JP2003216119A - Circuit for driving liquid crystal panel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the driving device of a liquid crystal panel for effectively dissolving occurrence of failure such as a vertical stripe over entire gradation of an input video signal. <P>SOLUTION: The driving circuit of a liquid crystal panel, for example, the driving circuit of an active matrix type liquid crystal panel in which a driver using poly crystalline silicon transistors is incorporated is provided with a detecting circuit detecting the level of the input video signal and a precharge signal generating circuit generating a precharge signal having a signal level corresponding to the level of the input video signal which is detected by the detecting circuit. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for a liquid crystal panel, for example, a drive circuit for an active matrix type liquid crystal panel having a built-in driver using a polycrystalline silicon transistor.

[0002]

2. Description of the Related Art FIG. 1 shows an electrical configuration of a liquid crystal projector.

R, G, B input to the liquid crystal projector
The signal is converted into a digital signal by the A / D converter 1 and then sent to the digital signal processing circuit 2 to be subjected to processing such as brightness adjustment, contrast adjustment, gamma correction and the like. R output from the digital signal processing circuit 2,
The G and B signals are time-divided by the sample & hold circuit 3, converted into analog signals by the D / A converter 4, and written in the liquid crystal panel 6. The signal written in the liquid crystal panel 6 is projected on the screen.

The timing generator 5 supplies a clock to the A / D converter 1, the digital signal processing circuit 2, the sample & hold circuit 3 and the D / A converter 4, and also supplies a panel drive pulse to the liquid crystal panel 6. As the liquid crystal panel 6, an active matrix type liquid crystal panel having a built-in driver using a polycrystalline silicon transistor is used.

In order to prevent the liquid crystal from being deteriorated due to an electrochemical reaction due to a direct current component,
As shown in FIG. 2, an alternating current is provided so as to be symmetrical with respect to the center voltage of the video signal. Since the AC-converted video signal applied to the liquid crystal panel 6 suddenly changes from the positive polarity to the negative polarity, the voltage applied to the liquid crystal is insufficiently written, causing a defect such as a vertical stripe in the projected image. In order to solve the occurrence of this problem, conventionally, as shown in FIG.
As shown in, the precharge signal having the same polarity as the alternating video signal is written in the liquid crystal panel 6 in advance.

The precharge signal level is determined according to the liquid crystal panel, and is generally set so that defects such as vertical stripes are not noticeable when the video signal level is in a halftone.

FIG. 2 shows a state in which the input video signal is divided into three gradations from white to black within one horizontal period. In FIG. 2, the precharge signal has a constant value within one horizontal period.

In the conventional liquid crystal projector as described above, when the input video signal level is a level corresponding to a preset precharge signal level, a defect such as a vertical stripe does not occur, but the input video signal level is When the level does not correspond to the precharge signal level set in advance, a slight defect such as a vertical stripe occurs.

That is, the conventional liquid crystal projector has a problem in that it is impossible to effectively eliminate defects such as vertical stripes over all gradations of the input video signal.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid crystal panel drive device capable of effectively eliminating the occurrence of defects such as vertical stripes over all gradations of an input video signal. And

[0011]

According to a first aspect of the present invention, in a drive circuit for an active matrix type liquid crystal panel, a means for controlling a precharge signal level according to an input video signal level is provided. To do.

According to a second aspect of the present invention, in a drive circuit of an active matrix type liquid crystal panel, a detection circuit for detecting an input video signal level, and a precharge signal having a signal level corresponding to the input video signal level detected by the detection circuit. Is provided with a precharge signal generating circuit.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS.

FIG. 3 shows an electrical configuration of the liquid crystal projector according to the embodiment of the present invention. In FIG. 3, the same parts as those in FIG.

In the liquid crystal projector of the embodiment of the present invention, a video signal level detection circuit 7 and a precharge signal generation circuit 8 are added as compared with the liquid crystal projector of FIG.

The video signal level detection circuit 7 is a circuit for detecting the signal level of the digital signal obtained by the digital signal processing circuit 2, and the detected signal level is sent to the precharge signal generation circuit 8.

The precharge signal generation circuit 8 generates an optimum level precharge signal based on the signal level detected by the video signal level detection circuit 7.
The precharge signal generated by the precharge signal generation circuit 8 is sent to the liquid crystal panel 6.

The timing generator 5 controls the alternating video signal and the precharge signal applied to the liquid crystal panel 6 to have the same polarity. .

FIG. 4 shows a video signal and a precharge signal which are supplied to the liquid crystal panel 6 and are made into an alternating current.

FIG. 4 shows a state in which the input video signal is divided into three gradations from white to black within one horizontal period.

Since the precharge signal generation circuit 8 generates a precharge signal having a level according to the signal level of the input video signal, the signal level of the precharge signal is also divided into three stages according to the video signal.

Therefore, since the optimum precharge signal is generated according to the input level of the input video signal, it becomes possible to eliminate the problems such as vertical stripes over all the gradations of the input video signal.

[0023]

According to the present invention, it becomes possible to effectively eliminate the occurrence of defects such as vertical stripes over all gradations of an input video signal.

[Brief description of drawings]

FIG. 1 is a block diagram showing a conventional example.

FIG. 2 is a timing chart showing an alternating video signal and a precharge signal supplied to a liquid crystal panel in the conventional example of FIG.

FIG. 3 is a block diagram showing an embodiment of the present invention.

FIG. 4 is a timing chart showing an AC-converted video signal and a precharge signal supplied to a liquid crystal panel in the embodiment of the invention shown in FIG.

[Explanation of symbols]

1 A / D converter 2 Digital signal processing circuit 3 Sample and hold circuit 4 D / A converter 5 Timing generator 6 LCD panel 7 Video signal level detection circuit 8 Precharge signal generation circuit

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H093 NC00 NC11 NC52 NC58 ND01                       ND10 ND15                 5C006 AA22 AC26 AF45 BB16 BC12                       EC11 FA22                 5C080 AA10 BB05 CC03 DD05 EE28                       FF11 JJ02 JJ04 KK43

Claims (2)

[Claims] 1. A drive circuit for an active matrix type liquid crystal panel, comprising a means for controlling a precharge signal level according to an input video signal level. 2. A drive circuit of an active matrix type liquid crystal panel, a detection circuit for detecting an input video signal level, and a precharge for generating a precharge signal having a signal level according to the input video signal level detected by the detection circuit. A drive circuit for a liquid crystal panel, comprising: a signal generation circuit.