KR101263501B1 - LCD and drive method thereof - Google Patents

Abstract

The present invention provides a liquid crystal display device capable of varying the level of the minimum threshold voltage, which is a control voltage of the common voltage level supplied to the liquid crystal display panel, according to the ambient temperature, wherein a common electrode is formed in the liquid crystal cell of each pixel. A liquid crystal display panel; Minimum voltage generation means generated by varying a minimum voltage as a reference for controlling a common voltage level according to a temperature change around the liquid crystal display panel; Common voltage adjusting means for adjusting a common voltage level according to the minimum voltage level generated by said minimum voltage generating means; And common voltage generating means for supplying a common voltage having a level controlled by the common voltage adjusting means to the common electrode.

LCD, Thermistor, Common Voltage, Minimum Voltage, Temperature

Description

Liquid crystal display device and driving method thereof

1 is an equivalent circuit diagram of a pixel formed in a general liquid crystal display device.

2 is a block diagram of a conventional liquid crystal display device.

3 is a block diagram of a liquid crystal display device according to an embodiment of the present invention.

4 is a circuit diagram of a minimum voltage generator in FIG. 3.

FIG. 5 is a circuit diagram of a common voltage generator of FIG. 3. FIG.

6 is a flowchart illustrating a method of driving a liquid crystal display device according to an exemplary embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

100 and 200: liquid crystal display device 110: liquid crystal display panel

120: data driver 130: gate driver

150: backlight assembly 160: inverter

170: common voltage generator 180: gate driving voltage generator

190: timing controller 210: minimum voltage generator

220: common voltage controller 230: common voltage generator

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and a method of driving the liquid crystal display device capable of varying the level of the minimum threshold voltage, which is a control point of the common voltage level supplied to the liquid crystal display panel, according to the ambient temperature. .

The liquid crystal display device displays an image by adjusting the light transmittance of the liquid crystal cells according to the video signal, and the active matrix type liquid crystal display device in which the switching elements are formed for each liquid crystal cell enables active control of the switching elements. This is advantageous for video implementation. As a switching device used in the active matrix liquid crystal display device, a thin film transistor (hereinafter, referred to as TFT) is mainly used as shown in FIG. 1.

Referring to FIG. 1, an active matrix type liquid crystal display device converts digital input data into an analog data voltage based on a gamma reference voltage and supplies it to the data line DL and simultaneously supplies scan pulses to the gate line GL. The liquid crystal cell Clc is charged.

The gate electrode of the TFT is connected to the gate line GL, the source electrode is connected to the data line DL, and the drain electrode of the TFT is connected to the pixel electrode of the liquid crystal cell Clc and one electrode of the storage capacitor Cst. Connected.

A common voltage Vcom is supplied to the common electrode of the liquid crystal cell Clc.

The storage capacitor Cst serves to charge the data voltage applied from the data line DL when the TFT is turned on to maintain the voltage of the liquid crystal cell Clc constant.

When a scan pulse is applied to the gate line GL, the TFT is turned on to form a channel between the source electrode and the drain electrode to apply a voltage on the data line DL to the pixel electrode of the liquid crystal cell Clc Supply. At this time, the liquid crystal molecules of the liquid crystal cell Clc modulate the incident light by changing the arrangement by the electric field between the pixel electrode and the common electrode.

A configuration of a conventional liquid crystal display device having pixels having such a structure will be described with reference to FIG. 2.

2 is a block diagram of a conventional liquid crystal display device.

Referring to FIG. 2, the liquid crystal display 100 according to the related art includes a thin film transistor for driving the liquid crystal cell Clc at the intersection of the data lines DL1 to DLm and the gate lines GL1 to GLn. TFT: a thin film transistor (110) having a thin film transistor (110), a data driver (120) for supplying data to the data lines (DL1 to DLm) of the liquid crystal display panel 110, the liquid crystal display panel 110 A gate driver 130 for supplying scan pulses to the gate lines GL1 to GLn of the gate lines, a gamma reference voltage generator 140 for generating a gamma reference voltage and supplying it to the data driver 120, and a liquid crystal display panel The backlight assembly 150 for irradiating light to the 110, the inverter 160 for applying an alternating voltage and current to the backlight assembly 160, and the common voltage Vcom are generated to generate the liquid crystal display panel 110. The common voltage generator 170 for supplying the common electrode of the liquid crystal cell Clc In addition, the gate driving voltage generator 180 for generating the gate high voltage VGH and the gate low voltage VGL to supply the gate driver 130, and controls the data driver 120 and the gate driver 130. The timing controller 190 is provided.

In the liquid crystal display panel 110, liquid crystal is injected between two glass substrates. On the lower glass substrate of the liquid crystal display panel 110, the data lines DL1 to DLm and the gate lines GL1 to GLn are orthogonal. TFTs are formed at intersections of the data lines DL1 to DLm and the gate lines GL1 to GLn. The TFT supplies the data on the data lines DL1 to DLm to the liquid crystal cell Clc in response to the scan pulse. The gate electrodes of the TFTs are connected to the gate lines GL1 to GLn, and the source electrodes of the TFTs are connected to the data lines DL1 to DLm. The drain electrode of the TFT is connected to the pixel electrode of the liquid crystal cell Clc and the storage capacitor Cst.

The TFT is turned on in response to the scan pulse supplied to the gate terminal via the gate lines GL1 to GLn. When the TFT is turned on, video data on the data lines DL1 to DLm is supplied to the pixel electrode of the liquid crystal cell Clc.

The data driver 120 supplies data to the data lines DL1 to DLm in response to the data driving control signal DDC supplied from the timing controller 190, and digital video data supplied from the timing controller 190. After sampling and latching the RGB, the liquid crystal cell Clc of the liquid crystal display panel 110 is converted into an analog data voltage capable of expressing gray scale based on the gamma reference voltage supplied from the gamma reference voltage generator 140. Supply to the data lines DL1 to DLm.

The gate driver 130 sequentially generates scan pulses, that is, gate pulses, in response to the gate driving control signal GDC and the gate shift clock GSC supplied from the timing controller 190 to generate the gate lines GL1 to GLn. Feed the fields. The gate driver 130 determines the high level voltage and the low level voltage of the scan pulse in accordance with the gate high voltage VGH and the gate low voltage VGL supplied from the gate drive voltage generator 180, respectively.

The gamma reference voltage generator 140 receives a high potential power supply voltage VDD to generate a positive gamma reference voltage and a negative gamma reference voltage and output the same to the data driver 120.

The backlight assembly 150 is disposed on the rear surface of the liquid crystal display panel 110 and emits light by an AC voltage and a current supplied from the inverter 160 to irradiate light to each pixel of the liquid crystal display panel 110.

The inverter 160 converts the square wave signal generated therein into a triangular wave signal and compares the triangular wave signal with a DC power supply voltage (VCC) supplied from the system to generate a burst dimming signal proportional to the comparison result. . When a burst dimming signal determined according to an internal square wave signal is generated, a driving IC (not shown) for controlling the generation of AC voltage and current in the inverter 160 is supplied to the backlight assembly 150 according to the burst dimming signal. Control the generation of alternating voltage and current.

The common voltage generator 170 receives the high potential power voltage VDD to generate the common voltage Vcom and supplies the common voltage Vcom to the common electrodes of the liquid crystal cells Clc of each pixel of the liquid crystal display panel 110.

The gate driving voltage generator 180 receives the high potential power voltage VDD to generate the gate high voltage VGH and the gate low voltage VGL to supply the gate driver 130 to the gate driver 130. Here, the gate driving voltage generation unit 180 generates a gate high voltage VGH that is greater than or equal to the threshold voltage of the TFTs provided in each pixel of the liquid crystal display panel 110, and the gate low voltage that is less than or equal to the threshold voltage of the TFT. VGL). The gate high voltage VGH and the gate low voltage VGL generated in this way are used to determine the high level voltage and the low level voltage of the scan pulse generated by the gate driver 130, respectively.

The timing controller 190 supplies digital video data RGB, which is supplied from a digital video card (not shown), to the data driver 120, and also horizontal / vertical synchronization signals H and V according to the clock signal CLK. The data driving control signal DDC and the gate driving control signal GDC may be generated and supplied to the data driver 120 and the gate driver 130, respectively. The data driving control signal DDC includes a source shift clock SSC, a source start pulse SSP, a polarity control signal POL, a source output enable signal SOE, and a gate driving control signal GDC. ) Includes a gate start pulse (GSP) and a gate output enable (GOE).

On the other hand, the afterimage does not appear on the screen when the common voltage Vcom generated from the common voltage generator 170 is positioned at the center of the high and low sections of the output voltage (analog data voltage) of the data driver 120. The internal resistance component of the common voltage generator 170 is substantially changed by the surrounding high temperature environment, thereby increasing or decreasing the common voltage Vcom generated from the common voltage generator 170.

As the common voltage Vcom increases or decreases, the charging amount of the high and low sections of the analog data voltages of the liquid crystal display panel 110 divided based on the common voltage Vcom in the conventional liquid crystal display device is inconsistent. Afterimages and smudges appeared on the screen.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a liquid crystal capable of varying the level of the minimum voltage, which is the control voltage of the common voltage level supplied to the liquid crystal display panel, according to the ambient temperature. A display element and its driving method are provided.

Disclosure of Invention An object of the present invention is to provide a liquid crystal display device and a method of driving the same, by adjusting a common voltage level in proportion to a minimum threshold voltage level that varies with ambient temperature, thereby compensating for a common voltage changed by an ambient temperature environment. To provide.

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal display device and a driving method thereof capable of preventing generation of afterimages and smudges on a screen by compensating for a common voltage changed by an ambient temperature environment.

The present invention for achieving the above object is a liquid crystal display panel in which a common electrode is formed in the liquid crystal cell of each pixel; Minimum voltage generation means generated by varying a minimum voltage as a reference for controlling a common voltage level according to a temperature change around the liquid crystal display panel; Common voltage adjusting means for adjusting the common voltage level according to the minimum voltage level generated by the minimum voltage generation means; And common voltage generating means for supplying a common voltage having a level controlled by the common voltage adjusting means to the common electrode.

According to an exemplary embodiment of the present invention, a common voltage is supplied to a common electrode formed in a liquid crystal cell of each pixel of a liquid crystal display panel. Generating; Varying a variable resistance value which is a determination standard of a common voltage level according to the generated minimum voltage level; And supplying a common voltage having a level varying in proportion to the variable resistance value to the common electrode.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is a configuration diagram of a liquid crystal display device according to an exemplary embodiment of the present invention.

Referring to FIG. 3, the liquid crystal display device 200 according to the present invention may include the liquid crystal display panel 110, the data driver 120, the gate driver 130, and the gamma reference voltage generator 140 as in FIG. 2. The backlight assembly 150 includes an inverter 160, a gate driving voltage generator 180, and a timing controller 190.

In addition, the liquid crystal display device 200 of the present invention includes a minimum voltage generator 210 and a minimum voltage generated by varying a minimum voltage that is a control reference of a common voltage Vcom level according to a change in ambient temperature. The common voltage control unit 220 and the high voltage supply voltage VDD are applied to adjust the common voltage Vcom level according to the minimum threshold voltage level generated by the voltage generator 210. A common voltage generator 230 for generating a common voltage Vcom having a level controlled by the unit 220 is provided.

The minimum voltage generator 210 may be generated by varying the minimum voltage, which is a control standard of the common voltage (Vcom) level, according to a change in temperature around the liquid crystal display panel 110. In the environment, the level of the minimum voltage output to the common voltage controller 220 is reduced in proportion to the increased high temperature. On the contrary, when the ambient temperature decreases, the level of the minimum voltage output to the common voltage controller 220 is reduced. Increase in proportion to the lowered temperature. A circuit configuration and a specific operation process of the minimum voltage generator 210 having such a function will be described with reference to FIG. 4.

The common voltage controller 220 adjusts the common voltage Vcom level by varying the variable resistance value of the common voltage generator 230 according to the minimum voltage level input from the minimum voltage generator 210. In particular, in the common voltage controller 220, a lookup table constructed by matching the minimum level voltage values of the multiple levels and the common voltage Vcom values of the multiple levels in one-to-one correspondence is preset. Accordingly, the common voltage controller 220 generates a common voltage Vcom value of the level set in the predetermined lookup table in correspondence with the minimum voltage value of the level input from the minimum voltage generator 210. The variable resistor value of the generator 230 is varied.

For example, when the ambient temperature is high and the high temperature environment is reached, the level of the minimum voltage generated by the minimum voltage generator 210 is lowered, so that the common voltage controller 220 refers to a predetermined lookup table to refer to the common voltage. While adjusting the level of Vcom, the variable resistance value of the common voltage generator 230 is increased so that the common voltage Vcom level increases in proportion to the lower minimum threshold voltage level. On the contrary, when the ambient temperature decreases, the level of the minimum voltage generated by the minimum voltage generator 210 increases, so that the common voltage controller 220 refers to a predetermined lookup table to determine the voltage of the common voltage Vcom. Although the level is adjusted, the variable resistance value of the common voltage generator 230 is decreased to lower the common voltage Vcom in proportion to the increased minimum threshold voltage level.

The common voltage generator 230 receives the high potential power voltage VDD to generate the common voltage Vcom and supplies the common voltage Vcom to the common electrodes of the liquid crystal cells Clc included in each pixel of the liquid crystal display panel 110. Here, the level of the common voltage Vcom is increased or decreased in proportion to the variable resistance value of the common voltage generator 230 that is varied by the common voltage adjuster 220. The circuit configuration and operation of the common voltage generator 230 having such a function will be described in more detail with reference to FIG. 5.

FIG. 4 is a circuit diagram of the minimum voltage generator of FIG. 3.

4, the minimum voltage generator 210 is a bipolar NPN type in which the base is connected to the power supply (Vs) side, the collector is connected to the high potential power supply voltage (VDD) side, and the emitter is connected to the ground side. The first thermistor Rth1 connected between the transistor TR1, the power supply Vs, and the base of the transistor TR1, and the second thermistor connected between the high potential power supply voltage VDD and the collector of the transistor TR1. Rth2 and a load resistor RL1 connected between ground and the emitter of transistor TR1, the minimum voltage being an output node located between the second thermistor Rth2 and the collector of transistor TR1. It is output through (Nout1).

The first and second thermistors Rth1 and Rth2 are semiconductors sintered by mixing oxides such as cobalt, copper, manganese, nickel, and titanium to have an appropriate resistivity and temperature coefficient. It has the characteristics that occur, the resistance value increases as the ambient temperature increases, and the resistance value decreases as the ambient temperature decreases.

For example, when the temperature around the liquid crystal display panel 110 becomes high to obtain a high temperature environment, the resistance values of the first and second thermistors Rth1 and Rth2 increase, and are supplied from the power supply Vs to the base of the transistor TR1. The voltage and current become reduced in proportion to the resistance value of the first thermistor Rth1. When the current and voltage applied to the base of the transistor TR1 are reduced in this way, the channel width of the transistor TR1 is narrowed in proportion to the reduced base voltage and the resistance value of the second thermistor Rth2 is increased. As a result, the high potential power voltage VDD across the output node Nout1 is also reduced in proportion to the resistance value of the second thermistor Rth2 which is increased, thereby reducing the level of the minimum voltage output through the output node Nout1. do.

When the temperature around the liquid crystal display panel 110 decreases, the resistance values of the first and second thermistors Rth1 and Rth2 decrease, and the voltage and current supplied from the power supply Vs to the base of the transistor TR1 decrease. It is increased in proportion to the resistance value of the reduced first thermistor Rth1. As the current and voltage applied to the base of the transistor TR1 increase, the channel width of the transistor TR1 increases in proportion to the increased base voltage and the resistance value of the second thermistor Rth2 decreases. As a result, the high potential power voltage VDD across the output node Nout1 is also increased in proportion to the resistance value of the second thermistor Rth2 which is decreased, so that the level of the minimum voltage output through the output node Nout1 is increased. Is increased.

FIG. 5 is a circuit diagram of the common voltage generator of FIG. 3.

Referring to FIG. 5, the common voltage generator 230 includes a resistor R1 and a variable resistor VR1 connected in series between a high potential power voltage VDD and a ground, and the common voltage Vcom is a resistor ( It is output through the output node Nout2 located between R1) and the variable resistor VR1.

Here, since the output node Nout2 where the common voltage Vcom is generated is located between the resistor R1 and the variable resistor VR1, the level of the common voltage Vcom is the resistance R1 and the variable resistor VR1. Is determined by the resistance values. In particular, since the resistance value of the resistor R1 is a fixed value, the level of the common voltage Vcom is varied by the resistance value of the variable resistor VR1 that is varied by the common voltage adjuster 220.

That is, when the resistance of the variable resistor VR1 is increased, the level of the common voltage Vcom output through the output node Nout2 is increased. On the contrary, when the resistance of the variable resistor VR1 is decreased, the output node Nout2 is increased. The level of the common voltage Vcom output through is reduced.

Looking at the driving method of the liquid crystal display device of the present invention having the configuration and function as described above with reference to the flowchart.

6 is a flowchart illustrating a method of driving a liquid crystal display device according to an exemplary embodiment of the present invention.

Referring to FIG. 6, first, the common voltage Vcom is supplied to the common electrode of the liquid crystal cell Clc formed in each pixel of the liquid crystal display panel 110 (S601). When the temperature is high to become a high temperature environment (S602), the minimum voltage generator 210 reduces the level of the minimum voltage output to the common voltage controller 220 in proportion to the increased high temperature (S603).

When the level of the minimum voltage is reduced, the common voltage controller 220 increases the variable resistance of the common voltage generator 230 according to the reduced minimum voltage level (S604). In this process, the common voltage adjuster 220 varies the variable resistance of the common voltage generator 230 to generate a common voltage value of a set level corresponding to the reduced minimum voltage level with reference to a predetermined lookup table. Let's do it.

The common voltage generator 230 receives the high potential power voltage VDD to generate the common voltage Vcom, but has a common level at the level determined by the variable resistance value increased by the common voltage adjuster 220. The voltage Vcom is supplied to the liquid crystal display panel 110 (S605).

On the other hand, when the ambient temperature of the liquid crystal display panel 110 is lowered in the state where the common voltage Vcom is being supplied (S606), the minimum voltage generator 210 is output to the common voltage controller 220. The level of the threshold voltage is increased in proportion to the lowered temperature (S607).

When the level of the minimum voltage is increased in this way, the common voltage controller 220 decreases the variable resistance value of the common voltage generator 230 according to the increased minimum voltage level (S608). In this process, the common voltage controller 220 may vary the variable resistance of the common voltage generator 230 to generate a common voltage value of a set level corresponding to the increased minimum threshold voltage level with reference to a predetermined lookup table. Let's do it.

The common voltage generator 230 receives the high potential power supply voltage VDD to generate the common voltage Vcom, but has a common level at the level determined by the variable resistance value reduced by the common voltage adjuster 220. The voltage Vcom is supplied to the liquid crystal display panel 110 (S609).

As described above, the present invention compensates the common voltage Vcom shifted by the surrounding high temperature environment, so that the common voltage Vcom generated from the common voltage generator 230 is always the output voltage of the data driver 120. The image is placed at the center of the high and low sections of the analog data voltage to prevent afterimages and spots on the screen.

As described above, according to the present invention, the level of the minimum voltage, which is the control voltage of the common voltage level supplied to the liquid crystal display panel, is varied according to the ambient temperature, and the common voltage level is proportional to the variable minimum voltage level. By adjusting, the common voltage changed by the ambient temperature environment can be compensated, and thus, the occurrence of afterimages and stains on the screen can be prevented.

Although the technical spirit of the present invention has been described in detail according to the above-described preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

Claims (15)

A liquid crystal display panel in which a common electrode is formed in the liquid crystal cell of each pixel; Minimum voltage generation means generated by varying a minimum voltage as a reference for controlling a common voltage level according to a temperature change around the liquid crystal display panel; Common voltage adjusting means for adjusting a common voltage level according to the minimum voltage level generated by said minimum voltage generating means; And Common voltage generating means for supplying a common voltage having a level controlled by the common voltage adjusting means to the common electrode / RTI > The minimum voltage generation means, A transistor having a base connected to the power supply side, a collector connected to the high potential power supply voltage side, and an emitter connected to the ground side; A first thermistor connected between the power supply and the base of the transistor; And A second thermistor connected between the high potential power voltage and the collector of the transistor, And an output node to which the minimum voltage is output is located between the second thermistor and the collector of the transistor. delete The method of claim 1, And when the temperature around the liquid crystal display panel increases, the resistance values of the first and second thermistors increase to decrease the level of the minimum voltage. The method of claim 1, And when the temperature around the liquid crystal display panel decreases, the resistance values of the first and second thermistors decrease to increase the level of the minimum voltage. The method of claim 1, And when the level of the minimum voltage drops, the common voltage adjusting means increases the variable resistance value of the common voltage generating means, which is a determination criterion of the common voltage level. 6. The method of claim 5, And the common voltage generating means supplies a common voltage of an increased level in proportion to the variable resistance value increased by the common voltage adjusting means to the common electrode. The method of claim 1, And when the level of the minimum voltage increases, the common voltage adjusting means reduces the variable resistance value of the common voltage generating means that is the determination standard of the common voltage level. The method of claim 7, wherein And the common voltage generating means supplies a common voltage having a reduced level in proportion to the variable resistance value reduced by the common voltage adjusting means to the common electrode. In the state in which the common voltage is supplied to the common electrode formed in the liquid crystal cell of each pixel of the liquid crystal display panel, the voltage is generated by varying the minimum threshold voltage, which is a reference for adjusting the common voltage level, according to the temperature change around the liquid crystal display panel. ; Varying a variable resistance value which is a determination standard of a common voltage level according to the generated minimum voltage level; And Supplying a common voltage having a level varying in proportion to the variable resistance value to the common electrode Including, The minimum voltage generation means for performing the minimum voltage generation step, A transistor having a base connected to the power supply side, a collector connected to the high potential power supply voltage side, and an emitter connected to the ground side; A first thermistor connected between the power supply and the base of the transistor; And Generated through a second thermistor connected between the high potential power voltage and a collector of a transistor, And an output node at which the minimum voltage is output is located between the second thermistor and the collector of the transistor. The method of claim 9, In the minimum voltage generation step, And when the temperature around the liquid crystal display panel increases, the resistance value increases to decrease the level of the minimum voltage. 11. The method of claim 10, In the variable resistance value variable step, And increasing the variable resistance value according to the lowered minimum voltage level. The method of claim 11, In the common electrode supply step, And supplying a common voltage of an increased level in proportion to the increased variable resistance value to the common electrode. The method of claim 9, In the minimum voltage generation step, And when the temperature around the liquid crystal display panel decreases, the resistance value decreases to increase the level of the minimum voltage. The method of claim 13, In the variable resistance value variable step, And the variable resistance value is reduced in accordance with the increased minimum voltage level. 15. The method of claim 14, In the common electrode supply step, And supplying a common voltage having a reduced level in proportion to the reduced variable resistance value to the common electrode.

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