KR20080062874A - Liquid crystal display - Google Patents

Abstract

An LCD device is provided to generate a Vcom having a voltage value varied according to the temperature change of an LCD panel, thereby preventing that display quality is deteriorated as a Vcom value is changed by the temperature change of the LCD panel. Liquid crystal cells are formed in a matrix form in an LCD(Liquid Crystal Display). A data driving unit(12) supplies data to the data lines(D1~Dm) of the LCD panel. A gate driver(14) supplies a scan signal to gate lines. A DC-DC(Direct Current) converter(16) outputs driving voltages of the LCD panel. A common voltage generator of a temperature adaptive type is connected to the DC-DC converter. A timing controller(22) controls the data driver, the gate driver, and a common voltage compensator. The common voltage generator controls a Vcom(common Voltage) according to the temperature of the LCD panel to generate a compensated Vcom and apply the generated Vcom to the LCD panel.

Description

Liquid Crystal Display

1 and 2 are circuit diagrams showing a common voltage generator of a conventional liquid crystal cell and a liquid crystal display device.

3 is a view showing a liquid crystal display device according to the present invention.

4 is a circuit diagram illustrating a common voltage generator according to a first embodiment of the present invention.

5 is a circuit diagram illustrating a common voltage generator according to a second exemplary embodiment of the present invention.

<Description of Symbols for Main Parts of Drawings>

10: liquid crystal panel 12: data driver

14 gate driver 16 DC-DC converter

18: common voltage compensator 22: timing controller

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device capable of generating a common voltage having a stable voltage value even when the panel temperature changes.

The liquid crystal display device displays an image by adjusting the light transmittance of the liquid crystal using an electric field. To this end, the liquid crystal display includes a liquid crystal panel in which pixel regions are arranged in a matrix, and a driving circuit for driving the liquid crystal panel.

As illustrated in FIG. 1, the liquid crystal panel has a gate area GL and a data line DL intersected and a pixel area defined by the gate line GL and the data line DL intersected. A thin film transistor (TFT) for driving the liquid crystal cell and a storage capacitor Cst for maintaining the voltage of the liquid crystal cell are formed in the pixel region.

The liquid crystal cell adjusts the amount of light transmitted while the array of liquid crystal molecules is deflected by an electric field applied to the liquid crystal layer when a data voltage is applied to the pixel electrode 11 and a common voltage Vcom is applied to the common electrode 12. Express gradation.

Among them, the common voltage generator for generating the common voltage includes the circuit diagram of FIG. 2.

2, a conventional common voltage generator includes a VDD voltage supply terminal VDD receiving a VDD voltage provided from a power supply unit, a first resistor R1 having one end connected to the VDD voltage supply terminal VDD, The second resistor R2 connected at one end to the first node n1 connected to the other end of the first resistor R1, the variable resistor VR connected in series with the second resistor R2, and the first node n1. The first capacitor C1 formed between the second node n2 branched from the third node and the third node connected to one end of the variable resistor VR, and the fourth node n4 branched from the second node n2. And a second capacitor C2 formed between the third node n3 and the common voltage output terminal Vcom_P connected to the fourth node n4.

The common voltage generator divides the VDD voltage provided from the power supply unit through the RC circuit including the first to third resistors R1, R2, and R3, the variable resistor VR, and the capacitors C1 and C2, and then the common voltage. Create (Vcom). The common voltage Vcom is output through the common voltage output terminal Vcom_P.

The common voltage Vcom generated at this time is fixed to a value output by the resistor distribution circuit that is initially set. The common voltage value is set to a value suitable for driving in a temperature range of about 50 ° C at room temperature.

However, in the process of driving the liquid crystal display, the temperature of the panel due to the backlight may be greatly increased. In addition, as the use range of the liquid crystal display device increases, the driving of the outdoor device increases, and thus the temperature of the panel becomes higher due to the influence of the external temperature.

As the temperature of the panel rises, the load of the panel rises and the response characteristic of the liquid crystal cell changes, thereby increasing the common voltage value.

Since the gray scale expression of the liquid crystal panel is determined by the degree of deflection of the liquid crystal due to the difference between the common voltage and the data voltage, the change of the common voltage eventually impairs the desired gray scale expression and degrades the image quality.

Accordingly, an object of the present invention is to provide a liquid crystal display device capable of supplying a stable common voltage even when a temperature change of a panel occurs.

In order to achieve the above object, a liquid crystal display according to the present invention is a liquid crystal panel having a pixel region defined where the data line and the gate line intersect, a pixel electrode and a common electrode formed in the pixel region, and driving the data line. A data driver for driving the gate line, a gate driver for driving the gate line, and a voltage applied to the common electrode. The data driver includes at least two resistors and is connected in parallel with any one of the resistors. And a temperature-adaptive common voltage generator of the voltage distribution circuit including the thermistor.

At this time, it is preferable to use the thermistor which has a negative resistance temperature coefficient characteristic.

An example of the common voltage generator includes a first resistor connected to a VDD voltage source, a second resistor branched from a first node connected to the other end of the first resistor, and a thermistor connected in parallel to the second resistor. It can be implemented as a circuit diagram.

In the present embodiment, a variable resistor connected in series with the second resistor, a first capacitor formed between the second node branched from the first node and a third node connected to one end of the mask resistor, and the second node The display device may further include a second capacitor formed between the branched fourth node and the third node, and a common voltage output terminal connected to the fourth node.

In another embodiment, the common voltage compensator may further include a parallel resistor connected in parallel with the variable resistor.

Other objects and features of the present invention in addition to the above object will be apparent from the description of the embodiments with reference to the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 3 to 5.

3 is a view showing a liquid crystal display device according to the present invention.

Referring to FIG. 3, in the liquid crystal display according to the present invention, a liquid crystal cell Clc is formed in a region where m data lines D1 to Dm and n gate lines G1 to Gn intersect, whereby m × n Liquid crystal panel 10 having a plurality of liquid crystal cells Clc formed in a matrix type, a data driver 12 for supplying data to data lines D1 to Dm of the liquid crystal panel 10, and gate lines A gate driver 14 for supplying a scan signal to G1 to Gn, a DC-DC converter (hereinafter, DC-DC converter) 16 and DC-DC converter 16 for generating driving voltages of the liquid crystal panel 10. And a temperature controller 22 for controlling the temperature-adaptive common voltage generator 18 and the data driver 12, the gate driver 14, and the common voltage compensator 20.

The liquid crystal panel 10 has a structure in which a liquid crystal is injected between two light transmitting substrates. The data lines D1 to Dm and the gate lines G1 to Gn cross each other on the lower substrate of the liquid crystal panel 10. A thin film transistor TFT is formed at the intersection of the data lines D1 to Dm and the gate lines G1 to Gn, and the TFT is a data line in response to a scan signal from the gate lines G1 to Gn. The data of (D1 to Dm) is supplied to the liquid crystal cell Clc. For this purpose, the gate electrode of the TFT is connected to the corresponding gate lines G1 to Gn, and the source electrode is connected to the corresponding data lines D1 to Dm. The drain electrode of the TFT is connected to the pixel electrode of the liquid crystal cell Clc. The black matrix, the color filter, and the common electrode are formed on the upper substrate of the liquid crystal panel 10. A polarizing plate having an optical axis orthogonal to each other is attached to the upper substrate and the lower substrate of the liquid crystal panel 10, and an alignment layer for setting the pretilt angle of the liquid crystal is formed on the inner side of the liquid crystal panel 10 in contact with the liquid crystal. The storage capacitor Cst formed in each of the liquid crystal cells Clc is formed between the pixel electrode of the liquid crystal cell Clc and the front gate line, or is formed between the pixel electrode of the liquid crystal cell Clc and the common electrode line. It serves to keep the voltage of Clc) constant.

The data driver 12 receives the data control signal DDC from the timing controller 22 and supplies the digital video data RGB to the data lines D1 to Dm corresponding to the grayscale value.

The DC-DC converter 16 boosts or decompresses a VCC voltage applied from a system (not shown) to generate a gamma voltage, a gate high voltage (Vgh), and a gate low voltage (Vgl) generated by a divided voltage of a VDD voltage of 6V or more and a VDD voltage. Etc. The VDD voltage and the gamma voltage GammaV are supplied to the data driver 12 as analog gamma voltages. The gate high voltage Vgh is supplied to the gate driver 14 as the high logic voltage of the scan pulse set above the threshold voltage of the TFT and the gate low voltage Vgl is the low logic voltage of the scan pulse set to the off voltage of the TFT. It is supplied to the drive part 14.

The timing controller 22 generates a gate control signal GDC for controlling the gate driver 14 and a data control signal DDC for controlling the data driver 12 by using a vertical / horizontal synchronization signal and a clock signal. do. The gate control signal GDC includes a gate start pulse GSP. The data control signal DDC includes a source start pulse (CSP), a source shift clock (SSC), a source output signal (SOE), a polarity signal (POL), and the like. do. The timing controller 22 rearranges the digital video data RGB and supplies the digital video data RGB to the data driver 12.

The temperature-adaptive common voltage generator 18 generates a common voltage by inputting the VDD voltage and amplifying the VDD voltage with an operational amplifier. In particular, the common voltage generator 18 according to the present invention generates the corrected common voltage Vcom by applying the common voltage Vcom to the panel by adjusting the common voltage Vcom according to the temperature of the liquid crystal panel 10.

The conventional common voltage generator outputs only a constant common voltage as a voltage value divided by a resistor divider circuit, but the temperature-adaptive common voltage generator 18 according to the present invention has at least any one of two or more resistors in a divider circuit. By connecting thermistors in parallel to one resistor, they generate a compensated common voltage in the event of temperature changes. A detailed description thereof will be described below with reference to the drawings.

4 is a circuit diagram showing the temperature adaptation common voltage generation unit 18 according to the first embodiment of the present invention.

Referring to FIG. 4, one end of the VDD voltage supply terminal VDD and the VDD voltage supply terminal VDD supplied with the VDD voltage provided from the power supply unit of the temperature adaptive common voltage generator 18 according to the first embodiment of the present invention. A variable connected in series with the connected first resistor R1, the second resistor R2 connected at one end to the first node n1 connected to the other end of the first resistor R1, and the second resistor R2. First capacitor C1 and second node n2 formed between the resistor VR, the second node n2 branching from the first node n1, and the third node connected to one end of the variable resistor VR. A second capacitor C2 formed between the fourth node n4 and the third node n3 branched from the second node), and a common voltage output terminal Vcom_P connected to the fourth node n4.

The thermistor TH is formed in parallel with the second resistor R2 between the first node between the first and second resistors R2 and one end of the second resistor R2. Thermistor TH uses a device having a characteristic of negative temperature coefficient (NTC) in which the resistance value decreases as the temperature increases.

The thermistor TH corrects the variation of the voltage value of the common voltage Vcom according to the panel temperature. That is, as the temperature of the panel increases, the resistance value of the thermistor TH decreases, so that the common voltage Vcom decreases. When the panel temperature decreases, the resistance value of the thermistor TH increases, so the common voltage Vcom increases. .

As a result, the common voltage Vcom is changed due to the temperature change of the panel, thereby preventing the display quality from being lowered.

4 is a circuit diagram showing the temperature adaptation common voltage generation unit 68 according to the second embodiment.

Referring to FIG. 4, the temperature-adaptive common voltage generator 68 may include a first VDD voltage supply terminal VDD receiving a VDD voltage provided from a power supply unit, and a first end connected to the VDD voltage supply terminal VDD. Variable resistor VR connected in series with resistor R1, second resistor R2 connected at one end to first node n1 formed at the other end of first resistor R1, and second resistor R2. The first capacitor C1 is formed between the second node n2 branched from the first node n1 and the third node formed at the other end of the variable resistor VR, and branched from the second node n2. The second capacitor C2 formed between the fourth node n4 and the third node n3 and the common voltage output terminal Vcom_P connected to the fourth node n4 are provided.

The thermistor TH connected in parallel with the second resistor R2 between the first node between the first and second resistors R2 and one end of the second resistor R2, and the variable resistor VR. The third resistor R3 is connected in parallel. Thermistor TH uses a device having a characteristic of negative temperature coefficient (NTC) in which the resistance value decreases as the temperature increases.

The thermistor TH corrects the variation of the voltage value of the common voltage Vcom according to the panel temperature. That is, as the temperature of the panel increases, the resistance value of the thermistor TH decreases, so that the common voltage Vcom decreases. When the panel temperature decreases, the resistance value of the thermistor TH increases, so the common voltage Vcom increases. .

The third resistor R3 connected in parallel with the variable resistor VR compensates for the change in the resistance value of the thermistor TH. If the temperature change of the panel is large, the resistance value of the thermistor may change abruptly, thereby causing an abnormality in image display. In order to prevent this, the third resistor R3 is connected to the thermistor TH to prevent the common voltage from being rapidly changed due to the rapid change in the resistance of the thermistor.

As described above, the liquid crystal display according to the present invention generates a common voltage having a voltage value that changes according to the temperature change of the panel. As a result, the load applied to the panel is changed according to the temperature change, and the common voltage value is compensated for.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (6)

A liquid crystal panel formed in each of the regions separated by the data line and the gate lines and including pixel cells commonly connected to the common electrode line; A driving unit driving the liquid crystal panel in response to video data; And a temperature-adaptive common voltage generator for supplying a common voltage which is varied according to temperature in the liquid crystal panel to the common electrode line of the liquid crystal panel. The method of claim 1, The temperature-adaptive common voltage generator includes a temperature-adaptive common voltage generator of a voltage distribution circuit including a thermistor connected in parallel with a resistor of any one of the resistors and connected to a VDD voltage source. A liquid crystal display device. The method of claim 2, The common voltage generator A first resistor coupled with the VDD voltage source; A second resistor branched at a first node connected to the other end of the first resistor; And a thermistor connected in parallel to said second resistor. The method of claim 3, wherein A variable resistor connected in series with the second resistor; A first capacitor formed between a second node branched from the first node and a third node connected to one end of a mask resistor; A second capacitor formed between the fourth node and the third node branched from the second node; And a common voltage output terminal connected to the fourth node. The method of claim 4, wherein And the common voltage compensator further comprises a parallel resistor connected in parallel with the variable resistor. The method according to any one of claims 2 to 5, And the thermistor has a negative resistance temperature coefficient characteristic.

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