JP2000148072A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress deterioration in display quality by varying contrast of a picture linked with brightness adjustment of backlight, and thereby compensating apparent lowering in contrast when the brightness decreases. SOLUTION: A backlight 10 of a TFT liquid crystal display panel 1 is light- modulated by driving an inverter circuit 9 with light-modulating pulses from a light-modulating circuit 8. The light-modulating pulses are also supplied to a gain adjustment conversion circuit 5a in a video chroma processing circuit 5, and a video signal gain is increased as the on-off duty ratio of the pulses is decreased, and thereby the apparent lowering in contrast of a display picture is prevented when the brightness of the backlight decreases.

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 including a transmission type liquid crystal display panel having a backlight, and more particularly to an improvement for reducing a change in contrast of a displayed image due to a decrease in luminance of the backlight. .

[0002]

2. Description of the Related Art FIG. 6 shows a schematic structure of a conventional transmission type liquid crystal display device. In the figure, 1 is a TFT liquid crystal display panel, 2 is a gate side driver, 3 is a source side driver, 1
Reference numeral 0 denotes a backlight, which constitutes the LCD module 1a. 4 is an LCD controller, 5 is a video chroma processing circuit, 6 is a VCOM amplifier, 7 is a DC / DC converter, 8 is a dimming circuit, and 9 is an inverter circuit.

When the video signal 14 is input to the video chroma processing circuit 5, each of the synchronizing signals such as H, V, CSYNC, etc.
The video signal 14 output to the CD controller 4 and input is separated into R, G, and B signals, and the frame synchronization signal 12
Is output to the source side driver 3 at a timing based on the horizontal synchronizing signal H input from the LCD controller 4 as a display drive signal. Also, the LCD controller 4 generates various control signals for controlling the driving of the gate-side driver 2 and the source-side driver 3, outputs the control signals to the gate-side driver 2 and the source-side driver 3, and outputs a VCOM signal through the VCOM amplifier 6.
A COM signal is applied to a common electrode of the TFT liquid crystal display panel 1.

A DC / DC converter 7 generates a power supply for each signal processing system by applying a VCC power supply.
To the specified power supply. The backlight 10 is disposed behind the TFT liquid crystal display panel 1 in the LCD module 1a. The dimming circuit 8 generates a dimming pulse 11,
The pulse is supplied to the inverter circuit 9 to dimme the backlight 10.

[0005]

In the liquid crystal display device described above, dimming of the backlight 10 is performed by turning on / off an inverter transformer in the inverter circuit 9 with a dimming pulse to change the on-time. By P
This is performed by WM (pulse width modulation) dimming. However, the relationship between the display luminance of the liquid crystal display panel and the input voltage (input video signal amplitude) has characteristics as shown in FIG. That is, when the luminance of the backlight 10 is dimmed to reduce the luminance from a high luminance state, the change in the display luminance with respect to the input voltage becomes gradual particularly in the halftone luminance region, and the contrast of the display image of the liquid crystal display panel 1 is increased. Will appear to have dropped significantly. As described above, when the brightness of the backlight is reduced, there is a problem that the display quality is felt to be greatly reduced more than the brightness is reduced.

An object of the present invention is to provide a liquid crystal display device,
To provide a configuration in which the contrast of a display image is changed in conjunction with the brightness adjustment of a backlight to compensate for an apparent decrease in contrast when the brightness is reduced and to suppress a reduction in display quality. It is in.

[0007]

In order to achieve the above object, a liquid crystal display device according to the present invention comprises a backlight brightness adjusting means, and as the brightness of the backlight is reduced by the adjusting means, the halftone of a displayed image is reduced. In order to increase the contrast in the area, the display luminance of the display driving signal with respect to the input video signal is increased so as to increase the display luminance of the area where the display luminance is high in the halftone display area and to decrease the display luminance of the area where the display luminance is low. And a gain adjusting means for adjusting.

In the liquid crystal display device according to the present invention, the luminance adjusting means includes a dimming circuit for generating a luminance dimming pulse, and the gain adjusting means controls an on / off duty ratio of the luminance dimming pulse. The gain of the display drive signal with respect to the input video signal may be adjusted accordingly.

[0009]

FIG. 1 shows a schematic configuration of an embodiment of a transmission type liquid crystal display device of the present invention. In the figure, 1 is a TFT liquid crystal display panel, 2 is a gate side driver, 3 is a source side driver, 10 is a backlight, and these are LCs.
The D module 1a is configured. 4 is an LCD controller, 5 is a video chroma processing circuit, 6 is a VCOM amplifier,
7, a DC / DC converter; 8, a dimming circuit; and 9, an inverter circuit. In addition, the dimming pulse 11 is supplied to the inverter circuit 9 and also to the video chroma processing circuit 5 as compared with the conventional example of FIG.

FIG. 2 shows a schematic internal configuration of the video chroma processing circuit. As shown in the figure, when the video signal 14 is input to the video chroma processing circuit 5, H, V, CSYNC
Output to the LCD controller 4 and separates the input video signal 14 into R, G, B signals.
An inverted RGB signal 13 inverted based on the frame synchronization signal 12 is output to the source driver 3 at a timing based on the horizontal synchronization signal H input from the LCD controller 4 as a display drive signal. Further, the LCD controller 4 generates various control signals for controlling the driving of the gate side driver 2 and the source side driver 3, and outputs the generated signals to the gate side driver 2 and the source side driver 3.
The VCOM signal is applied to the common electrode of the TFT liquid crystal display panel 1 via the M amplifier 6.

A DC / DC converter 7 generates a power supply for each signal processing system by applying a VCC power supply.
To the specified power supply. The backlight 10 is disposed behind the TFT liquid crystal display panel 1 in the LCD module 1a. The dimming circuit 8 generates a dimming pulse 11,
The pulse is supplied to the inverter circuit 9 to dimme the backlight 10.

In the liquid crystal display device described above, the dimming of the backlight 10 is performed by PWM (pulse width modulation) by turning on / off the inverter transformer in the inverter circuit 9 by a dimming pulse to change the on-time. ) Dimming is performed.

That is, as shown in FIG. 3, the dimming pulse has, for example, a frequency f = 100 to 2 kHz and an amplitude of 0 to 0 kHz.
5V, and its ON period is a backlight lighting region, and its OFF period is a backlight OFF region. When the duty ratio is 100% during the on-period, continuous lighting is performed and the brightness is at the maximum, and the backlight is turned off when the duty ratio is 0% during the on-period. When dimming the backlight in this way, in order to compensate for the apparent decrease in the contrast of the display image when dimming the backlight and lowering the luminance as described above, the present invention employs the above-described dimming. The light pulse is also applied to the video chroma processing circuit 5 to change the gain of the display drive signal with respect to the input video signal in conjunction with the ratio of the duty ratio of the ON period of the light control pulse. A function is added to increase the gain so as to increase the contrast in the halftone region of the display image when the brightness of the light 10 is reduced, and to suppress the apparent decrease in the contrast of the display image.

FIG. 2 shows a successful example of a video chroma processing circuit for performing the above functions. As shown in the figure, a gain adjustment conversion circuit 5a is added between a gain adjustment circuit 5b and a contrast adjustment circuit 5c normally provided in the video chroma processing circuit 5, and the dimming control circuit 5a is added to the gain adjustment conversion circuit 5a. The above function is achieved by applying the pulse 11 and increasing the gain of the video signal as the duty ratio of the ON period of the dimming pulse 11 decreases. The gain adjustment conversion circuit 5a may be built in the video chroma processing circuit 5. With such a configuration, as shown in FIG. 4, the gain of the video signal is increased as the duty ratio decreases with reference to the gain of the video signal at the time of inputting the dimming pulse having the duty ratio of 100%. The gain is adjusted in a direction to increase the contrast in the halftone area. The relationship between the display luminance of the liquid crystal display panel and the input voltage (input video signal amplitude) by this gain adjustment is set to have the characteristics shown in FIG. That is, as described above, when the backlight luminance shown in FIG. 7 is reduced, the change in the display luminance with respect to the input voltage in the halftone luminance area becomes gradual, and the characteristic of the portion where the apparent contrast is reduced is corrected. Then, the luminance in the high display luminance area is increased, and the display luminance in the low display luminance area is increased so that the change in the display luminance with respect to the input voltage in the halftone luminance area is substantially the same as when the backlight luminance is high. Is changed to decrease. Thereby, the correction is made so that the apparent decrease in the contrast of the displayed image is reduced. Thus, the gain of the display drive signal with respect to the input video signal,
That is, by changing the contrast in the halftone region in conjunction with the brightness adjustment of the backlight, it is possible to suppress a decrease in display quality due to a reduction in the brightness of the backlight.

In addition, in the case of such a configuration, it is possible to link the video signal and the dimming pulse, thereby making it possible to synchronize the lighting timing of the backlight with the display timing of the display image. This also has the effect of reducing dimming noise.

[0016]

As described above, according to the present invention, even when the brightness of the backlight is changed to increase or decrease the brightness to change the brightness, the change in the apparent contrast of the displayed image is small. In other words, the deterioration of the display quality can be suppressed, so that the allowable range of the brightness control of the backlight can be expanded. In addition, by synchronizing the cycle of the video signal and the dimming pulse, dimming noise due to synchronization deviation is reduced.

[Brief description of the drawings]

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

FIG. 2 is a block diagram illustrating a configuration example of a video chroma processing circuit in FIG. 1;

FIG. 3 is a waveform diagram showing a dimming pulse.

FIG. 4 is a characteristic diagram showing a relationship between a duty ratio of an ON period of a dimming pulse and an output amplitude of a video signal.

FIG. 5 is a characteristic diagram showing a relationship between an input video signal amplitude voltage and display luminance in the present invention.

FIG. 6 is a block diagram illustrating a schematic configuration of a conventional liquid crystal display device.

FIG. 7 is a characteristic diagram showing a relationship between input signal amplitude voltage and display luminance of a conventional liquid crystal display panel.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 TFT liquid crystal display panel 2 Gate side driver 3 Source side driver 4 LCD controller 5 Video chroma processing circuit 5a Gain adjustment conversion circuit 8 Dimming circuit 9 Inverter circuit 10 Backlight

Claims (2)

[Claims] 1. A backlight luminance adjusting means, and a display luminance is high in a halftone display area so that a contrast in a halftone area of a display image is increased as the luminance of the backlight is reduced by the adjusting means. A liquid crystal display device comprising: gain adjustment means for adjusting a gain of a display drive signal with respect to an input video signal so as to increase display luminance in an area and decrease display luminance in an area with low display luminance. 2. The luminance adjusting means includes a dimming circuit for generating a luminance dimming pulse, and the gain adjusting means adjusts an input video signal according to an on / off duty ratio of the luminance dimming pulse. 2. The liquid crystal display device according to claim 1, wherein the gain of the display drive signal is adjusted.