JPS63274932A - Liquid crystal driving circuit - Google Patents

Abstract

PURPOSE:To improve the display quality by driving a liquid crystal by an AC converting signal of exclusive OR of a signal which has brought a line sequential timing signal to a frequency division, and a signal which has brought to a timing signal of a frame to a frequency division. CONSTITUTION:A liquid crystal is driven by an AC converting signal M' outputted from exclusive OR 3 of both frequency dividing signals of an A frequency dividing counter 1 of a line sequential timing signal CL1, and a B frequency dividing counter 2 of a timing signal FLM of a frame. In such a way, a polarity inversion of a driving signal at the time of switching of the frame can be eliminated, and by eliminating an abnormal state of variable density of a first common line, the display quality can be raised.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention particularly relates to a liquid crystal drive circuit using high duty time division driving.

[Summary of the invention]

The present invention drives a liquid crystal using an AC signal that is the exclusive OR of a signal obtained by dividing a line-sequential timing signal and a signal obtained by dividing a frame timing signal, in a liquid crystal driving method using time division driving. This is intended to improve display quality.

[Conventional technology]

When driving a liquid crystal, if a direct current component remains in the drive signal, the characteristics of the liquid crystal deteriorate, so the liquid crystal must be driven with an alternating current signal. Generally, when the duty is relatively low (1/64 duty or less), the polarity of the drive signal is reversed every frame to convert it to AC, but with this method, the deterioration in display quality becomes more noticeable as the duty increases. . This is because the difference in frequency components of the drive waveform due to the difference in display patterns becomes significant, which appears as display unevenness on the liquid crystal screen.

Therefore, in the case of high-duty time-division driving, measures have been taken to reduce the difference in frequency components of drive waveforms due to differences in display patterns by combing the frequency of alternating current as much as possible. Specifically, the exclusive OR of a signal obtained by frequency-dividing the line-sequential timing signal and a signal that is inverted for each frame is used as the alternating current signal. The frequency division ratio is selected to reduce display unevenness while looking at the actual display on the liquid crystal panel. Since a signal obtained by simply frequency-dividing a line-sequential timing signal generally has a residual DC component, the exclusive OR with a signal that is inverted every frame is used as an AC signal. It is known that display unevenness can be considerably reduced by driving the liquid crystal with such a signal.

[Problem that the invention seeks to solve]

However, the conventional AC conversion method has the following drawbacks. That is, because of the circuit configuration that performs an exclusive OR with a signal whose polarity is inverted for each frame, there is a high probability that the inversion of the polarity of the alternating current signal will coincide with the frame switching time.

For example, when the duty is 1/200 and the frequency division ratio is 35, the AC signal is as shown in FIG. 2, and it is clear that the polarity is often reversed when switching frames.

Now, at the time of this polarity reversal, the drive signal changes differently than when the polarity is normally constant, so that the effective value of the voltage actually applied to the liquid crystal is disturbed. For this reason, the display shading of the common line selected immediately after the polarity inversion is different from that of other common lines.

This disturbance in the effective value of the applied voltage is affected by many factors such as the ability of the eIC, the characteristics of the liquid crystal, and the resistance value of the transparent electrode of the panel, and cannot be completely eliminated.

Therefore, in the conventional alternating current method, a phenomenon occurs in which the display shading of the first common line immediately after frame switching is different from that of the others. This is particularly important when moving the display screen up and down.
When driving separately, the common line in the center of the screen is 1
Only the books had different shading, which was very noticeable depending on the display pattern and degraded the display quality.

(Means for solving the problem) In order to solve the above problem, we improved the method of exchange,
The polarity reversal is prevented from concentrating at the time of frame switching, and the density abnormality of the first common line is removed. In other words, in the past, in order to convert the line-sequential frequency-divided timing signal into AC, an exclusive OR with a signal whose polarity is inverted for each frame was performed, but in the method according to the present invention, the timing signal of the frame is Perform exclusive OR with the frequency-divided signal. The frequency division ratio is determined based on the relationship with the frequency division ratio of the line-sequential timing signal, so that no DC component remains in the drive signal.
In addition, settings are made so that polarity reversals do not concentrate when switching frames. For example, if the duty is 1/200 and the division ratio of the line sequential timing signal is 35, the third
As shown in the figure, the frequency division ratio of the frame timing signal is set to 7.
shall be.

Generally, when the duty is 1/D, the frequency division ratio of the line sequential timing signal is A, and the frequency division ratio of the frame timing signal is 8, if the least common multiple of D and A is C, then B-
If C/D is used, no DC component remains in the drive signal, and polarity reversal does not occur when switching frames.

[Effect]

As shown in Figure 3, by the above-mentioned alternating current method,
Since the polarity reversal is no longer concentrated at the time of frame switching, the shading abnormality of the first common line is completely eliminated.

〔Example〕

An embodiment of the present invention will be described below.

FIG. 1 shows a block diagram of a circuit system for realizing the AC conversion method of the present invention. Line sequential timing signal @(C
LI) A frequency division counter 1. It consists of a frame timing signal (FLM) B frequency division counter 2 and an exclusive OR 3. An alternating current signal M' is output.

FIG. 4 shows a specific circuit example. Frequency division ratio A of CLl,
The frequency division ratio B of the FLM can be selected by switching switches SW1 to SW16.

〔Effect of the invention〕

As explained above, in the present invention, the liquid crystal is driven using an AC signal that is the exclusive OR of a signal obtained by dividing a line-sequential timing signal and a signal obtained by dividing a frame timing signal. Therefore, it is possible to eliminate the polarity reversal of the drive signal at the time of frame switching, and it is possible to eliminate the shading abnormality of the first common line and improve the display quality.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an AC signal generation circuit of the present invention;
FIG. 2 is a diagram showing the timing of the AC conversion signal in the conventional example, FIG. 3 is a diagram showing the timing of the AC conversion signal in the embodiment of the present invention, and FIG. 4 is a diagram showing the AC conversion signal generation circuit in the embodiment of the present invention. It is a circuit diagram. CLI...Line sequential timing signal FLY...Frame timing signal M...Signal M' whose polarity is inverted every frame...AC conversion signal C10...Signal CL4 obtained by dividing CLl by 35.・・F
LM divided by 7 signal 1...A frequency division counter 2...B frequency division counter 3.10...Exclusive OR gate 4.5, 7.8...Programmable counter 6.9.
・・D type flip 70 two boots 〇-

Claims (1)

[Claims] In a liquid crystal drive circuit using time-division driving, a liquid crystal drive that drives the liquid crystal using an AC signal that is the exclusive OR of a signal obtained by dividing a line-sequential timing signal and a signal obtained by dividing a frame timing signal. circuit.