JPS6318332A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To eliminate irregularity in display by supplying an AC converted signal and a signal obtained by dividing the frequency of a strobe signal optionally to an exclusive OR gate and generating an AC-converted signal having a shorter period than said AC-converted signal. CONSTITUTION:A signal (FRM signal) which serves as both a frame scanning period signal and an AC-converted period signal is separated into a frame scan start command signal (FLM signal) 6 and an AC-converted signal M through a D flip-flop 1, the exclusive OR gate 2, and an inverter 4. Strobe signals STB which are outputted by as many as scanning electrodes within one frame period are frequency-divided by a counter 3 optionally and properly and this frequency-divided signal and the AC-converted signal M outputted from an integrated circuit for display device control are inputted to the one exclusive OR gate 2 to generate the short cycle AC-converted signal M' obtained by inverting the original AC-converted signal M more than once in the middle of the original cycle with the frequency-divided signal of the strobe signals. Consequently, the polarity of an electrode-applied voltage is inverted in polarity more than once in the middle of the scanning period of a certain frame and the irregularity in display is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a dot matrix type liquid crystal display element that is capable of providing an easy-to-see and pleasant display with little unevenness in display density.

[Conventional technology]

In recent years, many types of liquid crystal display element control integrated circuits have already been developed and commercially available for use in controlling dot-matrix type liquid crystal display elements, which are often used in large-sized liquid crystal displays, but none of them are perfect in all respects. Currently, it is not always possible to obtain products that are suitable for the intended use.

Among them, there is one that is particularly useful for displaying kanji characters, etc., and there is an alternating current signal that instructs the cycle of polarity reversal of the applied voltage,
A signal indicating the frame scanning period by the scanning electrode group is output as a common signal. Conventionally, it has been preferable that the applied voltage polarity not be reversed during one frame scanning period, that is, the frame scanning cycle by the scanning electrode group, but that the applied voltage polarity be reversed at the same time as the start of the next frame scanning. It was common. This integrated circuit for controlling a liquid crystal display element can be used in combination with an integrated circuit for driving a liquid crystal display element that is designed in advance to be easily interfaced with this integrated circuit for controlling a liquid crystal display element to cause a liquid crystal display element to display a desired display. Of course.

However, when using a control integrated circuit in which the frequency of the alternating signal is relatively low, the threshold voltage of the liquid crystal display element depends on the driving frequency, so the display with a low spatial frequency is dark, and the display with a low spatial frequency is dark. There was a problem in that the display in areas where the height changes relatively quickly becomes thinner and uneven, resulting in an unsightly appearance. On the other hand, Japanese Patent Application Laid-Open No. 2003-100002 discloses that the cycle of the alternating current signal that inverts the polarity of the voltage applied to the electrodes is made shorter than the frame scanning cycle, and the polarity of the applied voltage is inverted one or more times in the middle of one frame scanning cycle. This proposal is proposed in Publication No. 1983-50119, but in this proposal, when an integrated circuit for controlling a liquid crystal display element outputs a signal common to a signal indicating the alternating current cycle and a signal indicating the frame scanning cycle. No special consideration was given to this.

[Problem that the invention seeks to solve]

The present invention uses an integrated circuit for controlling a liquid crystal display element which outputs an alternating current signal and a frame scanning period signal for inverting the applied voltage polarity every frame scanning period, which has been generally used as described above. An object of the present invention is to provide a liquid crystal display device in which display unevenness does not occur even when the display is uneven.

[Means for solving problems]

In order to solve the above problems, in the present invention, a signal used in common for a signal indicating a frame scanning period and a signal indicating an alternating current conversion period is used as a scan start command signal for each frame to the scanning electrode group and an alternating current signal for each frame. means for separating the alternating current signal into an alternating current signal, and a signal obtained by arbitrarily dividing a strobe signal outputted as many times as the number of scanning electrodes per frame scanning period;
means for creating an alternating current signal having a shorter period than the alternating signal by passing it through an exclusive OR gate;
The scanning start command signal and the short-cycle alternating current signal are used to drive the liquid crystal display element.

[Effect]

With the above configuration, the polarity of the voltage applied to the electrodes is reversed at least once during the scanning period of a certain frame. The reason why display unevenness occurs is that the threshold voltage of a liquid crystal display element depends on the driving frequency. This is because the display becomes thinner in areas where the display changes relatively quickly, so by increasing the number of times the applied voltage polarity is reversed, the polarity of the voltage applied to the electrodes can continue for a long period of time (one frame scanning period). There are fewer parts that are kept the same, and therefore display unevenness is reduced.

However, if the frequency of the alternating current signal is increased by an integer multiple, for example, twice, display irregularities will always appear along the horizontal line in the vertical center of the display screen, even if the degree of shading is small. Easy to notice. Further, for example, if the frequency is set to a frequency that is different by 1 from 2 times instead of just 2 times, the voltage polarity inversion position will move one scanning electrode at a time in each frame, which is also easy to notice. The voltage polarity is reversed at a position quite far away on the display screen for each frame.
It is desirable that the position be constantly varied. To do this, as mentioned above, the strobe signal output per frame period is divided as many times as the number of scanning electrodes.
This frequency-divided signal and the alternating current signal output from the display device control integrated circuit are put into one exclusive OR gate, and the original alternating signal is converted into the strobe signal in the middle of the original period. is inverted one or more times using a frequency-divided signal (1-
This can be easily carried out by creating a short-cycle alternating current signal (0 or 0-1).

〔Example〕

FIG. 1 is a block diagram showing the main circuit parts of an embodiment of the present invention, in which 1 is a D flip-flop, 2 is an exclusive OR gate,
3 is a counter, 4 is an inverter, 5 is a signal (FRM signal) that serves as both a frame scanning periodic signal and an alternating current periodic signal,
6 is a frame scanning start command signal (FLM signal) separated from the FRM signal, and 7 is an alternating current signal (M
' double signal, 8 is a strobe signal (STB), and 9 is a clock signal (same as the strobe signal, but used as the clock signal CLI in the display element drive circuit). In this embodiment, the duty cycle is 100 and the scanning voltage is 100), the frame scanning frequency (therefore, the FL
M signal) was set at 35 Hz. Therefore, the frequency of 5TB8 is 3.5kHz. The original AC signal M separated from the FRM signal 5 commands polarity reversal every 1/35 seconds.

In this embodiment, the shortened AC signal is approximately 1/20
Commands polarity reversal every 0 seconds. Note that the part within the broken line outline in FIG. 1 is a means for separating the FRM signal into an M signal and an FLM signal, and the other parts are means for creating an alternating current signal M° from an alternating current signal M with a short period.

Moreover, FIG. 2 is a timing chart of each signal. Since the FRM signal of the first D flip-flop and the inverter rises earlier than the FLM signal required by the drive circuit by 5TB1 pulses, the phases of the first D flip-flop and inverter are adjusted to suitably match the FRM signal as the FLM signal.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to obtain a dot matrix type liquid crystal display device that provides an easy-to-see and pleasant display with less display unevenness by adding only a small number of circuits.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the main parts of a circuit according to an embodiment of the present invention, and FIG. 2 is a timing chart of each signal in the device of the present invention.

Claims (1)

[Claims] 1. A dot matrix type liquid crystal display element having a large number of scanning electrode groups and a large number of display electrode groups, each perpendicular to each other, is controlled by an alternating current signal indicating the period for reversing the polarity of the applied voltage and a frame scanning period by the scanning electrode group. In a liquid crystal display device, the common signal is controlled by an integrated circuit for controlling a liquid crystal display element that outputs a signal shown as a common signal, and the common signal is separated into a scan start command signal for each frame to a group of scan electrodes and an alternating current signal. the alternating current signal, and a signal obtained by arbitrarily dividing the strobe signal output by the number of scanning electrodes per frame period, through an exclusive OR gate to make the cycle shorter than the alternating signal. A liquid crystal display device, further comprising: means for creating an alternating current signal, and the liquid crystal display element is driven using the scan start command signal and the short-cycle alternating signal.