JPH10123485A - Liquid crystal display - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To realize a liquid crystal monitor capable of sufficiently satisfying appropriate image quality, that is, contrast and linearity in a wide temperature range. SOLUTION: A correction circuit for correcting an input video signal by compensating a light transmission characteristic of a liquid crystal and a temperature dependency of the light transmission characteristic according to a control signal, and a signal corresponding to the ambient temperature is controlled by the control signal. A temperature detection circuit provided to the correction circuit. The correction circuit includes a gamma signal amplifier circuit for compensating for linearity in the light transmission characteristics of the liquid crystal, a drive adjustment circuit for compensating for contrast characteristics, a cutoff adjustment circuit for compensating for luminance characteristics, and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device in general, and more particularly to a liquid crystal driving device for compensating for the temperature dependence of the luminance and contrast characteristics of a liquid crystal.

[0002]

2. Description of the Related Art In general, in a TFT liquid crystal module, a light transmittance (VT curve) for an input signal does not have a linear characteristic as shown in FIG. 3, and therefore, a driving circuit is required to compensate for the linearity. In the above, each of the RGB signals is subjected to inverse correction of the VT curve and added to the TFT active element.

The VT curve has a temperature characteristic peculiar to the TFT and shifts in the opposite directions at high and low temperatures (see FIG. 2). When this phenomenon is monitored while maintaining the same contrast while keeping the signal amplitude area constant, blackening occurs at high temperatures,
When the temperature is low, the direction of whitening is lost, and the maximum contrast state cannot be maintained.

Similarly, if this state is monitored with a constant brightness (bright / dark) characteristic, the characteristics of the gamma correction amplifier circuit in the video input signal for correcting the VT curve peculiar to the liquid crystal have no temperature dependency. Therefore, it is impossible to follow the change of the VT curve at the time of high temperature and at the time of low temperature, and as a result, it is not possible to maintain the optimal linearity (linearity).

[0005] As described above, the characteristic of V-
In a video signal correction circuit necessary for visually correcting the T-curve, it has not been possible to keep the optimum contrast and linearity constant regardless of temperature changes.

Conventionally, to solve this problem, TF
In the T-active matrix, a circuit has been proposed in which a common applied voltage as a counter electrode has a temperature characteristic to perform temperature compensation of the VT characteristic. In this method, however, a simple input circuit shown in FIG. Since this is equivalent to shifting the signal axis to the left and right, the movement of the inflection point in the VT characteristic cannot be corrected, and as a result, the optimal linearity characteristic cannot be realized.

[0007]

As described above, in the conventional liquid crystal driving circuit, it is difficult to realize the maximum contrast in a wide temperature range due to the temperature dependence of the V-T curve peculiar to the liquid crystal module.

Further, since the inflection point of the VT curve also has temperature dependence, linearity characteristics cannot be obtained in a wide temperature range. Accordingly, it is an object of the present invention to provide a liquid crystal display device which can obtain good contrast and linearity in a wide temperature range in order to solve the above problems.

[0009]

The liquid crystal driving circuit according to the present invention is a means for solving the problem relating to the temperature dependency of the VT characteristic of the liquid crystal, which is corrected by a temperature compensation function in the liquid crystal driving circuit. It is possible to reproduce an appropriate image.

That is, the liquid crystal drive circuit according to the present invention receives an image signal and a control signal, and compensates for the light transmission characteristic of the liquid crystal and the temperature dependence of the light transmission characteristic according to the control signal, thereby obtaining the input image signal. A correction circuit for correcting a signal, and a temperature detection circuit for detecting an ambient temperature and providing a signal corresponding to the ambient temperature to the correction circuit as the control signal are provided.

Further, the correction circuit of the liquid crystal drive circuit according to the present invention is characterized in that the correction circuit includes a gamma signal amplifier circuit for compensating for the linearity of the light transmission characteristic of the liquid crystal. Further, the correction circuit of the liquid crystal drive circuit according to the present invention includes a drive adjustment circuit for compensating a contrast characteristic of the liquid crystal.

Further, the correction circuit of the liquid crystal driving circuit according to the present invention is characterized in that the correction circuit includes a cutoff adjustment circuit for compensating for the luminance characteristics of the liquid crystal. The cutoff level, drive level and gamma operation level of the liquid crystal transfer signal are changed according to the ambient temperature, and are set so that the optical characteristics of the entire liquid crystal display device can be optimized. That is, visual contrast and linearity can be optimized in a wide temperature range.

[0013]

Embodiments of a liquid crystal display device according to the present invention will be described below with reference to the drawings. FIG. 1 is a circuit block diagram showing one embodiment of the liquid crystal display device of the present invention. The composite video signal input is input to a gamma correction circuit 2 after being triaxially demodulated into RGB signals by a video demodulation circuit 1. The gamma correction circuit 2 amplifies the RGB signal having the standard linearity characteristic, and adjusts the amplification degree by applying inverse correction to the VT curve peculiar to the liquid crystal.

Next, each signal is input to the polarity inversion circuit 3,
It is converted into an AC inversion signal necessary for driving the liquid crystal. Next, a signal amplitude range is set so as to be input to the drive adjustment circuit 4 so as to obtain a necessary contrast. The cut-off adjustment circuit 5 at the next stage determines the DC reproduction rate of the black level and changes the luminance characteristics (brightness adjustment). Each of the above circuits 1 to
At 5, a signal input level required for driving the liquid crystal is set and input to the liquid crystal module 10. A synchronized inverted signal (V-COM) is input to the common counter electrode.

The above configuration is the same as that of the conventional liquid crystal driving external signal circuit. Next, the following processing according to the present invention is performed to compensate for the temperature change of the VT curve specific to the liquid crystal.

A change in the ambient temperature is detected by converting a temperature change into a voltage change in a temperature detection circuit 6 composed of a thermistor or the like. This voltage indicating the temperature is converted by the voltage conversion circuit 7 so that the gamma correction circuit 2, the drive adjustment circuit 4, and the cutoff adjustment circuit 5 fall within the required variable voltage range.
-9 are level-converted.

An actual operation at a high temperature will be described with reference to FIG. FIG. 2A shows the ambient temperature Ta = −30 °.
9 shows TV (transmittance / applied voltage) characteristics of the liquid crystal at C, 25 ° C., and 70 ° C. As can be seen from the graph of FIG. 2A, at a high temperature, the luminance 100% level shifts to the left,
When the maximum contrast is obtained at a normal transfer signal level at normal temperature, that is, in a level range of a normal input signal, when the signal level is low, black is lost and perfect white cannot be reproduced. Therefore, in the case of such a high temperature, the amplification of the cut-off adjustment circuit 5 changes the cut-off level in one direction (left direction in FIG. 2A) while keeping the drive level, that is, the amplitude range constant. Change the degree. This rate of change is determined by the temperature detection circuit 6 and the voltage conversion circuit 9.

The following processing is performed for the rate of change of the VT curve at high temperature, that is, for the change in the slope. From FIG. 2 (b),
When the maximum contrast is obtained in the normal brightness setting, the VT curve has a steep slope due to the temperature characteristics of the cutoff level at a high temperature. Therefore, it is necessary to set the amplification degree of the drive adjustment circuit 4 in one direction, that is, the range of the signal amplitude to set an appropriate contrast.

This processing is performed in the temperature detection circuit 6 and the voltage conversion circuit 8, and by appropriately compensating the rate of change, the loss of white and the loss of black are prevented. Finally, with respect to the movement of the inflection point of the VT curve, the operating point of the gamma correction circuit 2 can be moved in a similar manner to apply temperature compensation. At the time of low temperature shown in FIG. 2 (c), each amplification factor is set so that the above operation works in the opposite direction.

[0020]

As described above, according to the present invention, it is possible to realize a liquid crystal monitor capable of sufficiently satisfying appropriate image quality, that is, contrast and linearity in a wide temperature range. In particular, the effect can be exerted in severe use conditions under temperature conditions, such as in a vehicle or an aircraft.

[Brief description of the drawings]

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

FIG. 2 shows an example of a temperature drift of a VT characteristic in a liquid crystal display device.

FIG. 3 shows an example of a VT characteristic of a liquid crystal display element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Video demodulation circuit 2 ... Gamma correction circuit 3 ... Drive adjustment circuit 4 ... Cutoff adjustment circuit 5 ... Polarity inversion circuit 6 ... Temperature detection circuit 7-9 ... Voltage conversion circuit 10 ... Liquid crystal module

Claims (5)

[Claims] A correction circuit that receives a video signal and a control signal, and corrects the input video signal by compensating a light transmission characteristic of a liquid crystal and a temperature dependency of the light transmission characteristic according to the control signal; A temperature detection circuit that detects an ambient temperature and provides a signal corresponding to the ambient temperature to the correction circuit as the control signal;
A liquid crystal drive circuit, comprising: 2. The liquid crystal drive circuit according to claim 1, wherein said correction circuit includes a gamma signal amplifier circuit for compensating for linearity of light transmission characteristics of said liquid crystal. 3. The liquid crystal drive circuit according to claim 1, wherein the correction circuit includes a drive adjustment circuit for compensating a contrast characteristic of the liquid crystal. 4. The liquid crystal driving circuit according to claim 1, wherein the correction circuit includes a cutoff adjusting circuit for compensating the luminance characteristics of the liquid crystal. 5. A video signal and a first control signal are inputted, and linearity in light transmission characteristics of liquid crystal and temperature dependency of the linearity are compensated according to the first control signal, and a gamma-corrected signal is obtained. A gamma signal amplifying circuit to be provided; a polarity inversion circuit for converting the gamma-corrected signal into an AC inversion signal required for driving a liquid crystal; inputting the AC inversion signal and a second control signal; A drive adjustment circuit for compensating the contrast characteristic and the temperature dependency of the contrast characteristic according to the second control signal and providing a contrast-corrected signal; and receiving the contrast-corrected signal and a third control signal. And a cut-off adjustment method for compensating a luminance characteristic in a light transmission characteristic of a liquid crystal and a temperature dependence of the luminance characteristic according to a third control signal, and providing a luminance-corrected signal. A liquid crystal module that displays an image corresponding to the luminance-compensated signal using the liquid crystal; a temperature detection circuit that detects an ambient temperature and provides a signal corresponding to the ambient temperature; A corresponding signal is converted into a signal in a voltage range suitable for each of the gamma signal amplifier circuit, the drive adjustment circuit, and the cutoff adjustment circuit, thereby generating the first to third control signals, and a voltage to be provided to each circuit. A liquid crystal display device comprising: a conversion circuit.