JPH07175447A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide a liquid crystal display device which does not neccesitate an AC driving circuit by eliminating the disadvantage of conventionally making a liquid crystal driving circuit large-sized. CONSTITUTION:This device is constituted of an A/D converter 1 A/D converting a video signal demodulated by a tuner part, a gamma correction circuit 2 gamma correcting the output of the A/D converter 1 and having the look up table of two kinds of data of ordinary gamma correction data and the data of value obtained by the polarity inversion of the correction value, a control part 5 controlling the gammacorrection circuit 2, a D/A converter 3 D/A converting the output of the gammacorrection circuit 2 and a clamp up circuit 4; and is also constituted so as to invert the polarity of voltage to be applied to the liquid crystal every one field.

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,
More specifically, the present invention relates to a drive circuit that drives liquid crystal.

[0002]

2. Description of the Related Art Among commercially available liquid crystal displays, the cell structure of what is called a TN (twisted nematic) type has a cell structure in which a liquid crystal is sealed in a gap of about 10 μm composed of a common substrate and a segment substrate. Each of the glass substrates is coated with a transparent electrode, and surface treatment is performed so that rod-like molecules of liquid crystal are aligned parallel to the glass substrate under no electric field. The orientation directions of the two glass substrates are shifted from each other by 90 °, and two polarizing plates are attached to both outer surfaces of the substrates according to the orientation directions of the respective glass substrates. When the electric field is not applied between the transparent electrodes, the liquid crystal molecules are processed so as to be aligned parallel to the surfaces of the two glass substrates, so that the liquid crystal molecules are twisted by 90 ° and aligned. There, the incident light rotates through 90 ° and can pass through the polarizing plates positioned so that they are at right angles to each other, and the cell structure is observed as a transparent body. On the other hand, when an electric field is applied, the liquid crystal molecules are aligned parallel to the direction of the electric field, so that light cannot pass through the polarizing plate and the cell structure of the liquid crystal becomes opaque. Using the negative dielectric constant anisotropic property of the liquid crystal as described above, the amount of transmitted light is adjusted by adjusting the electric field strength applied to the liquid crystal, and an image is displayed on a television or the like. It is used to drive display devices. That is,
This display has good extinction in the OFF state,
In order to increase the contrast, the liquid crystal molecules were oriented perpendicular to the display panel surface when no voltage was applied so that they were at right angles to each other. However, if the electric field is continuously applied to the liquid crystal only in one direction, the life of the liquid crystal cell is shortened accordingly. Therefore, conventionally, the direction of the electric field applied to the liquid crystal cell is switched for each field of the video signal by the AC drive circuit as shown in FIG.
This is intended to prolong the life of the liquid crystal cell. In the figure, 41 is a first NPN transistor,
The video signal 48 is input to the base 43, the second NPN transistor 42 is connected to the collector, and the switch 4
The output from the emitter of the first NPN transistor 41 is connected to the terminal 45 of No. 4, and the terminal 46 of the switch 44 is connected.
Is connected to the output from the emitter of the second NPN transistor 42, the switch 44 is alternately switched for each field, and the polarities of the signal levels of the respective fields are inverted. However, the above-mentioned conventional liquid crystal drive circuit has a drawback that it requires an AC drive circuit such as the first and second transistors and the like, the circuit configuration becomes large, and miniaturization of the circuit is hindered. .

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid crystal display device which does not require an AC drive circuit by eliminating the drawback of increasing the size of a conventional liquid crystal drive circuit as described above.

[0004]

In order to solve the above problems, the present invention provides an A / D converter for A / D converting a video signal demodulated by a tuner section, and an output of the A / D converter by γ A γ correction circuit having a look-up table of two types of data, that is, normal γ correction data and data of a value obtained by reversing the polarity of the correction value, and a control unit that controls the γ correction circuit. It is composed of a D / A converter for D / A converting the output of the γ correction circuit and a clamp-up circuit, and is configured to invert the polarity of the voltage applied to the liquid crystal at least every one field.

[0005]

Since the liquid crystal display device according to the present invention has the above-described structure, the γ correction circuit includes the normal γ correction data and the data obtained by reversing the polarity of the correction value.
Since it is stored as a look-up table of data of various types, the control unit switches the respective tables at the periods of the horizontal and vertical synchronizing signals of the video signal, and the look-up tables of the γ correction circuit 2 are respectively changed. The reading is performed alternately, so that the γ correction and the polarity reversing operation can be simultaneously performed.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a circuit configuration of a liquid crystal display device according to the present invention will be described with reference to the drawing. In FIG. 1, reference numeral 1 is an A / D converter, which is a video signal demodulated by a tuner section (not shown). / D conversion. The output of the A / D converter is connected to the γ correction circuit 2, the γ correction circuit is connected to the control unit 5, and this output is further connected to the D / A converter 3. This D /
The output of the A converter 3 is connected to the clamp-up circuit 4 and output to the liquid crystal drive circuit.

Next, the operation of the liquid crystal display device according to the present invention will be described with reference to FIG. 1. In FIG.
A look-up table of two types of data, that is, normal γ correction data and data of a value obtained by reversing the polarity of this correction value, is stored. The control unit 5 switches the respective tables at the cycle of the horizontal and vertical synchronizing signals of the video signal, alternately reads out the look-up tables of the γ correction circuit 2, thereby reversing the γ correction and the polarity. Let them perform actions at the same time. In the figure, (a), (b),
Each of the output waveforms shown in (c) has the same sign as that in FIG. 2. In FIG. 2, (a) shows the input signal 21 input to the A / D converter 1 from the low luminance portion. In the case of a waveform that linearly changes up to the high-intensity part, by performing γ correction on this signal, the level of one low-intensity part is raised to 22 as shown in FIG. The high-brightness portion has a lowered level like 23, and by inputting these signals to the clamp-up circuit, the respective DC operation levels are converted as shown in FIG. The drive signal level 22 on the one side is output as a signal 25, and the drive signal level 23 on the other side is output as a signal in which the polarities are inverted, as in 26. When this output is applied to the liquid crystal panel, as shown in FIG. 3, the orientation direction of the liquid crystal cell between the two electrode plates 31 and 32 is such that the direction of the applied electric field is based on the earth level 38. For example, if the direction of the arrow 34 is the same as the arrow 35, and if the direction of the applied electric field is the direction of the arrow 36, the opposite directions are the same as the arrow 37. In this way, the applied electric field is AC-driven and switched for each field, so that the life of the liquid crystal cell can be extended.

[0008]

Since the present invention is configured as described above, the present invention does not require an AC drive circuit as in the conventional case.
The circuit can be downsized, and the life of the liquid crystal can be extended.

[Brief description of drawings]

FIG. 1 is a block diagram of a circuit of a liquid crystal display device according to the present invention.

FIG. 2 is an explanatory diagram of a liquid crystal drive signal of the liquid crystal display device according to the present invention.

FIG. 3 is a diagram illustrating an operation of driving liquid crystal by the liquid crystal display device according to the present invention.

FIG. 4 is an explanatory diagram of an AC drive circuit in a conventional liquid crystal display device.

[Explanation of symbols]

 1 A / D converter 2 γ correction circuit 3 D / A converter 4 Clamp-up circuit 5 Control unit

Claims (3)

[Claims] 1. A γ correction circuit having a liquid crystal cell in which voltages of two kinds of positive and negative polarities are alternately applied, and a look-up table of two kinds of video signal data corresponding to the two kinds of polarities. A liquid crystal display device comprising: a control unit for controlling the γ correction circuit; a D / A converter for D / A converting the output of the γ correction circuit; and a clamp-up circuit. 2. The liquid crystal display device according to claim 1, wherein the voltage applied alternately is switched by a horizontal synchronizing signal. 3. The liquid crystal display device according to claim 1, wherein the switching of the voltage applied alternately is performed by a vertical synchronizing signal.