JPH1184344A - Driving method for liquid crystal device and electronic equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the irregularity of display and the variance of threshold values caused by the flowing of liquid crystal molecules in a liquid crystal layer when a voltage is impressed by scanning a scanning electrode from the scanning electrode positioned on an opposite side of a part where a data electrode driving means is arranged. SOLUTION: This device is provided with a first and a second Y driver circuits 11A and 11B being as the scanning electrode driving means and a first and a second X driver circuits 12A and 12B being as the signal electrode driving means connected to the lower side of a liquid crystal panel 10 in order to drive the panel 10. The scanning of the scanning electrode (Y electrode) is executed from the upper edge of the panel and the line sequential scanning is executed toward an X driver 12 on the lower side. When the line sequential scanning is executed toward the lower part from the upper part, liquid crystal is also moved in a scanning direction and moved in the direction of a synthesized vector as the result. By impressing scanning driving waveform to be impressed on the scanning electrode from the scanning electrode being distant from the driver circuits 12A and 12B, the liquid crystal molecules are prevented from flowing in the panel 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for driving a liquid crystal device. More specifically, the present invention relates to a driving method and a driving circuit for a bistable liquid crystal display device (binary twisted nematic liquid crystal = BTN) using a chiral nematic liquid crystal.

[0002]

2. Description of the Related Art The inventors of the present invention applied for a liquid crystal display device having a bistability using a chiral nematic liquid crystal (or simply referred to as a liquid crystal) and filed Japanese Patent Application Laid-Open Nos. 06-230751 and 07-175041. Liquid crystal display device and its driving method have been realized. That is, a chiral nematic liquid crystal having an initial twist angle Φ (for example, 180 degrees) is arranged between upper and lower glass substrates on which strip-shaped electrodes for forming a matrix display are arranged, and the liquid crystal molecules stand vertically between the upper and lower electrodes. After applying a sufficient giant pulse to the liquid crystal, an appropriate delay time is provided, and then a selection pulse is applied to the liquid crystal at the boundary of the threshold value, and the untwisted 0 degree uniform state (Φ-180 degrees) is obtained. The present invention provides a display device in which a twisted 360 ° (Φ + 180 °) twisted state is formed and the display is turned ON or OFF.

FIG. 9 is an example of a block diagram showing the entire configuration of the display device. The liquid crystal panel 10 is 320 ×
The liquid crystal panel 10 has 240 pixels, and is provided with first and second Y driver circuits 11A and 11B and first and second X drivers 12A and 12B to drive the liquid crystal panel 10. The first and second Y driver circuits 11A and 11B have the same configuration, and details thereof are shown in FIG.
Further, the X drivers 12A and 12B have the same configuration, and details thereof are shown in FIG.

In the ordinary matrix driving of the above configuration, the Y driver 11 sequentially outputs selected waveforms from top to bottom, and performs line scanning from COM0 to COM239. Further, a data signal is output from the X driver 12 in synchronization with the selected waveform to obtain a desired display.
However, it has been found that when an image is displayed by the above-mentioned bistable (BTN) liquid crystal display by such a scanning method, display unevenness or display failure is likely to occur in a portion along the lower side of the display panel 10. . Then, the present inventor sets S
The method of obtaining a uniform image, which has been tried with TN liquid crystal or FLC (ferroelectric liquid crystal), was applied to BTN.
A problem arises in that the driving problems of the TN and the response speed are adversely affected. One of them is a method disclosed in Japanese Patent Application Laid-Open No. Sho 62-156623 in which the scanning direction is switched at predetermined intervals. In the case of this method, in the BTN, when the scanning direction is switched, the row electrode at the end is continuously in the selection period. Therefore, there is no time to input a reset pulse preceding the selection period, and the beginning of the frame in which the scanning direction is reversed is eliminated. Indicates ON / OFF of display
Switching has been disabled. Also, at the end of the previous frame, the next selected waveform enters the optical response, the response was interrupted, and the display state was incomplete.
As a result, large flickers occur in specific portions above and below the display panel, and display quality is degraded.

[0005] The second is to reverse the scanning direction in the odd-numbered and even-numbered scanning electrodes disclosed in Japanese Patent Application Laid-Open No. 62-156624. There is a time difference between the image composed of the odd-numbered electrodes and the image composed of the even-numbered electrodes.
It is visualized as an image with striped patterns. Considering this from the viewpoint of a person who actually uses the liquid crystal display, every time the user moves his / her eyes, very obtrusive stripes are seen, which is a major application problem. Third, in the case of FLC, one screen in Japanese Patent Laid-Open No. 05-303076 is divided into a predetermined number, and the scanning direction of each block in one frame is made reverse to the scanning direction of the other blocks, thereby causing flicker. And so on to improve image quality. But B
In the TN reflection type liquid crystal display, because of the presence of the reset pulse and the high optical response, the stripe flow moving in the opposite direction for each block could not be eliminated, and the display quality did not improve.

[0006]

As described above, in the BTN, it has been found that the above-mentioned problems of the color unevenness and the display failure cannot be solved only by following the image quality improvement measures taken by the conventional STN and FLC. This is because the BTN is a display based on a principle different from that of the conventional liquid crystal, the factors causing color unevenness and the like are different, and the driving method is a display device different from other liquid crystal displays. The present invention provides a method for eliminating color unevenness or display failure suitable for BTN based on the above results.

[0007]

According to the present invention, there is provided a driving method of a liquid crystal device having a liquid crystal layer sandwiched between a pair of opposing substrates, wherein the liquid crystal layer has an initial state in which a twist angle of liquid crystal molecules is Φ. The alignment state of the liquid crystal molecules is approximately Φ-180.
And a second stable state in which the alignment state of the liquid crystal molecules is substantially Φ + 180 degrees, and a scan applied to a plurality of scan electrodes formed on one substrate. A signal and a data signal applied to a plurality of data electrodes formed on the other substrate, controlling an alignment state of the liquid crystal layer, and a scanning electrode driving unit is connected to the scanning electrode, The data electrodes are connected to data electrode driving means, and the scanning electrodes are scanned from the scanning electrodes located on the side opposite to the side on which the data electrode driving means is arranged.

With this configuration, it is possible to eliminate display unevenness and threshold unevenness caused by the flow of liquid crystal molecules in the liquid crystal layer due to voltage application.

The scanning of the scanning electrodes can be performed by line-sequential scanning, or a driving method of simultaneously selecting a plurality of scanning electrodes may be used. In particular, by adopting a driving method of simultaneously selecting a plurality of lines, high-speed driving without display unevenness can be realized. Note that a liquid crystal device driven by such a driving method can be mounted on an electronic device.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before entering into a concrete embodiment, the reason for the above-mentioned problem solving means will be described.

(Principle and operation) The present inventors have confirmed that the liquid crystal in the panel moves in the development stage of the liquid crystal display using BTN. FIG. 6 shows the moving direction of the liquid crystal in the case of the matrix display. Assuming that the rubbing direction in the panel is the vertical direction parallel to the short side of the panel, the initial orientation direction of the substrate interface is limited to this, and a 180 degree twist state (generally indicated as Φ), the rubbing state is in the display driving state. The simulation revealed that liquid crystal molecules move to the right, perpendicular to the direction. When the matrix-driven line-sequential scanning is performed from top to bottom, the liquid crystal also moves in the scanning direction, and as a result, it is thought that the liquid crystal moves in the vector direction. For this reason, it was recognized that the cell thickness was increased along the lower side of the display panel, and the threshold of the driving voltage was increased. Also,
Since the location of the moved liquid crystal disappears in the vicinity of the seal, it is considered that this also causes some operation hindrance in the BTN utilizing the flow of the liquid crystal.

On the other hand, BTN is different from the conventional liquid crystal display element and responds to a drive pulse, so it has been found that the BTN is severe against waveform dulling. Therefore, it was also recognized that the driving margin was reduced in a place far from the driver where the electrode resistance increased. In other words, it can be understood that if the liquid crystal is driven with the current driver arrangement, the disadvantageous condition overlaps with the lower side of the panel, and it is difficult to obtain a uniform display.

In the present invention, in order to avoid this, the scanning direction is set as described above in order to bring the movement of the liquid crystal closer to the driver which is less affected by the waveform dulling. In this way, even if the cell thickness increases due to the movement of the liquid crystal and the threshold value rises, a drive waveform with less waveform dullness enters the cell, so that a decrease in margin can be suppressed as much as possible.

Embodiment 1 FIG. 1 is a block diagram showing a configuration of a liquid crystal display device according to the present invention. The liquid crystal panel 10 has 320 × 240 pixels.
To drive the first and second Y driver circuits 11A and 11B as scanning electrode driving means and the first and second X as signal electrode driving means connected to the lower side of the panel.
Driver circuits 12A and 12B are provided. First,
The second Y driver circuits 11A and 11B have the same configuration, and details thereof are shown in FIG. The X driver circuits 12A and 12B also have the same configuration, and the details are shown in FIG.

In the display device having such a configuration, in the present invention, scanning of the scanning electrodes (Y electrodes) is performed from the upper end of the panel, and line-sequential scanning is performed toward the X driver 12 on the lower side. At this time, since the X driver 12 is in a positional relationship of being rotated by 180 degrees with the conventional example, the output of the data signal must be reversed in order to obtain the same erect image.

FIG. 2 is a block diagram showing details of the Y driver circuit used in the above embodiment, and FIG. 7 is a timing chart for explaining the operation of this driver circuit. The Y driver circuit 11 has a shift register for selection 13A and a shift register for reset 13B having 120 stages of registers. A reset signal RI specifying a reset period is input to the reset shift register 13A, and is sequentially shifted to the next-stage register by the shift clock YSCK. Further, a select signal SI specifying a select period is input to the select shift register 13B, and this is also sequentially shifted to the next register by the shift clock YSCK. The contents of the register at the final stage are output via the output terminals RO and SO.
The cascade connection with the second Y driver 11B is enabled. Since the reset and select shift registers 13A and 13B have a bidirectional function, the shift direction of the registers can be reversed by designating the external control signal L / R. Next, the contents in each of the shift registers 13A and 13B are input to the output control circuit 14 in parallel for all 120 channels. Output control circuit 14
Is a reset signal R, a select signal S, and an AC signal F
There are six states depending on the input state of R, that is, R, S, FR.
= (0, 0, 0) or (0, 0, 1) or (0,
(1, 0) or (0, 1, 1) or (1, 0, 0) or a signal that distinguishes (1, 0, 1) is output to the COM driver 16 via the level shifter 15. Is done. Five kinds of driving voltages ± Vr, ± Vs, 0 are input to the driver 16, and based on the six states that are output separately from the output control circuit 14,
Any one drive voltage is output for each channel. Next, details of the X driver circuit 12 for applying a signal to the data electrode (X electrode) will be described with reference to FIGS.
This will be described with reference to FIG. This first X driver circuit 12
A is a shift register 17 having 160 registers.
And sequentially shifts the input signal EI to the next-stage register according to the shift clock XSCK. The contents of the 160th register are output to the outside via the EO terminal,
Used for cascade connection with the second X driver circuit 12B. The shift register is bidirectional, and can be shifted in the opposite direction by an external input signal L / R. In the embodiment shown in FIG. 1, the shift direction must be set opposite to the normal setting.

The signal E input to the shift register 17
I is a signal that becomes logic 1 once in one horizontal scanning period (1H). Therefore, the first latch circuit A1 is synchronized with the timing when each register of the shift register 17 becomes logic 1.
Reference numeral 8 latches image data at a corresponding address. That is, image data for 160 columns × 1 row can be latched by one driver. This latch data is transferred to the second latch circuit B19 in synchronization with another X driver at the timing when another latch pulse LP is input. In this embodiment, since there are two X drivers of 12A and 12B, data of 320 columns × 1 row is simultaneously moved to the latch circuit B19. AC signal FR
The output control circuit 20 that inputs the data from the latch circuit B19 has four states (D, FR) = (0, 0) according to the input state of the data D and the AC conversion signal FR.
Alternatively, a signal that distinguishes (0, 1) or (1, 0) or (1, 1) is input to the SEG driver 22 for each channel via the level shifter 21. The SEG driver 22 has two types of drive voltages ± Vd, and outputs one of the two types of drive voltages for each channel based on a signal from the output control circuit 21.

FIG. 10 shows an example of typical driving waveforms of a BTN liquid crystal display obtained by the above driving circuit. Yk
Is a scan driving waveform, Xl is a data waveform, and the differential waveform applied to the liquid crystal is Yk-Xl at the bottom.

By applying the above-described scanning drive waveform applied to the scanning electrodes from the scanning electrode far from the X driver circuit, it is possible to prevent the flow of liquid crystal molecules generated in the liquid crystal layer in the liquid crystal panel. Thus, a liquid crystal panel (liquid crystal device) without display unevenness can be obtained.

The scanning method of the scanning electrodes may be line-sequential driving or interlace driving. Further, it is also possible to use a driving method adopting the concept of so-called MLS driving in which a plurality of scanning electrodes are simultaneously selected and each group is sequentially selected. When the MLS driving method is adopted in the liquid crystal device of the present invention, it is necessary to appropriately set the selection voltage applied to the scanning electrodes according to the number of scanning electrodes to be simultaneously selected. That is, MLS using a normal STN liquid crystal
Since the driving method is completely different from the driving method, in the driving method of the so-called BTN liquid crystal device of the present invention, the setting is appropriately made by paying attention to the selection voltage.

(Embodiment 2) FIG. 4 shows another embodiment of the present invention. The difference from the embodiment of FIG.
A, 11B. That is, the Y driver was installed on the right side of the display panel where an erect image could be formed. In this case, the Y drivers 11A and 11B are turned by 180 degrees as compared with the case of FIG.
It is necessary to reverse by the / R terminal. By doing so, the line-sequential scanning direction can be performed from top to bottom toward the X drivers 12A and 12B. The X driver may be the same as in FIG.

(Embodiment 3) FIG. 5 shows still another embodiment of the present invention. The arrangement of the X driver and the Y driver is the same as in the conventional example. However, the line sequential scanning direction of the Y driver 11 is a reverse shift from the bottom to the top of the panel. In order to obtain an erect image when line-sequential scanning is performed toward the X drivers 12A and 12B in this arrangement, image data to be displayed is read from the bottom row of the display panel 10 and data in the upper row is sequentially read from the X driver. 12 must be output. For that purpose, it is necessary to prepare the frame memory 23 as shown in FIG. 5 and to read the erect image data once read from the last data. The output Data from the frame memory is the data input Da to the X driver
If ta is set, the other operations are the same as those described above. As described above, since this embodiment requires a frame memory in addition to the conventional driver configuration, it will be an extremely limited application. It is also possible to arrange the Y driver 11 on the right side of the panel 10. In this case, the shift direction of the register may be set to the original positive direction. Embodiment 4 FIG. 11 is an external view showing an example of an electronic apparatus using the liquid crystal device of the present invention. In this embodiment, an example in which the liquid crystal device is mounted on an electronic device as a reflective liquid crystal panel will be described. Since the liquid crystal panel is a reflection type liquid crystal panel, it has reflection means such as a reflection layer and a reflection electrode on the back surface of the liquid crystal panel or on the inner surface of the substrate.

FIG. 11A is a perspective view showing a mobile phone. 1000 denotes a mobile phone body, of which 100
Reference numeral 1 denotes a liquid crystal display unit using the reflection type liquid crystal panel of the present invention.

FIG. 11B is a diagram showing a wristwatch-type electronic device. 1100 is a perspective view showing the watch main body. 1
Reference numeral 101 denotes a liquid crystal display unit using the reflection type liquid crystal panel of the present invention. Since this liquid crystal panel has higher definition pixels than a conventional clock display unit, it can also display television images, and can realize a wristwatch type television.

FIG. 11C shows a portable information processing apparatus such as a word processor or a personal computer. 1200 denotes an information processing device, 1202 denotes an input unit such as a keyboard,
Reference numeral 06 denotes a display unit using the reflective liquid crystal panel of the present invention.
Reference numeral 04 denotes an information processing apparatus main body. Since each electronic device is a battery-driven electronic device, the use of a reflective liquid crystal panel without a light source lamp can extend the battery life.

Although an application example has been described as a portable electronic device as described above, the invention can also be applied to a projector by using a liquid crystal device as a light valve.

[0027]

As is apparent from the above description, the present invention provides a bistable liquid crystal display using a chiral nematic liquid crystal, in which the line-sequential scanning direction of matrix driving is set to a direction going toward the X driver. Thus, it is possible to eliminate color unevenness, threshold unevenness, and display defects in the panel surface. As a result, the quality of the present liquid crystal display device is further improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a liquid crystal display device according to the present invention.

FIG. 2 is a detailed configuration diagram of a Y driver circuit.

FIG. 3 is a detailed configuration diagram of an X driver circuit.

FIG. 4 is a configuration diagram of a liquid crystal display device showing another embodiment of the present invention.

FIG. 5 is a configuration diagram of a liquid crystal display device showing still another embodiment of the present invention.

FIG. 6 is a schematic diagram for explaining the principle of the present invention.

FIG. 7 is a timing chart of a Y driver.

FIG. 8 is a timing chart of an X driver.

FIG. 9 is a configuration diagram of a conventional liquid crystal display device.

FIG. 10 is a typical drive waveform diagram of a BTN liquid crystal display.

FIG. 11 illustrates a specific example in which a liquid crystal device is mounted on an electronic device.

[Explanation of symbols]

 Reference Signs List 10 liquid crystal display panel 11 Y driver 12 X driver 13 shift register 14 COM output controller 15 level shifter 16 COM driver 17 bidirectional shift register 18 data latch 19 latch 20 SEG output controller 21 level shifter 22 SEG driver T1 reset period T2 delay period T3 selection period T4 non-selection period

Claims (4)

[Claims] In a driving method of a liquid crystal device in which a liquid crystal layer is sandwiched between a pair of opposed substrates, the liquid crystal layer has an initial state in which a twist angle of liquid crystal molecules is Φ and an alignment state of the liquid crystal molecules. A plurality of scanning electrodes formed on one substrate have at least a first stable state of approximately Φ−180 degrees and a second stable state of approximately Φ + 180 degrees of alignment of the liquid crystal molecules. An applied scanning signal and a data signal applied to a plurality of data electrodes formed on the other substrate control an alignment state of the liquid crystal layer,
Scan electrode driving means is connected to the scan electrode,
A liquid crystal device, wherein a data electrode driving means is connected to the data electrode, and the scanning electrode scans from the scanning electrode located on a side opposite to a side on which the data electrode driving means is arranged. Drive method. 2. A driving method for a liquid crystal device according to claim 1, wherein the scanning of said scanning electrodes is performed in a line-sequential manner. 3. A driving method for a liquid crystal device according to claim 1, wherein a plurality of scanning electrodes are simultaneously selected for scanning the scanning electrodes. 4. An electronic apparatus equipped with a liquid crystal device driven by the driving method according to claim 1.