding to the partial rewrite region R4 is in a planar state.

  Then, in the next second frame, for example, high-speed skip processing of the region S71 is performed in the scan direction from top to bottom, and then high-speed writing processing of the rewritten image is performed in the region S72 corresponding to the partial rewrite region R4. Further, the high-speed skip process for the area S73 is performed.

  Note that while the partial rewrite region is scanned, the difference voltage between the scan electrode and the data electrode is set to be equal to or lower than the response value voltage of the display medium (for example, cholesteric liquid crystal).

  Thereby, it is possible to avoid the reset region (Rz) from protruding from the rewrite region. In addition, since the number of selected lines is limited in the reset period, an increase in power consumption can be suppressed.

  In this case as well, for example, the number of lines from the beginning of partial rewriting and the number of lines from before the end of writing may not be able to obtain predetermined display characteristics because the number of reset lines is insufficient at a constant scanning speed. . For this reason, when the reset pulse selects the start line and the end line of partial rewriting, it is effective to reduce the scan speed and increase the pulse application time to compensate for the reset effect. The reset time is the scan speed × the number of reset lines.

  In FIG. 16, reference numeral 101 is a blue (B) layer that reflects blue light, 102 is a green (G) layer that reflects green light, and 103 is a red (R) layer that reflects red light. Show. Note that a black (K) layer that absorbs light may be provided under the R layer 103.

  As shown in FIG. 16, the display device of the second embodiment has scan drivers 2101, 2102 and 2103, and data drivers 2201, 2202 and 2203 for the B layer 101, the G layer 102 and the R layer 103, respectively. 2203 is provided. In each of the layers 101, 102, and 103, scan electrodes and data that are connected to the scan drivers 2101, 2102, and 2103, and the data drivers 2201, 2202, and 2203 and intersect each other with the cholesteric liquid crystal (display medium) interposed therebetween. With the electrodes, the display element 1 can perform display close to full color.

FIG. 17 is a diagram schematically showing a main part of a third embodiment of the display device according to the present invention.
As shown in FIG. 17, the display device according to the third embodiment has a common scan driver 21 and individual data drivers 2201, 2202, and 2203 for the B layer 101, the G layer 102, and the R layer 103. Is provided.

  In this way, by sharing the scan driver between the B layer 101, the G layer 102, and the R layer 103, the number of drivers and the like can be reduced and the cost can be reduced.

  Hereinafter, the driving voltage of the QVGA color display device manufactured by applying the display device of the second embodiment shown in FIG. 16 will be described with reference to FIGS. 18A to 18D. Note that general-purpose STN drivers were used as the scan drivers 2101 to 2103 and the data drivers 2201 to 2203. Further, if necessary, a voltage follower of an operational amplifier may be applied to stabilize the voltage input to each driver.

  18A is a diagram illustrating an example of an input voltage to the driver in the scan mode and the data mode, FIG. 18B is a diagram illustrating an example of correspondence when driving the cholesteric liquid crystal, and FIG. 18C is an output voltage of the driver in the scan mode and the data mode. FIG. 18D is a diagram illustrating an example of a composite waveform applied to the liquid crystal.

  First, as shown in FIGS. 18A and 18B, in the data mode (segment mode: data driver), an arbitrary line can be selected. A high level “H” data signal can be selected with respect to a high level “H” data signal. As the AC signal, the voltage V0 (32V) and the low level “L” AC signal are the voltage V5 (0 V), and the low level “L” data signal is the high level “H” AC signal. The voltage V34 (4V) is used as the AC signal of the voltage V21 (28V) and the low level “L”.

  In scan mode (common mode: scan driver), any line cannot be selected. All lines are scanned, and a high level “H” data signal is a voltage as a high level “H” AC signal. The voltage V0 (32V) as an AC signal of V5 (0V) and low level “L”, and the voltage V21 (28V) as an AC signal of high level “H” with respect to a data signal of low level “L”. The voltage V34 (4V) is used as the low level “L” AC signal. Here, the relationship of V0 ≧ V21 ≧ V34 ≧ V5 is established.

  In each of the RGB elements (R layer 103, G layer 102, and B layer 101), a pulse voltage of ± 32V is stably applied to on pixels and ± 24V is applied to off pixels, and non-selected pixels are applied to non-selected pixels. A pulse voltage of ± 4 V is applied. That is, as shown in FIG. 18B, the scan driver (common driver: COM) and the data driver (segment driver: SEG) include, for example, 32V, 28V, 24V, 8V, generated by the power supply circuit 3 in FIG. Voltages of 6 levels of 4V and 0V are input.

  Therefore, 32V, 28V, 4V, and 0V are input to the scan mode driver, and 32V, 24V, 8V, and 0V are input to the data mode driver, and the scan mode and data mode of the driver are switched. Each voltage input to the drivers is also switched.

  As shown in FIG. 18C, the output voltage when the scan driver is turned on and off is 0V in the first half of the AC drive for the ON-COM and 32V in the second half, and 28V in the first half of the AC drive of the OFF-COM and the second half in the second half. The output voltage when the data driver is on and off is 32V in the first half of the AC drive for the ON-SEG and 0V in the second half, and 24V in the first half of the AC drive for the OFF-SEG and 24V in the second half. It is 8V.

  As shown in FIG. 18D, the liquid crystal (pixel) between each scan electrode and each data electrode has a pulse waveform of 32V for the first half AV11 of the AC drive and -32V for the second half AV21 for the liquid crystal selected on. The first half AV12 of AC driving is applied with a pulse waveform of 24V and the latter half AV22 is applied with a pulse waveform of −24V, and the first half AV13 of AC driving is 4V and the latter half of AV23 is applied to a non-selected ON liquid crystal. A pulse waveform of −4V is applied, and to the non-selection-off liquid crystal, a pulse waveform of −4V is applied to the first half AV14 of AC drive and 4V is applied to the second half AV24.

  An area where partial rewriting is performed is scanned at a speed of about 10 msec./line, for example, and a non-target area where partial rewriting is not performed is instantaneously scanned at a scanning speed of about μsec. / Line, for example. It will be. Note that when scanning non-target areas, it is preferable to turn off the voltage output from the driver, but if the voltage is below the voltage that the liquid crystal (pixel) responds to during high-speed scanning, the previous image will be maintained, which is problematic There is no.

  As described above, the present invention can be applied to, for example, a display element capable of full-color display in which the B layer 101, the G layer 102, and the R layer 103 are stacked, and an image to be partially rewritten (rewrite region) Full-color rewriting can be performed by rewriting all the layers. For example, only the G layer 102 can be rewritten.

  The present invention is not limited to cholesteric liquid crystals, and is widely applied to, for example, electronic devices using other liquid crystals that require reset processing before rewriting processing and electronic terminals having a display device using the same. Can do.

It is FIG. (1) for demonstrating the orientation state of a cholesteric liquid crystal. FIG. 3 is a diagram (part 2) for explaining the alignment state of the cholesteric liquid crystal. FIG. 3 is a diagram (part 1) illustrating voltage characteristics for driving a cholesteric liquid crystal. FIG. 6 is a diagram (part 2) illustrating voltage characteristics for driving a cholesteric liquid crystal. FIG. 6 is a diagram (part 3) illustrating voltage characteristics for driving a cholesteric liquid crystal. It is a figure which shows the reflectance characteristic of a cholesteric liquid crystal. It is FIG. (1) for demonstrating an example of the drive method of the display element of related technology. It is FIG. (2) for demonstrating an example of the drive method of the display element of related technology. It is a figure for demonstrating the shift of the threshold characteristic by a high-speed scan. It is FIG. (1) for demonstrating an example of the driving method of the conventional display element. It is FIG. (2) for demonstrating an example of the driving method of the conventional display element. It is FIG. (3) for demonstrating an example of the driving method of the conventional display element. It is FIG. (1) for demonstrating the subject in an example of the driving method of the conventional display element. It is FIG. (2) for demonstrating the subject in an example of the driving method of the conventional display element. It is FIG. (1) for demonstrating the principle of the 1st form in the drive method of the display element which concerns on this invention. FIG. 6 is a diagram (No. 2) for explaining the principle of the first embodiment in the display element driving method according to the present invention; FIG. 6 is a diagram (No. 1) for explaining the allocation of the image memory according to the scan direction in an example of the display element driving method according to the invention. FIG. 10 is a diagram (No. 2) for explaining the allocation of the image memory according to the scan direction in the example of the display element driving method according to the invention. 1 is a block diagram schematically showing a first embodiment of a display device according to the present invention. It is sectional drawing which shows roughly an example of the display element in the display apparatus shown in FIG. It is a figure for demonstrating one Example of the drive method of the display element which concerns on this invention. It is a figure for demonstrating the modification of the drive method of the display element shown to FIG. 12A. It is a flowchart (the 1) for demonstrating one Example of the drive method of the display element which concerns on this invention. It is a flowchart (the 2) for demonstrating one Example of the drive method of the display element which concerns on this invention. It is a flowchart (the 3) for demonstrating one Example of the drive method of the display element which concerns on this invention. It is FIG. (1) for demonstrating the other Example of the drive method of the display element which concerns on this invention. It is FIG. (2) for demonstrating the other Example of the drive method of the display element which concerns on this invention. It is FIG. (1) for demonstrating the further another Example of the drive method of the display element which concerns on this invention. It is FIG. (2) for demonstrating other Example of the drive method of the display element which concerns on this invention. It is a figure which shows typically the principal part of 2nd Example of the display apparatus which concerns on this invention. It is a figure which shows typically the principal part of 3rd Example of the display apparatus which concerns on this invention. It is a figure which shows an example of the input voltage to the driver in a scan mode and a data mode. It is a figure which shows an example of a response | compatibility in the case of driving a cholesteric liquid crystal. It is a figure which shows an example of the output voltage of the driver in a scan mode and a data mode. It is a figure which shows an example of the synthetic | combination waveform applied to a liquid crystal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Display element 3 Power supply circuit 4 Control circuit 11, 12 Film board | substrate 13, 14 Transparent electrode (ITO)
15 Liquid crystal composition (cholesteric liquid crystal)
16, 17 Seal material 18 Light absorption layer 19 Drive circuit 21; 211, 212, 213, 214; 2101, 1022, 2103 Scan driver IC (scan driver)
22; 221, 222, 223, 224; 2201, 2202, 2203 Data driver IC (data driver)
31 Booster 32 Voltage generator 33 Regulator 41 Partial rewrite input unit 42 Image data generator 43 Position information generator 44 Data conversion circuit (image rewrite processor / scan direction switching unit)
100 Original image (existing image)
101 Blue (B) layer 102 Green (G) layer 103 Red (R) layer 121 Driver IC (scan driver) on the scanning side
122 Data side driver IC (data driver)
200 Image after partial rewriting FC Focal conic state H Homeotropic state P Planar state R0, R1, R2, R3, R4 Partial rewriting area

Claims (16)

A plurality of scan electrodes and a plurality of data electrodes intersecting each other in an opposing state, and selecting the scan electrodes in a predetermined order and applying a pulsed voltage to a display medium between the scan electrodes and the data electrodes A display element driving method for performing image rewriting processing on the display screen,
The image rewriting process continuously applies a reset pulse for initializing the display medium and a rewrite pulse for rewriting the display medium according to image data,
A method for driving a display element, characterized in that, when partial rewriting is performed on an existing display image, the scanning direction is switched according to the position of the partial rewriting area on the display screen. The display element driving method according to claim 1,
The display element driving method, wherein the reset pulse and the rewrite pulse are applied to the partial rewrite region in the same frame. The display element driving method according to claim 1 or 2,
When the partial rewrite area is below the display screen corresponding to the scan driver, the scan direction of the scan driver is a direction from the top to the bottom of the display screen, and the partial rewrite area When the rewrite area is above the display screen corresponding to the scan driver, the scan direction of the scan driver is a direction from the bottom to the top of the display screen. . A plurality of scan electrodes and a plurality of data electrodes intersecting each other in an opposing state, and selecting the scan electrodes in a predetermined order and applying a pulsed voltage to a display medium between the scan electrodes and the data electrodes A display element driving method for performing image rewriting processing on the display screen,
The image rewriting process continuously applies a reset pulse for initializing the display medium and a rewrite pulse for rewriting the display medium according to image data,
When performing partial rewriting in an existing display image, the reset pulse does not select the start line and the end line while selecting the start line or end line of the partial rewrite area. A display element driving method, wherein an application time is longer than the time. The display element driving method according to claim 4,
The number of selected lines of the reset pulse is equal to or less than the number of partial rewrite lines. The display element driving method according to claim 5,
The display element driving method, wherein the reset pulse and the rewrite pulse are applied to the partial rewrite region in different frames. In the driving method of the display element according to claim 1 or 4,
The method of driving a display element, wherein the reset pulse causes the partial rewrite region to be in a planar state. A plurality of scan electrodes and a plurality of data electrodes intersecting each other in an opposing state, and selecting the scan electrodes in a predetermined order and applying a pulsed voltage to a display medium between the scan electrodes and the data electrodes A display device that rewrites an image on a display screen, a scan driver connected to the scan electrode, and a data driver connected to the data electrode,
An image rewrite processing unit for continuously applying a reset pulse for initializing the display medium, and a rewrite pulse for rewriting the display medium according to image data;
A display device comprising: a scan direction switching unit that switches a scan direction in accordance with a position of the partial rewrite area on the display screen when performing partial rewrite on an existing display image. The display device according to claim 8, wherein
The display device includes one scan driver,
When the partial rewrite area is below the display screen corresponding to the scan driver, the scan direction switching unit sets the scan direction of the scan driver from the top to the bottom of the display screen. In addition, when the partial rewrite area is above the display screen corresponding to the scan driver, the scan direction of the scan driver is set to be a direction from the bottom to the top of the display screen. Display device. The display device according to claim 8, wherein
The display device includes a plurality of scan drivers,
When the partial rewrite area is below the display screen corresponding to each scan driver, the scan direction switching unit moves the scan direction of each scan driver from the top to the bottom of the display screen. And when the partial rewrite area is above the display screen corresponding to each scan driver, the scan direction of each scan driver is a direction from the bottom to the top of the display screen. A display device characterized by: The display device according to claim 10.
The display device includes first and second data drivers provided at both ends of the display screen,
A first image rewriting process by an arbitrary first scan driver in the first data driver and the plurality of scan drivers, and another second scan in the second data driver and the plurality of scan drivers. A display device that performs a second image rewriting process by a driver at the same time. A plurality of scan electrodes and a plurality of data electrodes intersecting each other in an opposing state, and selecting the scan electrodes in a predetermined order and applying a pulsed voltage to a display medium between the scan electrodes and the data electrodes A display device that rewrites an image on a display screen, a scan driver connected to the scan electrode, and a data driver connected to the data electrode,
An image rewrite processing unit for continuously applying a reset pulse for initializing the display medium, and a rewrite pulse for rewriting the display medium according to image data;
When performing partial rewriting in an existing display image, the reset pulse does not select the start line and the end line while selecting the start line or end line of the partial rewrite area. And a processing unit for applying an application time longer than the time. The display device according to claim 8 or 12,
The display device is characterized in that the display medium has a memory property. The display device according to claim 13,
The display device, wherein the display medium is a liquid crystal forming a cholesteric phase. The display device according to claim 8 or 12,
The display device has a laminated structure of a plurality of display element units having different reflected light.   An electronic terminal, wherein the display device according to claim 8 is applied.

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