JPH04260092A - Video signal processing circuit for liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve the gradation reproducibility by correcting the linearity of the electrooptic characteristics of liquid crystal and a gamma characteristic for a cathode-ray tube. CONSTITUTION:Input analog video signal are converted by an A/D converter circuits 6-8 into digital video signals, which are outputted to video signal correcting ROMs 9-11. In the ROMs 9-11, the addresses and stored data are related so as to correct the nonlinearity of the electrooptic characteristic of the liquid crystal and the gamma characteristic for the cathode-ray tube. Therefore, when the digital video signals are inputted to the address terminals of the ROMs 9-11, corrected digital signals are obtained at their output terminals. Those are converted by D/A converter circuits 12-14 into analog video signals, which are supplied to a liquid crystal panel.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal processing circuit for a liquid crystal display device.

0002

2. Description of the Related Art Conventionally, as a technique in this kind of field, for example, "Journal of Television Society, Vol. 42 No.
1, P. 23-P. 29 (1988)" is known. FIG. 5 is a block diagram showing the basic configuration of a conventional liquid crystal display device.

In the figure, 1 is a video signal processing circuit to which analog video signals of red (R), green (G), and blue (B) are input; 2 is a timing generation circuit to which a synchronization signal is input; 3;
4 is an X driver that supplies data signals to the liquid crystal panel 5;
is a Y driver that supplies a scanning signal to the liquid crystal panel 5. The timing generation circuit 2 generates control signals for the video signal processing circuit 1, the X driver 3, and the Y driver 4 from the synchronization signal.

[0004] The video signal processing circuit 1 has a function of converting an input analog video signal into a signal that matches the characteristics specific to the liquid crystal. The X driver 3 receives the video signal converted by the video signal processing circuit 1 and the control signal from the timing generation circuit 2, and supplies the liquid crystal panel 5 with a data signal that is a video signal voltage.

A control signal is input from the timing generation circuit 2 to the Y driver 4, and a scanning signal is supplied to the liquid crystal panel 5. FIG. 6 is a block diagram showing a video signal processing circuit in a conventional liquid crystal display device. Furthermore, Figure 7 shows the electro-optical characteristics of a liquid crystal cell, in which light is transmitted when a voltage equal to or higher than the threshold voltage VTH is applied, and the light transmittance is saturated at a voltage equal to or higher than the saturation voltage VSAT. .

In FIG. 6, 26, 27, and 28 are amplifiers that amplify R, G, and B video signals, respectively, and perform contrast adjustment so that the video output amplitude corresponds to VSAT-VTH in FIG. Phase division circuit 29, 30, 3
1 generates video signals of positive polarity and negative polarity, and output switching circuits 32, 33, and 34 form AC video signals whose polarities are inverted for each field. This is done in order to reverse the polarity of the applied voltage that drives the liquid crystal at regular intervals, thereby preventing a decrease in the life of the liquid crystal.

The output switching circuits 32, 33, and 34 are controlled by a flip-flop 35 that outputs a control signal whose polarity is inverted (every field) at the cycle of the vertical synchronizing signal. Brightness is set so that the lower end level of the video amplitude matches the threshold voltage VTH in FIG. Therefore, the relationship between the input video signal to the video signal processing circuit 1 and the output video signal (positive polarity only) is as shown in FIG.

[0008]

[Problems to be Solved by the Invention] However, in the video signal correction circuit of the liquid crystal display device having the above configuration,
In the electro-optical characteristics of the liquid crystal panel shown in the figure, the relative transmittance with respect to the applied voltage has non-linearity on the low transmittance side and the high transmittance side, so the transmittance of the liquid crystal panel obtained for the input video signal is as shown in the figure. As shown in 9, the characteristics directly reflect the nonlinearity described above. That is, there was a problem in that the gradation reproducibility on the low transmittance side and the high transmittance side deteriorated.

[0009] Furthermore, since the standardized video signal is designed to correct the gamma characteristic (square law) of the cathode ray tube, this gamma characteristic correction characteristic is reproduced on the liquid crystal display, resulting in poor gradation reproducibility. There was a problem in that the value decreased. The present invention solves the above-mentioned conventional problems by correcting the amplitude of the video signal to match the electro-optical characteristics of the liquid crystal, or by restoring the γ characteristics corrected for cathode ray tubes, and by adjusting the amplitude to match the characteristics of the liquid crystal. It is an object of the present invention to provide a liquid crystal display device capable of high-quality display with excellent gradation reproducibility by re-correcting as described above.

0010

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a video signal processing circuit for a liquid crystal display device that converts an input video signal into a signal that matches the characteristics unique to the liquid crystal. A video signal correction ROM whose relationship between and stored data corresponds to the desired video signal correction characteristics is provided, a digital video signal is input to the address input terminal of the ROM, and the digital video signal whose characteristics are corrected is output from the output terminal of the ROM. This outputs the following.

[0011]

[Operation] According to the present invention, since the video signal processing circuit of the liquid crystal display device is configured as described above, the video signal correction ROM provided in the video signal processing circuit
As a result, correction is made to match the electro-optic characteristics of the liquid crystal, return the γ characteristics corrected for cathode ray tubes, and make corrections that match the electro-optic characteristics of the liquid crystal. As a result, the output of the video signal processing circuit provides the liquid crystal display with excellent gradation reproducibility.

0012

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing the configuration of a video signal processing circuit according to the present invention. In the figure, 6, 7,
8 is an A/D converter circuit, 9, 10, 11 is a video signal correction ROM, 12, 13, 14 is a D/A converter circuit, 15, 16, 17 is an amplifier, 18, 19, 20 is a phase division circuit, 21 , 22, 23 are output switching circuits, and 24 is a flip-flop circuit.

[0013] R, G, B analog video signals are A/D
The signals are input to converter circuits 6, 7, and 8 and converted into digital signals. Digital signal is video signal correction ROM9,1
It is input to address terminals 0 and 11. Video signal correction R
OM9, 10, and 11 store data in which, for example, the relationship between the address input code and the code stored at the address is such that the electro-optical characteristics of the liquid crystal are corrected as shown in FIG. . That is, the relative transmittance shown in FIG. 7 corresponds to the address input code, and the voltage from VTH to VSAT shown in FIG. 7 corresponds to the stored code.

The outputs of the video signal correction ROMs 9, 10, 11 are input to D/A converter circuits 12, 13, 14 and converted into analog signals. This analog signal is transmitted to amplifiers 15, 16, 17, phase division circuits 18, 19, 20
, are sequentially input to the output switching circuits 21, 22, 23,
These operations are similar to those of the amplifiers 26 and 2 described in the conventional example in FIG.
7, 28, phase division circuits 29, 30, 31, and output switching circuits 32, 33, 34, so explanations will be omitted.

As explained above, since the video signal processing circuit has the video signal correction circuit, the relationship between the input video signal to the video signal processing circuit of the present invention and the output video signal (positive polarity only) is as shown in FIG. As a result, the relationship between the input video signal and the relative transmittance of the liquid crystal panel becomes as shown in FIG. 4, and display characteristics with excellent linearity of gradation characteristics are obtained.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and various modifications can be made based on the spirit of the present invention, and these are not excluded from the scope of the present invention. For example, in the above explanation, an example was described in which only the electro-optical characteristics of the liquid crystal panel were corrected, but it is also possible to restore the correction of the gamma characteristics of the cathode ray tube included in the standardized video signal, or to obtain arbitrary gradation characteristics. The thing is that video signal correction RO
It is clear that this can be easily achieved by changing the data of M.

[0017] Furthermore, if the input signal is a digital signal,
Video signal correction ROM without passing through the A/D converter circuit
It is also obvious that it may be input directly to the address terminal of the address terminal.

[0018]

As described in detail above, according to the present invention, in the video signal processing circuit of a liquid crystal display device that converts an input video signal into a signal that matches the characteristics unique to the liquid crystal, Provide a video signal correction ROM whose relationship with the desired video signal correction characteristics corresponds to the desired video signal correction characteristics, and
Since the configuration is such that a digital video signal is input to the address input terminal of M, and a digital video signal with corrected characteristics is output from the output terminal of the ROM, the video signal correction ROM
A liquid crystal display device with excellent gradation reproducibility by storing data for correcting the electro-optical characteristics of the liquid crystal, restoring the γ characteristics corrected for cathode ray tubes, or obtaining arbitrary gradation characteristics. can be realized, and also arbitrary gradation characteristics can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a video signal processing circuit in an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing the relationship between addresses and stored data of a video signal correction ROM in an embodiment of the present invention.

FIG. 3 is an input/output characteristic diagram of the video signal processing circuit in the embodiment of the present invention.

FIG. 4 is a characteristic diagram showing the relative transmittance of a liquid crystal with respect to an input video signal in an embodiment of the present invention.

FIG. 5 is a block diagram showing the basic configuration of a conventional liquid crystal display device.

FIG. 6 is a block diagram showing the configuration of a conventional video signal processing circuit.

FIG. 7 is an electro-optical characteristic diagram of liquid crystal.

FIG. 8 is an input/output characteristic diagram of a conventional video signal processing circuit.

FIG. 9 is a characteristic diagram showing the relative transmittance of liquid crystal to an input video signal in a conventional liquid crystal display device.

[Explanation of symbols]

6,7 A/D converter circuit 9-11
Video signal correction ROM12-14D
/A converter 15-17 Amplifier 18-20 Phase division circuit 21-23 Output switching circuit

Claims (4)

[Claims] Claim 1: In a video signal processing circuit of a liquid crystal display device that converts an input video signal into a signal that matches the characteristics unique to the liquid crystal, a video signal whose relationship between addresses and stored data corresponds to desired video signal correction characteristics is used. 1. A video signal processing circuit for a liquid crystal display device, comprising a signal correction ROM, inputting a digital video signal to an address input terminal of the ROM, and outputting a digital video signal with corrected characteristics from an output terminal of the ROM. 2. A circuit that converts an input analog video signal into a digital video signal and inputs it to a video signal correction ROM, and a circuit that converts the digital video signal output from the ROM into an analog video signal. A video signal processing circuit for a liquid crystal display device according to claim 1. [Claim 3] The non-linearity of the relative transmittance with respect to the applied voltage of the liquid crystal is corrected by making the video signal correction ROM address correspond to the relative transmittance in the electro-optical characteristics of the liquid crystal, and by making the stored data correspond to the applied voltage. A video signal processing circuit for a liquid crystal display device according to claim 1. 4. (a) a circuit that converts an input analog video signal into a digital video signal; (b) the digital video signal is supplied to an address input terminal, and the relationship between the address and the stored data is such that the desired video signal is converted. (c) a video signal correction ROM corresponding to signal correction characteristics; and (c) the video signal correction RO.
a circuit for converting the output digital video signal of M into an analog video signal; (d) a circuit for adjusting the contrast of the analog video signal; and (e) generating positive and negative analog video signals from the output of the circuit. and (f) a circuit that switches and outputs the positive and negative analog video signals at predetermined intervals.