KR100672654B1 - Apparatus for generating Gamma reference voltage of liquid crystal display device - Google Patents

Abstract

The present invention relates to a gamma voltage generator of a liquid crystal display device that compensates for changes in grayscale and luminance according to a temperature change of a liquid crystal display panel, and includes a temperature sensor for sensing a temperature change of the liquid crystal display device. A gamma voltage compensation unit configured to store a lookup table value of gray scale gamma characteristics for each temperature and output a gamma voltage compensation signal corresponding to a temperature sensed by the temperature sensing sensor, and a gamma voltage compensation signal output from the gamma voltage compensation unit; The gamma voltage output unit outputs a gamma reference voltage to the data driver of the liquid crystal display.

Gamma voltage compensation, liquid crystal display, temperature gamma voltage compensation

Description

Apparatus for generating Gamma reference voltage of liquid crystal display device

1 is a block diagram showing a general liquid crystal display device

2 is a voltage vs. temperature curve graph of a typical liquid crystal

3 is a waveform diagram of data according to a change in a general kick-back voltage.

4A and 4B are configuration diagrams of a temperature compensating circuit of a conventional liquid crystal display device.

5 is a graph showing gray scale vs. transmission characteristics according to temperature for explaining the present invention.

6 is a configuration diagram of a gamma voltage generator of a liquid crystal display according to a first embodiment of the present invention.

7 is a block diagram of a lookup table according to a first embodiment of the present invention;

8 is a configuration diagram of a gamma voltage generator of a liquid crystal display according to a second exemplary embodiment of the present invention.

FIG. 9 is a circuit diagram illustrating a specific thermal resistor and a gamma reference voltage generator of the first embodiment of FIG. 8.

FIG. 10 is a circuit diagram illustrating the detailed thermal resistor and gamma reference voltage generator of the second exemplary embodiment of FIG. 8.

Explanation of symbols for the main parts of the drawings

11 temperature sensor 12 gamma voltage compensation unit

12a: Micom 12b: lookup table

13: gamma voltage output unit 14, 23: data driver

21: thermal register 22: gamma reference 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 gamma voltage generating device of a liquid crystal display device that compensates for changes in grayscale and luminance according to temperature changes of a liquid crystal display panel.

In general, a liquid crystal display device is a device for displaying an image by adjusting the light transmittance of the liquid crystal in accordance with an image signal, and when the light is irradiated to the liquid crystal exhibiting polarization characteristics in accordance with the voltage applied to the pixel electrode It is a device that can express an image by adjusting the amount of light that passes according to the alignment state of.

In such a liquid crystal display, a gamma characteristic in which the gray level of an image does not change linearly but varies linearly according to the voltage level of an image signal is displayed. This is due to the fact that the light transmittance of the liquid crystal does not change linearly with the voltage level of the image signal, and the gray scale of the image does not change linearly with the light transmittance of the liquid crystal.

Therefore, the gamma correction voltages are used to change the intervals between voltage levels of the image signal differently in order to prevent the image from deteriorating due to the gamma characteristic. In other words, the liquid crystal display corrects the gamma characteristic by adding a gamma correction voltage that is preset to have a different level according to the voltage level of the image signal as an offset voltage to the voltage level of the image signal.

1 is a block diagram illustrating a general liquid crystal display device.

As shown in FIG. 1, a configuration of a liquid crystal display for correcting gamma characteristics includes a plurality of gate lines GL1 to GLm arranged in a direction perpendicular to each other to define a liquid crystal cell in a matrix form. An image display unit 2 having data lines DL1 to DLn, a gate driver 4 for driving gate lines GL1 to GLm of the image display unit 2, and the image display unit 2 And a gamma voltage generator 8 for supplying a gamma voltage to the data driver 6 and a data driver 6 for driving the data lines DL1 to DLn.

The image display unit 2 includes liquid crystal cells arranged in a matrix, a plurality of gate lines GL1 to GLm and data lines DL1 to DLn, pixel electrodes formed in the liquid crystal cell regions, And a plurality of thin film transistors formed at the intersections of the gate lines and the data lines to apply the data signals of the data lines to the pixel electrodes according to the signals of the gate lines.

The gate driver 4 sequentially supplies a gate signal to the gate lines GL1 to GLm to turn on the thin film transistor connected to the corresponding gate line.

The data driver 6 supplies an image signal for one horizontal line to the data lines DL1 to DLn in synchronization with the respective gate signals, and the gamma voltage generator 8 supplies the voltage level of the image signal. Accordingly, a DC voltage preset to have different levels is supplied to the data driver 6 as a gamma voltage. Accordingly, the data driver 6 adds a gamma voltage input from the gamma voltage generator 8 to the image signal and supplies the same to the data lines, thereby correcting the gamma characteristic of the liquid crystal display.

In addition, as described above, the liquid crystal display is an apparatus capable of expressing an image by adjusting the amount of light that passes according to the alignment state of the liquid crystal due to voltage application, and includes an upper substrate having a common electrode and a lower substrate having a pixel electrode formed thereon. The liquid crystal layer is formed in between. Therefore, in the liquid crystal used in the liquid crystal display, the liquid crystal layer is interposed between the pixel electrode and the common electrode to form a capacitor Clc. As described above, the liquid crystal layer has a capacitor component, and the common voltage of the DC voltage is applied to the common electrode.

However, as the temperature changes, the characteristics of the liquid crystal change, and as the temperature increases, the capacitor component of the liquid crystal decreases, leading to an increase in kick-back voltage. In this case, the common voltage applied to the common electrode should be varied to compensate for the changed kick-back voltage. However, since the common voltage of DC is applied to the common electrode from the outside, it is difficult to compensate the kick-back voltage and therefore flicker. ) Occurs.

Therefore, in the related art, the kick-back voltage is compensated by changing the common voltage level externally according to the change amount of the gamma curve of the liquid crystal due to temperature change.

This will be described in detail as follows.

2 is a voltage versus temperature curve of a typical liquid crystal, and FIG. 3 is a waveform diagram of data according to a change in kick-back voltage.

4A and 4B are schematic diagrams of a temperature compensating circuit of a conventional liquid crystal display.

The voltage versus temperature curve of the liquid crystal is influenced by the external temperature, as shown in FIG. That is, the capacitor value of the liquid crystal is changed.

Here, the kick-back voltage Vk-b voltage is defined as follows.

 Vk-b = {ΔVg × Cgd} over {Cgd + Clc + Cst}

This change in kick-back voltage, as shown in FIG. 3, results in a reduction of the data constant voltage relative to the common voltage applied to the liquid crystal. That is, the compensation should be made as much as the shaded area ΔV '.

Therefore, the common voltage is compensated according to the temperature by including a temperature compensation circuit as shown in FIGS. 4A and 4B.

That is, as shown in FIG. 4A, the resistors R1 and R2 and the first thermal resistor Rt1 are connected in series between the constant voltage V1 and the ground terminal GND, and the resistors R1 and R2 are connected to each other in series. The divided voltage is output as the common voltage Vcom. Here, the first thermal resistor Rt1 is a resistor whose resistance value decreases when the temperature rises.

In addition, as shown in FIG. 4B, a second thermal resistor Rt2 and resistors R1 and R2 are connected in series between the constant voltage V1 and the ground terminal GND, and the resistors R1 and R2 are connected to each other in series. The divided voltage is output as the common voltage Vcom. Here, the second thermal resistor Rt1 is a resistor whose resistance increases as the temperature increases.

Accordingly, the kick-back voltage is compensated for by setting the common voltage Vcom at the initial room temperature and changing the common voltage value by the resistance string method by the difference in the gamma curve of the liquid crystal with respect to the temperature change.

That is, when the temperature rises, the resistance value of the first thermal resistor Rt1 decreases, and the second thermal resistor Rt2 increases, so that the common voltage Vcom decreases.

At this time, the output common voltage Vcom is as follows.

Vcom = {((R1 + R2)} over {R1 + R2 + Rt1} × V1 or

 Vcom = {R2 + Rt1} over {R1 + R2 + rt1} × V1

In the related art, the kick-back voltage is compensated for by changing the common voltage value according to the temperature change, thereby preventing the flicker phenomenon.

However, the following problem occurs in the temperature compensation method of the conventional liquid crystal display device as described above.

In general, the viscosity of the liquid crystal changes with temperature, and when the viscosity of the liquid crystal changes, the response time of the liquid crystal changes. In other words, at low temperatures, the response time of the liquid crystal is slow, and at high temperatures, the response time of the liquid crystal is faster.                         

Therefore, even when the common voltage is compensated for according to the temperature change, a tail phenomenon occurs at a low temperature, and a blurring phenomenon occurs that the screen is blurred at a high temperature.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. A gamma voltage generator of a liquid crystal display device capable of optimizing a gamma reference voltage according to a temperature change by detecting a temperature change of a liquid crystal display panel and compensating the gamma reference voltage by the changed temperature. The purpose is to provide.

The gamma voltage generator of the liquid crystal display according to the present invention for achieving the above object, the temperature sensing sensor for detecting a temperature change of the liquid crystal display, and the look-up table value of gray scale gamma characteristics for each temperature and store the A gamma voltage compensator for outputting a gamma voltage compensation signal corresponding to a temperature sensed by a temperature sensor, and a gamma reference voltage to a data driver of the liquid crystal display according to the gamma voltage compensation signal output from the gamma voltage compensator It is characterized by having a gamma voltage output unit.

In addition, the gamma voltage generator of the liquid crystal display device according to the present invention for achieving the above object, the thermal resistor is variable according to the temperature of the liquid crystal display device, and the plurality of divided resistors between the constant voltage and the ground terminal; It is further characterized by having a gamma reference voltage generator which is connected in series and outputs a gamma reference voltage to the data driver according to the divided resistance ratio of the node points of the divided resistors according to the resistance value of the thermal resistor.

The gamma voltage generator of the liquid crystal display according to the present invention having the above characteristics will be described in more detail with reference to the accompanying drawings.

5 is a graph showing gray scale vs. transmission characteristics according to temperature for explaining the present invention.

As described in the related art, the liquid crystal display has a change in the gamma curve due to temperature change due to liquid crystal characteristics, and thus a gray scale change occurs at high temperature, low temperature, and room temperature, thereby affecting the image quality of the liquid crystal display.

That is, as shown in FIG. 5, the temperature of 25 ° C has a gamma value of 2.18, the temperature of 0 ° C has a gamma value of 2.08, and the temperature of -25 ° C has a gamma value of 1.5.

6 is a configuration diagram of a gamma voltage generator of a liquid crystal display according to a first embodiment of the present invention, and FIG. 7 is a configuration diagram of a lookup table according to a first embodiment of the present invention.

As shown in FIG. 6, the gamma voltage generator of the liquid crystal display according to the first embodiment of the present invention includes a temperature sensor 11 for detecting a temperature change of the liquid crystal display, and a gray scale according to temperature. A gamma voltage compensator 12 for storing a lookup table value of each gamma characteristic and outputting a gamma voltage compensation signal corresponding to a temperature sensed by the temperature sensor 11 and outputting the gamma voltage compensator 12 The gamma voltage output unit 13 outputs a gamma reference voltage to the data driver 14 of the liquid crystal display according to the gamma voltage compensation signal.

Here, the gamma voltage compensator 12 determines the temperature of the liquid crystal display by determining the signal input from the temperature sensor 11, and loads a lookup table corresponding to the determined temperature to output a compensation signal. And a look-up table part 12b for storing the compensation value of the gamma characteristic for each gray scale according to the temperature and providing it to the micom 12a.

Although not shown in the drawing, the gamma voltage output unit 13 is composed of a plurality of divided resistor rows, and the plurality of divided resistors are connected in series between the constant voltage Vdd and the ground terminal GND. The voltage level is configured to be determined according to the divided resistance ratio of the node point of the divided resistors. Among the voltage levels, one of a plurality of voltage levels is provided to the data driver according to the compensation signal of the gamma voltage floating part 12.

The lookup table 12b of the gamma voltage compensator 12 is configured as shown in FIG. 7.

FIG. 7 illustrates a lookup table when the temperature of the liquid crystal display is 0 ° C. from the temperature sensor 11. When the system supplies a data signal to the liquid crystal display, the gray level is based on the room temperature (25 ° C.). It is determined and entered. Thus, when a temperature lower than room temperature is detected, the system is configured to adjust the input gray level upward, and when a voltage higher than room temperature is detected, the system adjusts the input gray level. That is, assuming that the gray level is input to 23, the level is increased by 6 at 0 ° C to compensate for the gray level corresponding to 29.

The operation of the gamma voltage generator of the liquid crystal display according to the first embodiment of the present invention configured as described above is as follows.

The temperature sensor 11 detects and outputs an ambient temperature of the liquid crystal display. Then, the microcomputer 12a of the gamma voltage compensator 12 receives this to determine a temperature, reads a lookup table corresponding to the determined temperature, and outputs a compensation signal.

That is, as shown in FIG. 7, when the temperature sensor 11 determines that the ambient temperature of the liquid crystal display is 0 ° C., the lookup table corresponding to 0 ° C. is read. In addition, if the gray level is input to 23 in the system, the gamma voltage compensator 12 increases the level by 6 and outputs a compensation signal at a gray level corresponding to 29.

 Then, the gamma voltage output unit 13 outputs a gamma reference voltage corresponding to level 29 to the data driver 14.

By this method, even if the temperature changes, the gamma curve has an appropriate curve, and has the same gray scale characteristics as at room temperature.

On the other hand, it is possible to provide an appropriate gamma voltage without using the same lookup table as in the first embodiment of the present invention.

8 is a configuration diagram of a gamma voltage generator of a liquid crystal display according to a second exemplary embodiment of the present invention, and FIG. 9 is a circuit diagram illustrating a specific thermal resistor and gamma reference voltage generator of the first embodiment of FIG. 8. FIG. 10 is a circuit diagram illustrating a specific thermal register and gamma reference voltage generator of the second exemplary embodiment of FIG. 8.

As shown in FIG. 8, the gamma voltage generator of the liquid crystal display according to the second embodiment of the present invention includes a thermal resistor 21 and a constant voltage Vdd, the resistance of which varies depending on the temperature of the liquid crystal display. The plurality of voltage divider resistors are connected in series between a ground terminal GND to transmit a gamma reference voltage to the data driver 23 according to the voltage divider resistance ratio of the node point of each voltage divider resistor in accordance with the resistance value of the thermal resistor 21. It comprises a gamma reference voltage generator 22 for outputting.

Here, the thermal resistor 21 and the gamma reference voltage generator 22 will be described in more detail as follows.

That is, the resistance value may decrease when the temperature of the thermal resistor 21 increases, and conversely, the resistance value may increase when the temperature increases.

Therefore, in the case of using the thermal resistor 21 in which the resistance value also increases when the temperature rises, as shown in FIG. 9, the first divided voltage connected in series between the constant voltage Vdd and the first ground terminal GND1. The gamma reference voltage generator 22 is provided with resistors R1 through R9 and second voltage dividers R10 through R18 connected in series between the constant voltage Vdd and the second ground terminal GND2. Configure. The thermal resistor 21 is connected between the first and second voltage divider resistors R1 to R18 and the constant voltage Vdd terminal.

In addition, in the case of using the thermal resistor 21 in which the resistance value decreases when the temperature rises, as shown in FIG. 10, the first divided voltage connected in series between the constant voltage Vdd and the first ground terminal GND1. The gamma reference voltage generator 22 is provided with resistors R1 through R9 and second voltage dividers R10 through R18 connected in series between the constant voltage Vdd and the second ground terminal GND2. Configure. And a thermal resistor 21 between the first divided resistors R1 to R9 and the first ground terminal GND1, and between the second divided resistors R10 to R18 and the second ground terminal GND2, respectively. ).

Also in the gamma voltage generator of the liquid crystal display according to the second embodiment of the present invention described above, since the resistance value of the thermal resistor is changed according to the temperature change, an appropriate gamma voltage is generated according to the temperature change. The proper gray scale of is maintained.

In the liquid crystal display gamma voltage generator according to the present invention as described above has the following effects.

In general, a liquid crystal display generates a change in gray scale and luminance according to a change in ambient temperature. Therefore, in the present invention, since the gamma reference voltage is compensated according to the temperature change by using a temperature sensor or a thermal resistor that senses the ambient temperature of the liquid crystal display, it is possible to maintain an appropriate gray scale and luminance even at high or low temperatures.

Claims (7)

A temperature sensor for detecting a temperature change of the liquid crystal display device; A gamma voltage compensator for storing a lookup table value of gray scale gamma characteristics for each temperature and outputting a gamma voltage compensation signal corresponding to a temperature sensed by the temperature sensor; And a gamma voltage output unit configured to output a gamma reference voltage to a data driver of the liquid crystal display according to the gamma voltage compensation signal output from the gamma voltage compensation unit. The method of claim 1, The gamma voltage compensator may include: a microcomputer that determines a temperature of the liquid crystal display by determining a signal input from the temperature sensor, calls a lookup table corresponding to the determined temperature, and outputs a compensation signal; And a lookup table for storing the compensation value of the gray scale gamma characteristic for each temperature and providing the compensation to the microcomputer. A thermal resistor whose resistance varies depending on the temperature of the liquid crystal display, The plurality of voltage divider resistors are connected in series between a constant voltage and a ground terminal to output a gamma reference voltage to the data driver according to the voltage divider ratio of the node point of each voltage divider according to the resistance value of the thermal resistor. Gamma voltage generator of the liquid crystal display device characterized in that it comprises a. The method of claim 3, wherein The gamma reference voltage generator includes a first voltage divider connected in series between the constant voltage Vdd and the first ground terminal GND1, and a second voltage connected in series between the constant voltage and the second ground terminal GND2. With voltage divider resistors, And the thermal resistor is connected between the first and second voltage divider resistors and the constant voltage (Vdd) terminal. The method of claim 4, wherein The thermal resistor is a gamma voltage generator of the liquid crystal display device, characterized in that the resistance value increases as the temperature rises. The method of claim 3, wherein The gamma reference voltage generator includes a first voltage divider connected in series between the constant voltage Vdd and the first ground terminal GND1, and a second voltage connected in series between the constant voltage and the second ground terminal GND2. With voltage divider resistors, The thermal resistor is connected between the first divided resistors and the first ground terminal GND1 and between the second divided resistors and the second ground terminal GND2, respectively. Device. The method of claim 6, The thermal resistor is a gamma voltage generator of the liquid crystal display, characterized in that the resistance value decreases as the temperature rises.

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