JP2007264389A - Driver for image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driver for an image display device which generates multi-step voltage values by a less number of level shifters and combines, and applies the multi-step voltage values to data electrodes or scan electrodes of the image display device. <P>SOLUTION: The driver for the image display device which changes alignment states of liquid crystal by applying one of voltages set in multiple steps to the plurality of data electrodes or scan electrodes while switching them in every predetermined voltage application period is provided with a section selecting circuit 402 which inputs period information regarding the voltage application period, a supply voltage selecting unit 401 which selects a value of the voltage to be applied to the data electrodes or scan electrodes 407 in the period that the period information designates among the values of the voltages set in eight stages based upon the period information input by the section selecting circuit 402, and level shifters 405a to 405d and an output transistor unit 406 which generate a pulse voltage corresponding to the selected voltage value and apply the voltage to the data electrodes or scan electrodes 407. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image display device driver, and more particularly to an image display device driver that applies a voltage having a pattern configured by combining voltages set in multiple stages to an electrode of the image display device.

Currently, liquid crystal displays using cholesteric liquid crystals are in practical use. A liquid crystal display using a cholesteric liquid crystal is also called a memory liquid crystal display because it can maintain an image once drawn without supplying a voltage. A low power consumption memory liquid crystal display has a structure suitable for a portable display device.
As a technique for speeding up image rewriting in cholesteric liquid crystal, there is DDS (Dynamic Drive scheme) driving. The DDS drive is to switch the orientation of the cholesteric liquid crystal to the planar orientation or the focal conic orientation by applying a voltage having a waveform generated by combining a plurality of levels of voltages to the scan electrode and the data electrode of the display.

As a conventional technique of DDS, for example, Patent Document 1 can be cited.
US Pat. No. 5,748,277

  However, the DDS drive described in Patent Document 1 needs to supply eight levels of voltage values to the display. In the prior art, in order to be able to select the eight levels of voltage values required for DDS driving, the voltage selection signal generated from the input data value is converted from low voltage to high voltage by a level shifter. , One voltage value can be selected from eight voltage levels. Therefore, in order to be able to select eight voltage values, eight level shifters are required for each output pin of the driver.

  Therefore, for example, in order to realize a DDS driver having 240 output pins, 8 × 240 = 1920 level shifters are required. Since the level shifter requires a large transistor size due to the driving capability, the occupied area becomes large. Therefore, reducing the number of level shifters is effective in reducing the size of the DDS driver chip, and can lead to a reduction in chip cost.

  An object of the present invention is to provide an image display device driver that selects eight levels of voltage with a smaller number of level shifters and applies the eight levels of voltage values to scan electrodes and data electrodes of the image display device. And

  In order to solve the above-described problems, the image display device driver according to the present invention applies one of a plurality of voltages set to each of a plurality of data electrodes and scanning electrodes while switching every predetermined voltage application period. Thus, a driver of the image display device for changing the alignment state of the liquid crystal, the period information input means for inputting information relating to the voltage application period, and the period information input by the period information input means Voltage selection means for selecting a voltage value applied to the data electrode or the scan electrode during a period indicated by period information among a plurality of voltage values set in stages, and a voltage value selected by the voltage selection means And a voltage applying means for generating a pulse voltage and applying the pulse voltage to the data electrode or the scanning electrode.

  According to such an invention, one of the voltages set in multiple stages is applied to each of a plurality of data electrodes or scanning electrodes while switching every predetermined voltage application period, and the alignment state of the liquid crystal to which the voltage is applied A driver of an image display device that changes voltage, inputs information related to a voltage application period, and applies it to the data electrode or scan electrode during a period indicated by period information among a plurality of voltage values set in multiple stages The voltage value to be selected can be selected. Then, a pulse voltage having a selected voltage value can be generated and applied to the data electrode or the scan electrode.

  Therefore, the present invention can output all voltage values necessary for DDS driving while only having a configuration for generating a voltage that is used simultaneously during a voltage application period. This eliminates the need for a configuration that can select all of the multi-stage voltage values, thereby reducing the number of level shifters, reducing the circuit scale, and reducing the driver size. As a result, the driver cost can be reduced.

In the image display device driver according to the present invention, the voltage application unit selects a number of level shifters corresponding to the number of voltage values selected by the voltage selection unit and a predetermined voltage converted by the level shifter. Voltage output means for outputting a pulse voltage having a voltage value selected on the basis of a signal for the purpose.
According to such an invention, the number of level shifters having a large influence on the size of the driver can be made to be a selected partial number among the number of voltage values used in the DDS drive. Therefore, the number of level shifters can be reduced, the circuit scale can be reduced, and the driver size can be reduced.

Embodiments of an image display device driver according to the present invention will be described below with reference to the drawings.
First, DDS driving will be described prior to description of the image display device driver of the present embodiment. FIG. 1 is a diagram for explaining an alignment state of cholesteric liquid crystal in a display. The display is configured by enclosing a cholesteric liquid crystal 4 between a glass substrate 1 on which a transparent electrode 3 is formed, and providing a light absorption layer 2 in the lowermost layer.

  When a voltage is applied to such a display, the liquid crystal can take three alignment states shown in FIGS. In the planar alignment shown in FIG. 1A, light is reflected by the direction of the axis of the liquid crystal without reaching the light absorption layer 2. In such a state, the display displays white of the image by selective reflection. Further, in the focal conic orientation shown in (b) and the homeotropic orientation shown in (c), the light incident on the display reaches the light absorption layer 2 and the black image is displayed. In FIGS. 1A and 1B, the state is maintained even when no voltage is applied, so that the white state or the black state can be stably maintained as the memory display body.

  FIG. 2 shows the timing of voltage application in DDS (Dynamic Drive Scheme) driving that can change the alignment state at high speed in order to realize the alignment state shown in FIG. R0, R1, R2, and R3 indicate pixel lines of the display, and the line refers to a row of pixels selected by a common data electrode. FIG. 2 shows the type of voltage applied to each line and the application period. Hereinafter, the embodiment will be described with respect to a scan electrode side driver connected to the scan electrode.

  The period in which the voltage is applied to each line is classified into four types, a non-selection period, a preparation period, a selection period, and an evolution period, depending on how the voltage is applied. The non-selection period is a period in which a voltage that does not change the state of the liquid crystal is applied, and the preparation period is a period in which a voltage that brings the liquid crystal into a homeotropic alignment state is applied.

  The selection period is a period during which a voltage for transitioning the liquid crystal once in the homeotropic alignment state to the focal conic alignment or the planar alignment is applied. The evolution period is a period in which a voltage is applied so as to fix the liquid crystal state changed from homeotropic alignment to focal conic alignment or planar alignment.

  FIG. 3 is a diagram for explaining the voltage applied to the scan electrode side in each period. The driver for an image display device according to the present embodiment applies to each of a plurality of scan electrodes while switching one of the voltages set in multiple levels (eight levels in the present embodiment) every predetermined voltage application period. is there. Similarly, a predetermined voltage is applied to the data electrode side. Such a voltage application method is called so-called DDS driving.

In the voltage pattern shown in FIG. 3, (a) is a voltage pattern applied during the preparation period, and the voltage of V1 and V8 is the voltage of the A section and the B section, the C section and the D section. It is applied to the scan electrode while switching every application period.
(B) is a pattern of voltages applied during the Selection period, and this pattern applies the voltages of V5, V8, V1, and V4 to the four voltages in the A section, B section, C section, and D section. It is applied to the scan electrode while switching every period. (C) is a pattern of voltages applied during the evolution period. This pattern is applied to the scan electrodes while switching the voltages V3 and V6 for each voltage application period of the A section, the B section, the C section, and the D section. To be applied.

Further, FIG. 3D shows a pattern of voltages applied during the non-selection period. This pattern is obtained by changing the voltages of V7 and V2 for each of the voltage application periods of the A section and the B section, the C section, and the D section. It is applied to the scanning electrode while switching to
In addition, on the data electrode side, a predetermined voltage is applied while switching every voltage application period of A section, B section, C section, and D section, and a predetermined voltage is applied to the liquid crystal by a combination of the scan electrode and the data electrode. is doing.

  By the way, the line of a plurality of pixels constituting the display is in any one of four periods of a non-selection period, a preparation period, a selection period, and an evolution period while the driver is driving. Therefore, according to FIG. 3, for example, in section A, V1 (FIG. 3 (a)), V5 (FIG. 3 (b)), V3 (FIG. 3 (c)), V7 are applied to all lines of the display. It can be seen that any one of the voltages shown in FIG. 3 (d) is applied.

Further, according to FIG. 3, in the section B, V1 (FIG. 3A), V8 (FIG. 3B), V3 (FIG. 3C), V7 (FIG. 3 (d)) is applied.
In section C, V8 (FIG. 3 (a)), V1 (FIG. 3 (b)), V6 (FIG. 3 (c)), V2 (FIG. 3 (d)) for all lines of the display. One of the voltages is applied. Further, in section D, V8 (FIG. 3 (a)), V4 (FIG. 3 (b)), V6 (FIG. 3 (c)), and V2 (FIG. 3 (d)) are applied to all lines of the display. It can be seen that either voltage is applied.

  That is, the DDS drive driver drives the scan electrodes of the display using eight voltage values, but only four of them are used in one voltage application period. In this embodiment, paying attention to this point, four voltage values used in each of the sections A to D shown in FIG. 3 are selected in advance from eight voltage values, and only the selected four voltage values are selected. Is a driver for an image display device configured to be usable.

  In this embodiment, the number of level shifters need only be the number corresponding to the number of four voltage values used in each of the sections A to D. Therefore, the number of level shifters can be reduced as compared with the conventional configuration in which eight voltage values are selected using eight level shifters for each line, and thus the area of the driver chip can be reduced.

  FIG. 4 is a diagram for explaining the configuration of the image display device driver of the present embodiment. The illustrated driver is a display driver that changes the alignment state of the cholesteric liquid crystal by applying a voltage to the scanning electrode 407 by DDS driving. The illustrated driver includes a section selection circuit 402 for inputting section information (sections A to D in FIG. 3) concerning a voltage application period, and section information indicates a plurality of voltage values set in eight stages based on the section information. A supply voltage selection unit 401 that selects a voltage value applied to the scan electrode 407 in the section is provided.

  The driver illustrated in FIG. 4 includes a level shifter and output transistor unit 406 that generates a pulse voltage having a voltage value selected by the supply voltage selection unit 401 and applies the pulse voltage to the scan electrode 407. The configuration denoted by reference numeral 405 in the figure is a level shifter unit including a plurality of level shifters. The level shifter unit 405 includes level shifters 405a to 405d corresponding to the number of voltage values selected by the supply voltage selection unit 401 (four in this embodiment).

  In addition, the driver of this embodiment includes a voltage selection unit 404 that allows a predetermined voltage value to be selected from the voltage value generated by the supply voltage selection unit 401 through the level shifters 405a to 405d. The level shifters 405a to 405d are configured to pull up the voltage selection signal selected by the voltage selection unit 404 from the lowV system signal to the highV system signal, and the voltage value of the voltage selection signal input from the voltage selection unit 404 is highV. It is possible to turn on / off the transistor of the output transistor unit by converting into a system.

The voltage selection unit 404, the level shifter unit 405 (level shifters 405a to 405d), and the output transistor unit 406 each correspond to the scan electrode 407, and n each is provided when the scan electrode 407 has n lines.
In the above configuration, the section selection circuit 402 functions as period information input means. The supply voltage selection unit 401 functions as a voltage selection unit, and the voltage selection unit 404, the level shifters 405a to 405d, and the output transistor unit 406 function as a voltage application unit. Of the voltage application means, the output transistor unit 406 serves as voltage output means for outputting a pulse voltage of the selected voltage value based on the value of the voltage selection signal converted by the level shifters 405a to 405d.

  Furthermore, the driver of this embodiment includes a logic unit 403. The logic unit 403 inputs serial data (denoted as display control data) for determining whether each line exists in any of the preparation period, the selection period, the evolution period, and the non-selection period shown in FIG. This is a serial-parallel conversion device that outputs in parallel to a plurality of voltage selection units 404 corresponding to the number of scan electrodes.

  FIG. 5 is a diagram for explaining the section selection circuit 402 and the supply voltage selection unit 401 shown in FIG. 4 in more detail. The section information is input to the section selection circuit 402 as d1 and d2 data by a display control unit (not shown) that generates display control data. Data d1 and data d2 are both 1 or 0 data, and can represent a total of four sections A to D.

  In addition, the section selection circuit 402 includes a table 501 that describes four-level voltage values corresponding to each of the sections A to D. The table 501 is a table that records the relationship between each section described in FIG. 3 and the voltage value that can be applied to the scan electrode 407 simultaneously in each section. For example, when d1 and d2 indicating the section A are input, the section selection circuit 402 outputs a selection signal for selecting the voltages V1, V3, V5, and V7 to the supply voltage selection unit 401. The supply voltage selection unit 401 includes four voltage selection Tr units 502.

  FIG. 6 is a diagram for explaining the voltage selection Tr unit 502 shown in FIG. The voltage selection unit Tr502 includes eight transistors that can select different voltage values from among the eight levels of voltage according to the voltage selection signal input from the section selection circuit 402. It should be noted that the voltage selection Tr unit 502 must turn on the transistor corresponding to the eight levels of voltage values. Therefore, according to the voltage range of the selection voltage value, in this embodiment, the voltage selection Tr unit 502 is configured by mixing p-channel transistors and n-channel transistors. For example, when a low voltage value is selected, only an n-channel transistor is selected. When a high voltage value is selected, only a p-channel transistor is selected. When an intermediate voltage is selected, an n-channel transistor is selected. This is realized by a p-channel transistor transmission structure.

When a selection signal for selecting, for example, V1 is input to the voltage selection Tr unit 502, only the transistor corresponding to V1 among the eight transistors is turned on. When the transistor corresponding to V1 is turned on, V1 is supplied to the output transistor unit 406 as one of four selectable output voltages.
In the driver of the present embodiment, the above-described configuration is provided on the wafer 408 to form an integrated chip. Each of the section selection circuit 402 and the supply voltage selection unit 401 has a hardware configuration and is fixed on the wafer 408.

The configuration described above operates as follows. That is, when the driver of the present embodiment starts operation, the section information d 1 and d 2 are input to the section selection circuit 402. Further, a voltage signal having values of V1 to V8 in accordance with the DDS standard is input to the supply voltage selection unit 401.
The section selection circuit 402 determines a section for voltage application based on the section information d1 and d2. Then, four-level voltage values that are simultaneously used in the corresponding section determined by the table 501 are determined, and four selection signals for selecting these voltages are output to the supply voltage selection unit 401.

The supply voltage selection unit 401 receives a signal indicating a 4-level voltage value, and selects a 4-level voltage from the input 8-level voltage. Then, the output transistor unit 406 is controlled to output the selected four-level voltage value.
Further, the voltage selection unit 404 outputs a voltage selection signal to be output to the level shifter unit 405 according to the contents of the table 501 in the supply voltage selection unit 401. The level shifters 405a to 405d of the level shifter unit 405 convert the input voltage selection signal into a highV system and output it to the output transistor unit 406, so that any one of the four level voltage values can be selected.

  As a result, the selection voltage signal converted by the level shifters 405a to 405d is input to each transistor capable of selecting the four-level voltage selected by the supply voltage selection unit 401 in the output transistor unit 406. The transistor of the output transistor unit 406 turns on the transistor corresponding to the output voltage based on the input selection voltage signal and applies the selected voltage to the scan electrode 407.

  According to this embodiment described above, 8-level voltage values for DDS driving can be output by the same number of level shifters as the number of voltage values used in one section. The configuration of the present embodiment can be realized by adding one supply voltage unit 401 and one section selection circuit 402 to the driver. In this embodiment, the area of the driver for the image display device can be reduced as compared with the conventional configuration in which eight level shifters are provided for each output line.

More specifically, in a driver for DDS driving a cholesteric liquid crystal, the area of a level shifter of a driver having four level shifters is about 50% of that having eight level shifters, depending on the area of the logic circuit, etc. A large area reduction can be realized.
Note that the driver of the present embodiment is not limited to the configuration described above. For example, when there is a voltage value used in all of the sections A to D (for example, when V1 and V8 are necessary in all the sections), only this voltage does not pass through the supply voltage selection unit 401 or the section selection circuit 402. You may make it supply to the output transistor part 406 directly.

  In the present embodiment, a display using a cholesteric liquid crystal is DDS-driven as an example. However, the present embodiment is not limited to such a configuration, and can be applied to a display using other memory liquid crystal. In DDS driving, the voltage value and voltage value configuration in the preparation period, etc., are changed within a range that does not deviate from the concept of DDS driving (for example, in the preparation period, a voltage capable of transitioning to homeotropic orientation is applied). However, the present embodiment can also be applied to such a case.

It is a figure for demonstrating the orientation state of the cholesteric liquid crystal in a common display. FIG. 2 is a diagram showing voltage application timings in DDS driving that enables high-speed transition of the alignment state shown in FIG. It is a figure for demonstrating the voltage applied in each period shown in FIG. It is a figure for demonstrating the structure of the driver for image display apparatuses of one Embodiment of this invention. FIG. 5 is a diagram for explaining the section selection circuit and the supply voltage selection unit shown in FIG. 4 in more detail. It is a figure for demonstrating the voltage selection Tr part shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate, 2 Light absorption layer, 3 Transparent electrode, 4 Cholesteric liquid crystal, 401 Supply voltage selection part, 402 Section selection circuit, 403 Logic part, 404 Voltage selection part, 405 Level shifter unit, 405a-405d Level shifter, 406 Output transistor part 407 Scan electrode 408 Wafer 501 Table 502 Voltage selection Tr section

Claims (2)

An image display device that changes the alignment state of a liquid crystal to which a voltage is applied by switching one of voltages set in multiple stages to each of a plurality of data electrodes or a plurality of scanning electrodes while switching every predetermined voltage application period Driver,
Period information input means for inputting information relating to the voltage application period;
Based on the period information input by the period information input means, a voltage value applied to the data electrode or the scan electrode during a period indicated by the period information is selected from a plurality of voltage values set in multiple stages. Voltage selection means;
Voltage application means for generating a pulse voltage having a voltage value selected by the voltage selection means and applying the pulse voltage to the data electrode or the scan electrode;
A driver for an image display device, comprising: The voltage applying means includes
A number of level shifters corresponding to the number of voltage values selected by the voltage selection means;
Voltage output means for outputting a pulse voltage of a voltage value selected based on a signal for selecting a predetermined voltage value converted by the level shifter;
The image display device driver according to claim 1, further comprising:

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