JPH0561430A - Liquid crystal driving circuit - Google Patents

Abstract

PURPOSE:To prevent the DC offset of a driving signal to a liquid crystal panel from being generated. CONSTITUTION:The liquid crystal driving circuit consists of a brightness adjusting circuit 14 for an input video signal (a), a multiplex driver 18 which generates the inverted signal of the brightness-adjusted video signal (b) and puts this inverted signal and uninverted signal together to generate a symmetrical driving signal, and the liquid crystal panel 22. The DC level of the video signal (a) inputted to a DC clip means and a variable slice circuit provided to the brightness adjusting circuit 14 is adjusted to adjust the brightness level of the input video signal (a). Consequently, the inverted signal and uninverted signal have peaks symmetrically about the intermediate potential of a voltage for liquid crystal driving, so the waveform of the uninverted signal is not distorted as a result of the black level adjustment of the liquid crystal panel. Therefore, the DC offset is never generated as a result of the black level adjustment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal drive circuit suitable for application to a video display system using a liquid crystal display element as a two-dimensional display element.

[0002]

2. Description of the Related Art A video display system using a liquid crystal display device as a two-dimensional display device is currently applied to various fields such as office automation equipment and portable small televisions. A liquid crystal drive circuit used in such an image display system is shown in FIG.
The one shown in Fig. 1 is known.

In the liquid crystal drive circuit 10 shown in FIG. 11,
A desired video signal a (FIG. 12A) is supplied to the terminal 12, and the driving signal c as shown in FIG. 12B is formed by supplying the desired video signal a (FIG. 12A) to the multiplex driver 18. Is applied to the two-dimensional liquid crystal panel (LCD panel) 22, so that an image corresponding to the input video signal a is displayed. Reference numeral 20 is a brightness level adjusting resistor, and its amplitude value is changed by adjusting the resistor.

Here, the input video signal a itself is not applied to the liquid crystal panel 22 to drive it, but a drive signal (AC signal) in which an inverted signal and a non-inverted signal of the input video signal a are symmetrically arranged. The reason why the liquid crystal panel 22 is driven under the above condition is that if a DC level signal is continuously applied to the liquid crystal panel 22, image sticking of the liquid crystal may occur and the liquid crystal panel 22 may be damaged (burned). Because.

Therefore, the multiplex driver 18
In FIG. 12B, a signal (non-inverted signal) having the same polarity as the input video signal a (non-inverted signal) and its inverted signal are obtained and combined so as to be symmetrical for each horizontal line, thereby eliminating the DC offset. The drive signal c as shown in FIG.

In FIG. 12B, V is an applied voltage, and V = V1-V0. Here, V1 is the maximum applied voltage, which is approximately equal to the power supply voltage Vcc. V0 is the minimum applied voltage, which is usually a potential near the ground potential, and the minimum applied voltage V0 is determined by adjusting the amplitude d of the drive signal c, and the black level of the liquid crystal (the cutoff level in the picture tube) is determined by this. Is set. Therefore, this minimum applied voltage V0 is semi-fixed. Vp is an intermediate voltage level (= 1/2 V) of the applied voltage V, and the drive signal c is formed so as to have positive / negative symmetry with reference to this intermediate voltage Vp. Then, in this state, the brightness is adjusted by adjusting the amplitude level d (FIG. 12C).
reference).

[0007]

By the way, the above-mentioned method of determining the intermediate potential Vp is performed by applying a drive signal as a test signal, which is symmetrical with respect to the potential applied to the common electrode (not shown) of the liquid crystal panel 22. A potential that does not cause flicker is applied as the intermediate potential Vp.
Since the intermediate potential Vp depends on the characteristics of the liquid crystal panel 22, it is not always 1 / 2V as described above.

When the intermediate potential Vp deviates from 1/2 V, for example, as shown in FIG. 13, when the intermediate potential Vp deviates by Δ toward the minimum potential V0, the black level of the liquid crystal panel 22 is adjusted. When the amplitude of the drive signal c is increased and the amplitude level is adjusted from d to d ', the signal (non-inverted signal) whose DC level is shifted by Δ is clipped by the minimum potential V0. May occur.

Therefore, the inverted signal and the non-inverted signal do not have symmetrical waveforms, and this asymmetrical waveform is applied to the liquid crystal panel 22 as a drive signal. When the DC voltage for this Δ is constantly applied between the common electrode and the drive electrode of the liquid crystal panel 22, the DC offset causes the above-described burn-in, which may cause the liquid crystal panel 22 to burn out or endure use. It will be gone.

Therefore, the present invention solves such a conventional problem, and proposes a liquid crystal drive circuit 10 in which the drive signal is not distorted even by adjusting the black level and DC offset is prevented. is there.

[0011]

In order to solve the above-mentioned problems, according to the present invention, a luminance adjusting circuit for an input video signal and an inverted signal thereof are formed from the luminance-adjusted video signal, and the inverted signal is not generated. The brightness adjustment circuit is composed of a multiplex driver that forms a symmetrical drive signal by combining the inverted signal and a liquid crystal panel.
C clipping means or a variable slice circuit is used, and the luminance level of the input video signal is adjusted by adjusting the DC level or the slice level of the video signal input to this clipping means. It is characterized by.

[0012]

In the embodiment shown in FIG. 1, the input video signal a
Is supplied to the brightness adjusting circuit 14. As shown in FIG. 2, the luminance adjusting circuit 14 clips the video signal whose DC level is adjusted at a predetermined level by the clipping circuit 3.
0, the amplitude level itself of the video signal a is adjusted in the order of A, B, and C in FIG.

The brightness-adjusted video signal a is supplied to the multiplex driver 18, an inverted signal and a non-inverted signal of the video signal a are formed, and both are combined to generate a drive signal c as shown in FIG. 3C. Is formed. And
In the state of the AC drive signal c, the amplitude value d has the variable resistor 20.
To adjust the black level.

By adjusting the brightness level itself of the input video signal a and then forming the positive and negative symmetrical drive signal c, the waveform of the video signal a itself is not distorted by the brightness adjustment, so that the black level is adjusted. Therefore, even if the amplitude value is adjusted, the DC offset does not occur, and the liquid crystal itself does not burn.

Instead of the clip circuit 30, a variable slice circuit 42 as shown in FIG. 8 may be used.

[0016]

Next, a case where an example of the liquid crystal drive circuit according to the present invention is applied to the above-mentioned video signal display device,
A detailed description will be given with reference to the drawings.

FIG. 1 shows an example of a liquid crystal drive circuit 10 according to the present invention, in which a video signal a is applied to a terminal 12.
(FIG. 3A) is supplied, and this is supplied to the brightness adjusting circuit 14 to adjust the brightness level (FIG. 3B). 16
Is a variable resistor for adjustment therefor.

The brightness-adjusted video signal b is supplied to the multiplex driver 18 to form a drive signal c as shown in FIG. 3C.

That is, an inverted signal and a non-inverted signal are formed from the video signal b, and these are combined to form a drive signal c which is an AC signal as shown in FIG. 3C. Then, the black level of the liquid crystal panel 22 is adjusted as desired by the adjusting variable resistor 20 provided in the multiplex driver 18. After adjusting the black level, the variable resistor 20 is semi-fixed.

The drive signal c whose black level has been adjusted is supplied to the corresponding electrode of the liquid crystal panel 22 and driven to display a predetermined image.

The above-mentioned brightness adjusting circuit 14 may have the structure shown in FIG. The DC level of the video signal a itself, which has been amplified by the video amplifier 26, is adjusted by adjusting the DC voltage supplied to the video signal a in the combiner 28. The video signal a whose DC level has been adjusted is further clipped by the black level clipping circuit 3
It is supplied to 0 and is clipped by a predetermined black level (fixed in this example).

Therefore, the video signal a (a1) whose DC level is adjusted and the video signal b after being clipped
The relationship with is as shown in FIG. A in the figure is bright, and when it becomes dark, the amplitude level itself of the video signal b is adjusted to be small as in B and C in the figure. As a result, when the brightness is bright, the drive signal c as shown in FIG. 5 is obtained, and as the brightness is made darker, the drive signal c changes as shown in FIG. 6 or 7.

Since the amplitude level of the video signal a itself is adjusted and clipped to obtain the video signal b after the brightness adjustment, the peak values x1 and x2 of the inverted signal and the non-inverted signal are symmetrical with respect to the intermediate potential Vp. Therefore, even if the variable resistor 20 is used to adjust the amplitude value d to adjust the black level of the liquid crystal panel 22, the non-inverted signal is clipped to the minimum potential V0 and its waveform is distorted. There is no such thing. That is, DC offset does not occur due to the black level adjustment.

Since there is no DC offset, even if the drive signal c thus formed is applied to the liquid crystal panel 22, the liquid crystal will not be burned in, burning will not occur, and the liquid crystal panel will be burned. There is no fear that 22 will become unusable.

FIG. 8 shows another example of the brightness adjusting circuit 14.
In this example, the variable slice circuit 42 is used, and the video signal a supplied to the terminal 12 is clamped to a predetermined level by the clamp circuit 40 (see FIG. 9). Let the video signal after clamping be e. The video signal e is supplied to the variable slice circuit 42. A variable resistor 16 for brightness adjustment is used as an element for adjusting the slice level.

Assuming that the slice level is Si, when the slice level Si is a level S1 larger than the clamp level CL as shown in FIG. 9, the video signal e is sliced at the level CL as shown in FIG. f1 is output. On the other hand, the slice level Si
Is a level S2 smaller than the clamp level CL, the video signal e is output as it is without being sliced. The output video signal at that time is defined as f2.

The sliced video signal f (f1, f
2) If the brightness is adjusted as it is, the pedestal level changes and the black level cannot be reproduced. Therefore, in order to set the slice level to the black level, the video signal f is supplied to the differential amplifier 44 together with the slice level Si. In this way, as shown in FIG. 10, the output video signals b (b1, b2), which are offset by the levels V1 and V2 in FIG. 9 and whose slice level is always the pedestal level, are obtained.

Therefore, when the brightness is adjusted to be bright as shown in FIG. 10, only the DC level changes with the waveform of the input video signal as it is. When the brightness is adjusted to be dark, the video signal waveform operates so as to sneak into the black level.

The above-described brightness adjusting circuit 14 is an example, and any means can be used as long as it can adjust the amplitude level of the video signal a, and various modifications can be made.

[0030]

As described above, in the liquid crystal drive circuit according to the present invention, the DC clip means and the slice circuit provided in the brightness adjusting circuit to which the input video signal is supplied are used to adjust the DC level of the video signal. The DC level is clipped or sliced.

According to this, since the peak values of the inversion signal and the non-inversion signal are symmetrically positioned with respect to the intermediate potential of the liquid crystal panel driving voltage, the non-inversion signal is adjusted by adjusting the amplitude of the black level of the liquid crystal panel. The waveform of is not distorted. Therefore, DC offset does not occur due to the black level adjustment.

Since there is no DC offset, it is possible to prevent the liquid crystal from being burned in or burned out, and the burnout does not render the liquid crystal panel unusable or shorten its life.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example of a liquid crystal drive circuit according to the present invention.

FIG. 2 is a system diagram showing an example of a brightness adjustment circuit.

FIG. 3 is a waveform diagram for explaining the operation of the liquid crystal drive circuit.

FIG. 4 is a waveform diagram for explaining an operation of brightness adjustment.

FIG. 5 is a waveform diagram for explaining an operation of brightness adjustment.

FIG. 6 is a waveform diagram for explaining an operation of brightness adjustment.

FIG. 7 is a waveform diagram for explaining an operation of brightness adjustment.

FIG. 8 is a system diagram showing another example of the brightness adjustment circuit.

FIG. 9 is a waveform diagram for explaining an operation of brightness adjustment.

FIG. 10 is a waveform diagram for explaining an operation of brightness adjustment.

FIG. 11 is a waveform diagram showing an example of a conventional liquid crystal drive circuit.

FIG. 12 is a waveform diagram for explaining an operation of brightness adjustment.

FIG. 13 is an explanatory diagram of amplitude adjustment.

[Explanation of symbols]

 10 liquid crystal drive circuit 12 input terminal 14 brightness adjustment circuit 16 brightness adjustment variable resistor 18 multiplex driver 20 amplitude adjustment variable resistor 22 liquid crystal panel 30 black level clip circuit 42 variable slice circuit 44 differential amplifier

Claims (2)

[Claims] 1. A brightness adjusting circuit for an input video signal, and a multiplex for forming a symmetric drive signal by forming an inverted signal of the brightness adjusted video signal and synthesizing the inverted signal and a non-inverted signal. The brightness adjusting circuit is composed of a driver and a liquid crystal panel, and the brightness adjusting circuit has a DC clipping unit. By clipping the DC level of the video signal input to the clipping unit, the brightness level of the input video signal is adjusted. Liquid crystal drive circuit characterized by what has been done. 2. The brightness adjusting circuit has a variable slice circuit, and the brightness level of the input video signal is adjusted by adjusting the slice level with respect to the DC level of the video signal input to the variable slice circuit. The liquid crystal drive circuit according to claim 1, which is made.