JPS62134630A - Method for driving liquid crystal display device - Google Patents

Abstract

PURPOSE:To eliminate the variation of contrast on boundaries by dividing a display screen into plural areas and providing n-number of scanning electrodes in each area and impressing a voltage having a duty ratio lower than 1/n and using the margin of time to switch the voltage polarity before the next scanning start after the first - the n-th scannings are performed. CONSTITUTION:In case of scanning of a liquid crystal display device of 200X640 dots, scanning lines are vertically driven by 100 lines and are driven. At this time, the duty ratio is set to 1/120, and the time required for one circulation of voltage impression to 100 scanning electrodes in a display area is shortened to 100/102 of the normal time. Thus, the margin of time of 2/102 is generated before voltage impression to the first scanning electrode of the next frame is started after the end of voltage application to one frame. This margin of time is used to switch the polarity of the impressed voltage, and the switching time and the scanning start time do not overlap to make the variation of contrast on boundaries inconspicuous.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a liquid crystal display device in which a display screen is divided into a plurality of display areas. The present invention relates to a method for driving a liquid crystal display device that does not produce a display with a contrast different from that of the above part and provides a display with a good display quality.

<Prior Art> As is well known, driving a liquid crystal display device with direct current induces an electrochemical reaction inside the liquid crystal cell, which significantly shortens the life of the display device. Therefore, it is necessary to change the polarity of the voltage applied to the liquid crystal cell. It is reversed at appropriate intervals.

As a method for reversing the polarity of this applied voltage, there have been used a method in which the polarity is changed to alternating current for each scanning line, and a method in which the polarity is changed to alternating current in two frames. Furthermore, as large liquid crystal display devices are used and the number of time divisions increases, the latter is becoming mainstream (1 Nikkei Electronics J, August 1980).
8th issue).

Conventionally, in the case of n scanning electrodes for one display area, scanning was performed at a duty ratio of 1/n. Move the display area up and down 2
Taking as an example the case of the driving method in which the driving method is divided into two frames and converted to AC in the two frames described above, the timing of applying the scanning voltage to the first scanning bridge in each of the upper and lower display areas, and the timing of applying the scanning voltage to the first scanning bridge in each of the upper and lower display areas, and the timing of applying the scanning voltage to the liquid crystal cell of each display area. This coincides with the timing of switching the polarity of the applied voltage at the first scanning electrode, and the electrode voltage changes drastically when voltage is applied to the first scanning electrode. The voltage becomes larger than when the voltage is applied to the second and subsequent scan electrodes. Therefore,
Particularly in the case of full-screen display or full-screen white display, there has been a problem in that the contrast is different at the boundaries of these display areas compared to other areas, resulting in a reduction in display quality.

<Problems to be Solved by the Invention> As described above, the present invention aims to solve the conventional problem of noticeable changes in the contrast of scanning lines at the boundaries of display areas. do.

Means for Solving the Problems In order to achieve the above object, the present invention provides a liquid crystal display device in which a display screen is divided into a plurality of display areas, and each area is provided with n scanning electrodes. Scanning is performed by applying a voltage with a duty ratio shorter than l/n to each electrode, and voltage is sequentially applied from the first to the nth scanning electrode in a certain display area to finish scanning that display area. Thereafter, the polarity of the voltage applied to the liquid crystal is switched within the remaining time created by the shortening of the duty ratio until the start of the next scan.

<Operation> Conventionally, the duty ratio during actual scanning was reduced to 1/n.
(However, n is the number of scan electrodes provided in one display area) If we change it to 1/(n+m) (however, m is a smaller integer than n), the voltage is applied to the first scan electrode. The time required from the start of the voltage application to the end of the voltage application to the n-th scan electrode is shorter than the time conventionally required for one cycle of voltage application to all the scan electrodes in one display area ( Become.

Therefore, in the case of the present invention, if the time from the start of scanning of a certain frame to the start of the next frame is the same as before, the time when voltage application to the last scanning electrode of a certain frame in a certain display area ends. There is a longer idle time than in the conventional case between this time and the time when voltage application to the first scanning electrode is started in the next frame. This time is just like the retrace time in the case of a television, and in the present invention, the polarity of the voltage applied to the liquid crystal cell is switched within this free time, and the polarity of the voltage applied to the liquid crystal cell is switched to the first scanning electrode of the next frame. The timing at which the scanning voltage is applied to the cell does not overlap with the timing at which the polarity of the voltage applied to the cell is switched, so that fluctuations in the voltage level of this first scanning electrode do not become as large as in the conventional case. be. In this way, the voltage fluctuation when applying the scanning voltage to the first scanning electrode at the boundary of the display area will be the same as when applying the scanning voltage to the other scanning electrodes, and the contrast will be particularly noticeable. That half will not survive.

<Example> Hereinafter, an example of the present invention will be described with reference to FIGS. 1(a), (b), <c
> will be explained. This liquid crystal display device has 200
It is assumed that 640 dots are driven in upper and lower halves of 100 scanning lines each. If the duty ratio is 1/102 (i.e., n = 100, l'l'l = 2), the time required to apply voltage to 100 scan electrodes in the display area once is 100/102 compared to the conventional one. From this end time to the time when voltage application to the first scanning electrode is started for the next frame, there is a margin time of 2/102 of the conventional scanning time for one display area. occurs. In this embodiment, the polarity of the voltage applied to the liquid crystal cell is switched in the middle of this margin time, when 101/102 of the conventional scan-delay time has elapsed, and the start of scanning for the next frame is the same as in the conventional case. Do it at the right time.

FIG. 1(a) shows a display area scanning start signal.

FIG. 1(b) shows a signal for latching, in the launch circuit, data to be displayed corresponding to the -scanning line on the opposing signal electrodes crossing the scanning electrodes.

Figure 1(C) shows the signals for reversing the polarity of the voltage applied to the cell, and from these figures it can be seen that the reversal of the polarity of the voltage applied to the cell ends before the start of scanning for the next frame. I can see that you are doing it.

<Effects of the Invention> As explained above, according to the present invention, the timing of switching the polarity of the voltage applied to the liquid crystal cell and the timing of starting scanning of the display area do not overlap, so that the display of a liquid crystal display device having a plurality of display areas is improved. There are no problems such as noticeable contrast fluctuations at the boundaries of regions.

[Brief explanation of drawings]

FIG. 1(a) is a diagram showing a scanning start signal according to an embodiment of the present invention;
FIG. 1(b) shows a signal for latching data for each scanning line in the same embodiment, and FIG. 1(c) shows a signal for switching the polarity of the voltage applied to the cell in the same embodiment. It is a diagram.

Claims (1)

[Claims] The display screen is divided into a plurality of display areas in the scanning direction, and each electrode of a liquid crystal display device is provided with n scanning electrodes in each area, and each electrode is scanned by applying a voltage with a duty ratio shorter than 1/n. , after the end of scanning from the first to nth scanning electrodes in a certain display area, the polarity of the voltage applied to the liquid crystal is switched within the remaining time caused by the above duty ratio reduction until the start of the next scanning. A method for driving a liquid crystal display device, characterized in that: