KR20040100559A - Gamma reference voltage generation of Liquid Crystal Display Device - Google Patents

Abstract

PURPOSE: A gamma reference voltage circuit of a liquid display device is provided to minimize the luminance variance between liquid crystal display panels by controlling the Luminance in the black level and the white level due to the change of the pretilt angle. CONSTITUTION: A gamma reference voltage circuit of a liquid display device includes a negative polarity voltage output unit(700) and a positive polarity voltage output unit(701). The negative polarity voltage output unit is connected between the ground and the negative voltage power in serial. The negative polarity voltage output unit is provided with a plurality of resistors and at least one variable resistor for outputting a plurality of negative polarity gray level voltages by dividing the gray level voltage supplied from the negative voltage power. The positive polarity voltage output unit is connected between the ground and the positive polarity voltage power. The positive polarity voltage output unit is provided with a plurality of resistors and at least one variable resistor for outputting a plurality of positive polarity gray level voltage by dividing the positive polarity voltage supplied from the positive polarity voltage power.

Description

Gamma reference voltage generation of Liquid Crystal Display Device

The present invention relates to a gamma reference voltage circuit of a liquid crystal display device, and more particularly, to a gamma reference voltage circuit of a liquid crystal display device capable of reducing luminance variations in a white level and a black level.

Such a liquid crystal display may be classified into a liquid crystal panel displaying a video signal and a driving circuit applying a driving signal to the liquid crystal panel from the outside.

Although not shown in the drawing, the liquid crystal panel is a display device in which liquid crystal is injected between a first substrate (glass substrate) and a second substrate (glass substrate) bonded to each other with a predetermined space, and one of the two glass substrates A plurality of gate lines arranged at regular intervals, a plurality of data lines arranged at regular intervals in a direction perpendicular to the gate line, and formed in each pixel region in a matrix form defined by the gate lines and the data lines A plurality of thin film transistors are formed at portions where the gate lines and the data lines cross each other.

Therefore, when the turn-on signal is sequentially applied to the gate line, an image is displayed because the data signal is applied to the pixel electrode of the corresponding line.

According to the type of liquid crystal used in the liquid crystal display, there are various methods such as TN (Twisted Nematic) mode, Optical Compensated Birefringency (OCB) mode, and Polymer Dispersed Liquid Crystal (PDLC) mode. It is a trend that is being used a lot because of the fast speed, has the characteristics of a wide viewing angle.

Hereinafter, a liquid crystal display device having a general OCB mode including a liquid crystal panel configured as described above and a data driving circuit for applying data to the liquid crystal panel will be described with reference to the accompanying drawings.

1 is a block diagram of a driving circuit of a general liquid crystal display device.

That is, as described above, the liquid crystal display device includes a liquid crystal panel 21 having a plurality of gate lines G and data lines D arranged in a direction perpendicular to each other and having a matrix-type pixel region, and the liquid crystal panel ( 21 is divided into a driving circuit unit 22 for supplying a driving signal and a data signal, and a backlight 28 for providing a constant light source to the liquid crystal panel 21.

The driving circuit unit 22 may include a gate driver extending the data driver 21b for inputting a data signal to each data line of the liquid crystal display panel 21 and the gate lines G of the liquid crystal panel 21. A gate driver 21a for applying a signal, display data R, G, and B input from the drive system 27 of the liquid crystal panel, vertical and horizontal synchronization signals V _sync and H _sync , a clock signal DCLK, and the like. A timing for receiving the control signal DTEN and formatting each display data, clock, and control signal at a timing suitable for each data driver 21b and the gate driver 21a of the liquid crystal panel 21 to reproduce a screen. A controller 23, a power supply unit 24 for supplying a voltage required for the liquid crystal panel 21 and each unit, and a digital data input from the data driver 21b by receiving power from the power supply unit 24. To the gamma reference voltage unit 25 for supplying a reference voltage required to convert analog data, wherein said using the voltage output from power supply 24 is a constant voltage that is used for a liquid crystal panel (21) (V _dd), the gate DC / DC converter 26 for outputting a high voltage V _GH , a gate low voltage V _GL , a reference voltage V _ref , a common voltage V _com , and an inverter for driving the backlight 28. It is comprised with 29.

The operation of the driving circuit of the general liquid crystal display device configured as described above is as follows.

That is, the timing controller 23 controls the display data R, G, and B inputted from the driving system 27 of the liquid crystal panel, the vertical and horizontal synchronization signals V _sync and H _sync , and the clock signal DCLK. Since the data driver 21b and the gate driver 21a of the liquid crystal panel 21 provide the display data, the clock, and the control signal at a timing suitable for reproducing the screen, the gate driver ( 21a applies a gate driving pulse to each gate line G of the liquid crystal panel 21, and in synchronization with the data driver 21b, a data signal is applied to each data line D of the liquid crystal panel 21. Display the input video signal.

The gamma reference voltage unit 25 receives R, G, and B data signals from a controller (not shown), and generates a gray voltage suitable for a digital code value according to the number of bits of the R, G, and B data signals. It is generated and output to the data driver.

Here, the gamma reference voltage circuit configured in the gamma reference voltage unit 25 will be described in more detail as follows.

2 is a block diagram of a conventional gamma reference voltage circuit.

In the conventional gamma reference voltage circuit, as shown in FIG. 2, a negative voltage power supply (-Vdd) providing a ground terminal and a negative voltage is connected in series between the ground terminal and the negative voltage power supply (-Vdd). A negative voltage output unit 200 including a plurality of series resistors connected to each other to output a plurality of negative gray voltages (-V0 to -V8) by dividing the negative voltage supplied from the negative power supply voltage (-Vdd); )Wow; Positive voltage supply (+ Vdd) connected in series between the positive voltage supply (+ Vdd) and the ground terminal and the positive voltage supply (+ Vdd) for providing a ground terminal and a positive voltage voltage supplied from the positive voltage supply (+ Vdd) A positive voltage output unit 201 comprising a plurality of series resistors for dividing the polar voltages to output a plurality of positive gray voltages (+ V0 to + V8); The negative and positive gray voltages (−V0 to -V8, + V0 to + V9) output from the negative and positive voltage output units 200 and 201 are received. A voltage selector 202 for switching and outputting any one of V0 to -V8 and + V0 to + V9; The amplification unit 203 is configured to receive and amplify the negative gray voltages (-V0 to -V8) or the positive gray voltages (+ V0 to + V8) output from the voltage selector 202 and output the amplified signal.

The operation of the gamma reference voltage circuit configured as described above will be described in detail as follows.

When the negative voltage supplied from the negative voltage power supply (-Vdd) is applied to the plurality of series resistors, the plurality of resistors divide the applied negative voltage to obtain the plurality of negative gray voltages (-V0 to -V8). Output

At the same time, when a positive voltage supplied from a positive voltage power supply (+ Vdd) is applied to a plurality of series resistors, the plurality of resistors divide the applied positive voltage to generate a plurality of positive gray voltages (+ V0 to + Outputs V8).

That is, the negative voltage output unit 200 outputs the negative gray voltage, and the positive voltage output unit 201 outputs the positive gray voltage.

Then, the negative and positive gray voltages (-V0 to -V8, + V0 to + V8) output from the negative and positive voltage output units 200 and 201 are input to the voltage selector 202, One of the input negative and positive gray voltages (-V0 to -V8, + V0 to + V8) is selected and output by a switch provided in the voltage selector 202.

Thereafter, the negative gray voltages (-V0 to -V8) or the positive gray voltages (+ V0 to + V8) output from the voltage selector 202 are input to the amplifier 203 to remove noise and output the same. And input to the data driver (21b of FIG. 1).

Then, the data driver 21b of FIG. 1 uses the input negative gray voltages (-V0 to -V8) or positive gray voltages (+ V0 to + V8) to analogize R, G, and B digital video signals. A liquid crystal driving voltage is output by converting into a video signal, and the output liquid crystal driving voltage is applied to the data line (D of FIG. 1) of the liquid crystal panel 21 of FIG. 1 every scanning.

Here, the plurality of negative gray voltages (-V0 to -V8) and the positive gray voltages (+ V0 to + V8) are expressed as the amount of light, that is, the luminance, and the negative voltage power source among the plurality of resistors ( -Vdd) or the negative gradation voltage (-V8) and the positive gradation voltage (+ V8), which are divided and output by a resistor connected directly to the positive voltage power supply (+ Vdd), are the highest gradation levels, and therefore the darkest black level Since the negative gray voltage (-V0) and the positive gray voltage (+ V0) divided and output by the resistor connected directly to the ground terminal are the lowest gray level, the brightest white level is represented. The plurality of resistors configured between the black level and the white level resistors represent gray levels, which are intermediate levels between the black level and the white level.

However, the gamma reference voltage circuit of the conventional liquid crystal display device has the following problems.

First, the OCB mode liquid crystal display device exhibits higher luminance (transmittance) characteristics than the commonly used TN mode liquid crystal display device, but the magnitude of the luminance due to the gray scale voltage at the white level is sharper than that of the TN mode liquid crystal display device. There is a decreasing problem.

3 is a graph showing voltage versus luminance in the conventional OCB mode and TN mode.

That is, as shown in FIG. 3, the OCB mode exhibits a characteristic in which the inclination of luminance rapidly increases even with a small voltage change in the white level 300, as compared with the TN mode. During mass production of the device, the luminance deviation between the liquid crystal panels of each liquid crystal display device is intensified.

Second, there is a problem that the variation in luminance in the white and black level is intensified by the change in the external temperature.

FIG. 4A is a graph illustrating changes in external temperature and thus transmittance in the OCB mode, and FIG. 4B is an enlarged graph of an area of the black level 401 of FIG. 4A.

That is, as shown in FIGS. 4A and 4B, in the OCB mode, luminance deviation in the white level 400 and the black level 401 increases according to the external temperature, and thus, in mass production of the liquid crystal panel, The luminance deviation between the liquid crystal panels is intensified.

Third, generally, in the process of the liquid crystal panel, the cell gap of the liquid crystal panel, that is, the gap between the first substrate and the second substrate and the liquid crystal molecules of the liquid crystal layer injected between the first substrate and the second substrate and the first substrate And a deviation in the angle (pretilt angle) between the second substrate and the second substrate, the luminance deviation in the gray level and the black level is increased by the deviation.

FIG. 5A is a graph illustrating a change in cell gap and a change in luminance of the OCB mode, and FIG. 5B is an enlarged graph of the black level region of FIG. 5A.

6A is a graph showing the pretilt angle of the liquid crystal and the luminance change in the OCB mode according to the present invention. FIG. 6B is an enlarged graph of the black level region of FIG. 6A.

That is, variations in luminance at the white levels 500 and 600 and the black levels 501 and 601 are caused by variations in the cell gap and the pretilt angle of the liquid crystal. The luminance deviation is intensified.

SUMMARY OF THE INVENTION The present invention has been made to solve such a conventional problem, and by configuring a variable resistor in the positive voltage output portion and the negative voltage output portion of the gamma reference voltage circuit of the liquid crystal display device, the luminance deviation in the white level and the black level. It is an object of the present invention to provide a gamma reference voltage circuit of a liquid crystal display device which can reduce the voltage.

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

2 is a block diagram of a conventional gamma reference voltage circuit.

3 is a graph illustrating a change in luminance according to a gray voltage in TN and OCB modes.

4A and 4B are graphs illustrating a change in luminance according to external temperature in OCB mode.

5A and 5B are graphs showing a change in luminance according to a cell gap in OCB mode

6A and 6B are graphs illustrating changes in luminance according to pretilt angles of liquid crystal molecules in OCB mode.

7 is a block diagram of a gamma reference voltage circuit according to an exemplary embodiment of the present invention.

* Explanation of symbols on the main parts of the drawings

700: negative voltage output unit 701: positive voltage output unit

702: voltage selector 703: amplifier

704: first variable resistor 705: second variable resistor

706: third variable resistor 707: fourth variable resistor

The gamma reference voltage circuit of the liquid crystal display according to the present invention for achieving the above object is a data driver for outputting an analog video signal to the data line of the liquid crystal panel and the data driver converts the digital video signal into the analog video signal A gamma reference voltage section for providing a gray scale voltage required to supply a plurality of gray scale voltages, the plurality of negative voltages being connected in series between a ground terminal and a negative voltage power supply to divide a negative voltage supplied by the negative voltage power supply to output a plurality of negative gray voltages. A negative voltage output unit comprising three resistors and at least one variable resistor; A positive voltage comprising a plurality of resistors and at least one variable resistor connected in series between the ground terminal and the positive voltage power supply to divide the positive voltage supplied by the positive voltage power to output a plurality of positive grayscale voltages. It is characterized by including an output unit.

Here, in the negative voltage output unit, one side of the variable resistor is connected in series to the ground terminal, the other side is characterized in that connected in series to a plurality of resistors.

In the negative voltage output unit, one side of the variable resistor is connected in series with a negative voltage power supply, and the other side is connected in series to a plurality of resistors.

In the positive voltage output unit, one side of the variable resistor is connected in series with a ground terminal, and the other side is connected in series with a plurality of resistors.

In the positive voltage output unit, one side of the variable resistor is connected in series with a positive voltage power supply, and the other side is connected in series to a plurality of resistors.

Hereinafter, the gamma reference voltage circuit of the liquid crystal display according to the present invention having such a feature will be described in detail with reference to the accompanying drawings.

7 is a block diagram of a gamma reference voltage circuit of a liquid crystal display according to an exemplary embodiment of the present invention.

The gamma reference voltage circuit of the liquid crystal display according to the present invention includes a negative voltage output unit 700 for outputting negative gray voltages (-V0 to -V8), as shown in FIG. A positive voltage output unit 701 for outputting positive gray voltages (+ V0 to + V8); The negative polarity receives the negative gray voltages (-V0 to -V8) and the positive gray voltages (+ V0 to + V8) output from the negative voltage output unit 700 and the positive voltage output unit 701. A voltage selector 702 which selects and outputs any one of gray voltages (-V0 to -V8) and positive gray voltages (+ V0 to + V8); The amplification unit 703 amplifies and outputs the negative gray voltages (-V0 to -V8) or the positive gray voltages (+ V0 to + V8) selected and output by the voltage selector 702.

Here, the negative voltage output unit 700 is connected in series between a negative voltage power supply (-Vdd) for generating and outputting a ground terminal and a negative voltage, and the ground terminal and the negative voltage power supply (-Vdd). And a plurality of resistors and first and second variable resistors 704 and 705 for dividing the negative voltage output from the negative voltage power supply (-Vdd) to output a plurality of negative gray voltages (-V0 to -V8). The positive voltage output unit 701 includes a ground terminal and a positive voltage power supply (+ Vdd) for generating and outputting a positive voltage, and between the ground terminal and the positive voltage power supply (+ Vdd). A plurality of resistors and third and fourth variable resistors 706 and 707 connected in series to divide a positive voltage of the positive voltage power supply (+ Vdd) to output a plurality of positive gray scale voltages (+ V0 to + V8); )

In the negative voltage output unit 700, one side of the first variable resistor 704 is connected in series to a negative voltage power source (-Vdd), and the other side is connected to a plurality of resistors. One side of the second variable resistor 705 is connected in series with a ground terminal, and the other side is connected in series with a plurality of resistors.

In the positive voltage output unit 701, one side of the third variable resistor 706 is connected in series with a positive voltage power supply (+ Vdd), and the other side is connected in series with a plurality of resistors. One side of the fourth variable resistor 607 is connected in series with a ground terminal, and the other side thereof is connected in series with a plurality of resistors.

The operation of the gamma reference voltage circuit of the liquid crystal display device configured as described above will be described in detail as follows.

First, in the negative voltage output unit 700, when the negative voltage power supply (-Vdd) generates and outputs a negative voltage, the negative voltage may include a plurality of resistors and first and second variable resistors 704 and 705. ) And the plurality of resistors and the first and second variable resistors 704 and 705 divide the applied negative voltage to output a plurality of negative gray voltages (-V0 to -V8).

More specifically, since the plurality of resistors and the first and second variable resistors 704 and 705 are connected in series between the negative voltage power source (-Vdd) and the ground terminal, the resistor terminals (resistance and The negative voltage applied to the first and second variable resistors gradually increases as the voltage drop increases through the first variable resistor 704 to the second variable resistor 705, so that one side of the negative voltage power supply ( The first variable resistor 704 directly connected in series with -Vdd outputs the highest negative gray voltage (-V8), and the second variable resistor 705 directly connected in series with the ground terminal has the lowest negative value. The polarity gray voltage (-V0) is output.

Accordingly, the plurality of resistors connected in series between the other side of the first variable resistor 704 and the other side of the second variable resistor 705 may have the highest negative gray level voltage (−) output from the first variable resistor 704. A plurality of negative gray voltages (-V1 to -V7) between V8) and the lowest negative gray voltage (-V0) output from the second variable resistor 705 are output.

At the same time, in the positive voltage output unit 701, when the positive voltage power supply (+ Vdd) generates and outputs the positive voltage, the positive voltage is divided into a plurality of resistors and the third and fourth variable resistors 706, 707, and the plurality of resistors and the third and fourth variable resistors 706 and 707 divide the applied positive voltage to output a plurality of positive gray voltages (+ V0 to + V8). .

More specifically, since the plurality of resistors and the third and fourth variable resistors 706 and 707 are connected in series between the positive voltage power source (+ Vdd) and the ground terminal, the resistor terminals (resistance and The positive voltage applied to the third and fourth variable resistors is gradually increased as the voltage drop increases toward the fourth variable resistor 707 via the third variable resistor 706, so that one side of the positive voltage source ( The third variable resistor 706 directly connected in series with + Vdd outputs the highest positive gray level voltage (+ V8), and the second variable resistor 707 directly connected in series with the ground terminal has the lowest positive voltage. The polarity gray voltage (+ V0) is output.

Accordingly, the plurality of resistors connected in series between the other side of the third variable resistor 706 and the other side of the fourth variable resistor 707 may have the highest negative gray level voltage (+) output from the third variable resistor 706. The plurality of negative gray voltages (+ V1 to + V7) between V8) and the lowest negative gray voltage (+ V0) output from the fourth variable resistor 707 are output.

Thereafter, the plurality of negative gray voltages (-V0 to -V8) and the positive gray voltages (+ V0 to + V8) output from the negative output unit and the positive output units 700 and 701 may be voltage selection units. The voltage selector selects and outputs one of the two types of gray voltages (a negative gray voltage and a positive gray voltage).

Then, the negative gray voltages (-V0 to -V8) or the positive gray voltages (+ V0 to + V8) are input to the amplifying unit and amplified to remove noise and more stably output.

The plurality of negative gray voltages (-V0 to -V8) and the positive gray voltages (+ V0 to + V8) (hereinafter referred to as gray voltages) output as described above are expressed as an amount of light, that is, luminance. Since the first and third variable resistors 704 and 706 output the highest gray voltages (-V8 and + V8), they represent the darkest black levels and the second and fourth variable resistors 705 and 707. Outputs the lowest gray voltages (-V0, + V0), resulting in the brightest white level.

The plurality of resistors connected in series between the first variable resistor 704 and the second variable resistor 705 and the plurality of resistors connected in series between the third variable resistor 706 and the fourth variable resistor 707. Represents the gray level, which is the intermediate value between the black level and the white level.

As described above, in the OCB mode, the luminance deviation in the black level and the white level is intensified by the change in the luminance characteristic of the OCB, the external temperature, the cell gap, and the pretilt angle of the liquid crystal.

Accordingly, by adjusting the first and third variable resistors 704 and 706 outputting the highest gray voltages (-V8 and + V8) corresponding to the black level, the luminance at the black level shown in FIG. 4B is adjusted. Can be.

For example, as shown in FIGS. 4A and 4B, the luminance at the black level 401 of the liquid crystal panel manufactured at 30 ° C. represents 0.8, and the luminance at the black level 401 of the liquid crystal panel manufactured at 40 ° C. If the luminance is 0.4 and a luminance deviation of 0.4 occurs between the two liquid crystal panels, the first variable resistor 704 or the third variable resistor 706 of the liquid crystal panel manufactured at 40 ° C. is adjusted to decrease the luminance. The luminance may be the same as that of the luminance (0.4) of the liquid crystal panel manufactured at 30 ° C.

That is, according to the luminance characteristic graph of the liquid crystal panel manufactured at a temperature of 40 ° C., in order to decrease the brightness of the liquid crystal panel manufactured at 40 ° C. from 0.8 to 0.4, the gray scale voltage should be increased, so that the first or third The resistance values of the variable resistors 704 and 706 may be increased.

The white level is adjusted by adjusting the second or fourth variable resistors 705 and 707 that output the lowest gray voltages (-V0 and + V0) corresponding to the white level, as shown in FIGS. 4A and 4B. The luminance at 400 can be adjusted.

For example, as shown in FIGS. 4A and 4B, the luminance at the white level 400 of the liquid crystal panel manufactured at 30 ° C. is 60, and the luminance at the black level of the liquid crystal panel manufactured at 40 ° C. is 40. If a luminance deviation of 20 occurs between the two liquid crystal panels, the luminance is increased by adjusting the second or fourth variable resistors 705 and 707 of the liquid crystal panel manufactured at 40 ° C., thereby increasing the luminance. The luminance may be the same as the luminance 60 of the panel.

That is, according to the luminance characteristic graph of the liquid crystal panel manufactured at a temperature of 40 ° C., in order to increase the brightness of the liquid crystal panel manufactured at 40 ° C. from 40 to 60, the gray scale voltage should be decreased, so that the second or fourth The resistance values of the variable resistors 705 and 707 may be increased.

Similarly, luminance variations at black and white levels due to variations in cell gaps and pretilt angles can also be compensated.

Although four variable resistors are used in the embodiment of the present invention, two variable resistors may be configured using one variable resistor at the black level and one variable resistor at the white level.

That is, the first and second variable resistors 704 and 705 or the third and fourth variable resistors 706 and 707 or the second and third variable resistors 705 and 706 or the first and fourth variable resistors 704. , 707).

The present invention described above is not limited to the above-described embodiment and the accompanying drawings, and it is common in the art that various substitutions, modifications, and changes can be made without departing from the technical spirit of the present invention. It will be evident to those who have knowledge of.

As described above, the gamma reference voltage circuit of the liquid crystal display according to the present invention has the following effects.

With a variable resistor to adjust the brightness change at the black level and the white level, the black level and the white level due to the characteristics of the white level in the OCB mode and the change of the external temperature, the cell gap and the pretilt angle of the liquid crystal molecules Since the luminance of the liquid crystal panel may be adjusted, the luminance variation between the liquid crystal panels according to mass production of the liquid crystal display device may be minimized.

Claims (7)

A data driver for outputting an analog video signal to a data line of a liquid crystal panel and a gamma reference voltage circuit of a liquid crystal display device for providing a gray scale voltage necessary for the data driver to convert a digital video signal into the analog video signal. A negative voltage comprising a plurality of resistors and at least one variable resistor connected in series between the ground terminal and the negative voltage power supply to divide the negative voltage supplied by the negative voltage power to output a plurality of negative gray scale voltages. An output unit; A positive voltage comprising a plurality of resistors and at least one variable resistor connected in series between the ground terminal and the positive voltage power supply to divide the positive voltage supplied by the positive voltage power to output a plurality of positive grayscale voltages. A gamma reference voltage circuit of a liquid crystal display device comprising an output unit. The method of claim 1, In the negative voltage output unit, a gamma reference voltage circuit of a liquid crystal display device, characterized in that one side of the variable resistor is connected in series to a negative voltage power supply, the other side is connected in series to a plurality of resistors. The method of claim 1, In the negative voltage output unit, one side of the variable resistor is connected in series with the ground terminal, the other side is a gamma reference voltage circuit of the liquid crystal display device, characterized in that connected in series. The method of claim 1, In the positive voltage output unit, one side of the variable resistor is connected in series with a positive voltage power supply, the other side is connected to a plurality of resistors in series gamma reference voltage circuit of the liquid crystal display device. The method of claim 1, In the positive voltage output unit, one side of the variable resistor is connected in series with the ground terminal, the other side is a gamma reference voltage circuit of the liquid crystal display device, characterized in that connected in series. The method of claim 1, And a voltage selector configured to receive the negative gray voltage and the positive gray voltage output from the negative voltage output unit and the positive voltage output unit to select and output any one of the negative gray voltage and the positive gray voltage. And a gamma reference voltage circuit of the liquid crystal display device. The method of claim 1, And amplifying part which receives and amplifies and outputs any one of a negative gray voltage and a positive gray voltage selected and selected by the selecting unit.