KR20080032694A - Method and apparatus for generating gamma voltage - Google Patents

Abstract

A method and an apparatus for generating a gamma voltage are provided to improve image quality by maintaining a gamma curve even when an analog voltage is varied. An LCD(Liquid Crystal Display) device includes a gate driver(102), a data driver(106), a gamma voltage generator(100), a timing controller(108), and a power source(110). The gate driver drives gate lines of an LCD panel. The data driver drives data lines. The gamma voltage generator generates a gamma voltage and drives the data driver. The timing controller controls the data and gate drivers. The power source generates plural driving voltages for circuit blocks and supplies the voltages to the circuit blocks. An external driving voltage is supplied to the power source. The driving voltage is supplied to the timing controller and data and gate drivers. The power source generates a gate-on voltage, a gate-off voltage, and an analog voltage and supplies the voltages to the LCD panel.

Description

Gamma voltage generation method and apparatus {METHOD AND APPARATUS FOR GENERATING GAMMA VOLTAGE}

1 is an equivalent circuit diagram of one sub-pixel of a conventional liquid crystal display.

2 is a block diagram illustrating a liquid crystal display according to an exemplary embodiment of the present invention.

3 is a block diagram illustrating a gamma voltage generation method according to the present invention.

4 illustrates a gamma curve when the driving voltage of the liquid crystal display according to the exemplary embodiment of the present invention is changed.

5 is a block diagram illustrating a gamma voltage generator according to an exemplary embodiment of the present invention.

<Code Description of Main Parts of Drawing>

100 gamma voltage generator 102 liquid crystal panel

104: gate driver 106: data driver

108: timing control unit 110: power supply unit

200: I2C interface 202: data register

204: memory 206: logic circuit

208: DAC part

The present invention relates to a method and apparatus for generating gamma voltage, and more particularly, to a method and apparatus for generating gamma voltage capable of generating a stable gamma curve even with analog voltage changes.

The liquid crystal display displays an image by adjusting the light transmittance of the liquid crystal having dielectric anisotropy according to the electric field. The liquid crystal display includes an active matrix type liquid crystal panel in which thin film transistors are formed in each liquid crystal cell, and a driving circuit for driving the liquid crystal panel.

As shown in FIG. 1, the liquid crystal panel includes a liquid crystal cell Clc, a gate line GL, a data line DL, and a liquid crystal cell formed in each sub pixel area divided by the intersection of the gate line GL and the data line DL. The thin film transistor TFT connected between (Clc) is provided.

The thin film transistor TFT supplies the data signal of the data line DL to the liquid crystal cell Clc in response to the scan signal of the gate line GL. The liquid crystal cell Clc charges the pixel voltage, which is the difference between the supplied data signal and the common voltage Vcom, and drives the liquid crystal according to the charged pixel voltage to adjust the light transmittance. In this case, in order to stably maintain the pixel voltage charged in the liquid crystal cell Clc, a storage capacitor Cst connected in parallel with the liquid crystal cell Clc is further provided.

The driving circuit includes a gate driver for driving the gate line GL and a data driver for driving the data line DL. The gate driver supplies scan signals sequentially to the gate lines GL. The data driver converts a digital data signal into an analog voltage and supplies the data signal to the data line DL whenever the scan signal is supplied to the gate line GL.

In this case, the data driver converts the digital data signal into an analog signal using a plurality of gamma voltages having different levels for each gray level. In other words, the data driver selects a gamma voltage corresponding to the gray value of the digital data signal and supplies it to the data line. In this case, the data driver selects a positive or negative polarity (based on Vcom) gamma voltage according to the polarity control signal for inversion driving and supplies the data to the data line.

To this end, the gamma voltage unit generates the positive and negative gamma voltages preset for each gray level according to a nonlinear characteristic of voltage versus luminance of the liquid crystal display, for example, a 2.2 gamma curve, and supplies them to the data driver. The gamma voltage unit typically generates positive and negative gamma voltages by dividing by using a resistor string connected in series with a power supply line.

The conventional method of making a gamma reference voltage produces a gamma curve based on a fixed analog voltage AVDD. However, this method has a problem in that the gamma curve is also distorted when the analog voltage AVDD is changed.

Accordingly, an aspect of the present invention is to provide a method and apparatus for generating a gamma voltage capable of generating a gamma curve that is stable even with an analog voltage change.

In order to achieve the above technical problem, the gamma voltage generation method of the present invention comprises the steps of storing the first analog voltage in the memory; Storing the input second analog voltage in a memory; Generating gamma correction data through the second analog voltage; Comparing the first analog voltage with the second analog voltage; Comparing the first analog voltage with the second analog voltage and generating a gamma voltage through the first analog voltage if there is no voltage difference; And comparing the first analog voltage with the second analog voltage to generate the gamma corrected gamma voltage when there is a voltage difference.

The comparing of the first analog voltage and the second analog voltage may include generating an enable signal; Storing the second analog voltage in the memory when the enable signal is input.

The storing of the second analog voltage in a memory may include converting and storing the second analog voltage into digital data.

Generating the gamma correction data may include estimating any one of white and black voltages by adding a difference between neighboring gamma voltages.

In order to achieve the above technical problem, the gamma voltage generator of the present invention

A memory in which the first analog voltage data is input and stored; A data register for storing second analog voltage data input from the outside; Comprising by comparing the first analog voltage data and the second analog voltage data, if there is a difference corrects, and generates and stores the gamma voltage data in the memory and at the same time generating a signal for outputting the corrected gamma voltage It features.

The logic circuit unit estimates one of white or black voltages by adding a difference between neighboring gamma voltages.

And a digital-analog converter for converting the corrected gamma voltage data input from the logic circuit to an analog.

Other technical problems and features of the present invention in addition to the above technical problem will become 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 the accompanying drawings.

2 is a block diagram illustrating a liquid crystal display according to an exemplary embodiment of the present invention.

The liquid crystal display illustrated in FIG. 2 generates a gate driver 102 for driving the gate line GL of the liquid crystal panel 100, a data driver 106 for driving the data line DL, and a gamma voltage. The gamma voltage generator 100 for supplying the data driver 106, the timing controller 108 for controlling the data driver 106 and the gate driver 104, and a plurality of driving voltages required for the respective circuit blocks. It is provided with a power supply unit 110 to generate and supply.

The power supply unit 110 is supplied with a driving voltage VDD from the outside, and the driving voltage VDD is supplied to the timing controller 108 including the digital circuit, the data driver 106 and the gate driver 104 as a digital drive voltage. Supplied. The power supply unit 110 generates the gate-on voltage VON, the gate-off voltage VOFF, the analog voltage AVDD, and the like, using the driving voltage VDD from the outside, and supplies them to the liquid crystal panel 102.

The timing controller 108 controls a plurality of control signals for controlling the driving timing of the gate driver 104 and the data driver 106 by using a vertical synchronization signal, a horizontal synchronization signal, a dot clock, a data enable signal, etc. input from the outside. Occurs.

The gate driver 104 generates a scan signal according to a control signal from the timing controller 108 and supplies the scan signal to the gate line GL. In detail, the gate driver 104 selects the gate-on voltage VON of the power supply unit 110 to the gate line GL according to a control signal from the timing controller 108, and supplies the gate-off voltage VOFF) is selected and supplied to the gate line GL.

The gamma voltage generator 100 generates a reference voltage used to generate the gamma voltage and supplies the generated reference voltage to the data driver 106.

In detail, the gamma voltage generator 100 generates a plurality of gamma reference voltages through the analog voltage AVDD received from the power supply unit 110 and subdivids them by gray levels to generate positive and negative gamma voltages. Analog conversion (DAC) converts digital data into analog signals and feeds them to data lines.

The data driver 106 selects a gamma voltage according to the digital data signal from the timing controller 108 and supplies the gamma voltage to the data line DL of the liquid crystal panel 102.

3 is a block diagram illustrating a gamma voltage generation method according to the present invention.

Referring to FIG. 3, the method of generating a gamma voltage may include storing a first analog voltage and a second analog voltage in a memory (S10), and generating gamma correction data through a second analog voltage stored in the memory (S20). ), And if there is no voltage difference between the first analog voltage and the second analog voltage, generating gamma voltages through the first analog voltage (S30, S40, S50), and generating the gamma voltage through the first analog voltage and the second analog voltage. Generating the gamma corrected gamma voltage when there is a voltage difference (S30, S20, S10, S30, S40, and S50).

The method may further include generating an enable signal at step S30 of comparing the first analog voltage with the second analog voltage.

The first analog voltage AVDD1 data from the power supply unit 110 is stored in the memory 204. The second analog voltage AVDD2 is input from the outside and stored in the memory 204. This is because EDID (Extended Display Identification Data) information for the liquid crystal panel 102 stored in a part of the memory 204 and the communication by the I2C interface 200 method are used to convert the second analog voltage (AVDD2) data into the data register 202. Are stored in. The memory 204 in which data is stored preferably uses EEPROM (Electrically Erasable Programmable Read Only Memory).

Subsequently, gamma correction data is generated through the second analog voltage AVDD2 stored in the memory. Then, the first analog voltage AVDD1 and the second analog voltage AVDD2 are compared. The method may further include generating an enable signal in the comparing of the first and second analog voltages AVDD1 and AVDD2, and storing the second analog voltage AVDD2 in the memory when the enable signal is input.

Then, in the step of storing the first or second analog voltage AVDD1 or AVDD2 in the memory, the first or second analog voltage AVDD1 or AVDD2 is converted into digital data and stored.

In this case, if there is no voltage difference between the first analog voltage AVDD1 and the second analog voltage AVDD2, a gamma voltage is generated through the first analog voltage AVDD1. On the other hand, if there is a voltage difference between the first analog voltage AVDD1 and the second analog voltage AVDD2, the gamma voltage is fed back to step S10 through the gamma correction data generated through the second analog voltage AVDD2 to generate a gamma voltage whose gamma value is corrected. do.

4 illustrates a gamma curve when the driving voltage of the liquid crystal display according to the exemplary embodiment of the present invention is changed.

Referring to FIG. 4, when the analog voltage AVDD is increased, the gamma value is larger than the reference gamma curve 50 having a gamma value of 2.2, and thus is formed like the first gamma curve 60. On the other hand, when the analog voltage AVDD decreases, the gamma value becomes smaller than the reference gamma curve 50, and thus is formed like the second gamma curve 70.

It is important to create an algorithm that determines the magnitude of the gamma voltage accordingly when the analog voltage AVDD changes. This concept changes the other gamma voltage accordingly by changing only the black side voltage. The difference between two neighboring gamma voltages is maintained while maintaining a constant magnitude. However, estimating how much the black voltage should change is difficult unless you actually measure the gamma curve. So we have to estimate the other gamma voltage first and then estimate the black voltage accordingly. In other words, starting from the white voltage based on the center value of gamma, and continuing to add as much as the voltage difference between both ends, finally, VGMA1 and VGMA11 are estimated.

As shown in Table 1 below, for example, 12 gamma reference voltages will be described by solving the above-described contents with an equation.

Point Gamma voltage Difference between two ends Difference between two ends AVDD One VGMA1 AVDD-VGMA1 2 VGMA2 VGMA1-VGMA2 3 VGMA3 VGMA2-VGMA3 4 VGMA4 VGMA3-VGMA4 5 VGMA5 VGMA4-VGMA5 6 VGMA6 VGMA5-VGMA6 GCNT GCNT VGMA6-GCNT 7 VGMA7 GCNT-VGMA7 8 VGMA8 VGMA7-VGMA8 9 VGMA9 VGMA8-VGMA9 10 VGMA10 VGMA9-VGMA10 11 VGMA11 VGMA10-VGMA11 12 VGMA12 VGMA11-VGMA12

The magnitude of each voltage can be known by the input analog voltage AVDD.

Where VGMAn = nth gamma, Gn = nth data, 2 ^ i = total input data size, VRn = nth variable resistor, VRt = total variable resistor

Therefore, it can be seen that the difference of each data value is the difference of the gamma reference voltage between both ends.

Where n = 1, VGMAn = AVDD, n = 6, VGn + 1 = GCNT,

        If n = 7 then VGn = GCNT voltage.

In order to simplify the equation, the variable resistor part is a common part, so it will be omitted and explained.

Here, Δ2 and Δ12 are values to be estimated and are not stored.

The equation when the analog voltage AVDD is fluctuated is as follows. To illustrate the positive polarity, first of all, the VGMA6 value is

The remaining gamma voltage is

And the VGMA1 value is

The negative polarity may also be obtained in this manner.

5 is a block diagram illustrating a gamma voltage generator according to an exemplary embodiment of the present invention.

Referring to FIG. 5, the gamma voltage generator includes a memory 204 in which first analog voltage VDD1 data is input and stored, and a data register 202 in which second analog voltage VDD2 data input from the outside is stored. And a logic for comparing the first analog voltage VDD1 and the second analog voltage VDD2 data and correcting any differences, generating the gamma voltage data, storing the data in the memory, and simultaneously outputting the corrected gamma voltage. And a circuit portion 206.

Here, the logic circuit unit 206 estimates the voltage of either white or black by adding the difference of neighboring gamma voltages.

In addition, a digital-to-analog converter (DAC unit) for converting the corrected gamma voltage data input from the logic circuit unit 206 to analog.

Specifically, the first analog voltage VDD1 data is stored in the memory. Extended display identification data (EDID) information for the liquid crystal panel 102 stored in a portion of the memory 204 and the second analog voltage (AVDD2) data inputted through communication using the I2C interface 200 method are stored in the data register 202. ) The memory 204 in which data is stored preferably uses EEPROM (Electrically Erasable Programmable Read Only Memory).

The analog voltage AVDD may be an input second analog voltage VDD2 or may be data input through an enable signal.

The logic circuit unit 206 compares the first analog voltage VDD1 and the second analog voltage VDD2 data. The second analog voltage AVDD2 stored in the data register 202 and the first analog voltage AVDD1 stored in the memory 204 are compared, and if there is no difference between the first and second analog voltages AVDD1 and AVDD2, A gamma voltage is generated from the first analog voltage AVDD1 data, and if a difference between the first and second analog voltages AVDD1 and AVDD2 occurs, the corrected gamma voltage is output.

The correction of the gamma voltage is performed by estimating the voltage of either white or black by adding the difference of neighboring gamma voltages.

The gamma voltage thus generated is converted by the digital-to-analog converter (DAC) into gamma voltage data to an analog signal and supplied to the data lines.

As described above, the method and apparatus for generating gamma voltage according to the present invention can maintain a stable gamma curve by generating a gamma voltage corrected through gamma voltage compensation data even when an analog voltage changes, thereby improving display quality. .

Although the detailed description of the present invention described above has been described with reference to a preferred embodiment of the present invention, those skilled in the art or those skilled in the art, those skilled in the art, described in the claims below It will be understood that various modifications and changes can be made in the present invention without departing from the spirit and scope of the invention.

Claims (7)

Storing the first analog voltage in a memory; Storing the input second analog voltage in a memory; Generating gamma correction data through the second analog voltage; Comparing the first analog voltage with the second analog voltage; Comparing the first analog voltage with the second analog voltage and generating a gamma voltage through the first analog voltage if there is no voltage difference; And comparing the first analog voltage with the second analog voltage to generate the gamma corrected gamma voltage if there is a voltage difference. The method of claim 1, Comparing the first analog voltage and the second analog voltage is Generating an enable signal; And when the enable signal is input, storing a second analog voltage in the memory. The method of claim 2, The storing of the second analog voltage in the memory And converting and storing the second analog voltage into digital data. The method of claim 1, Generating the gamma correction data Estimating a voltage of either white or black by adding a difference between neighboring gamma voltages. A memory in which the first analog voltage data is input and stored; A data register for storing second analog voltage data input from the outside; Comprising by comparing the first analog voltage data and the second analog voltage data, if there is a difference corrects, and generates and stores the gamma voltage data in the memory and at the same time generating a signal for outputting the corrected gamma voltage Gamma voltage correction device characterized in that. The method of claim 5, wherein And the logic circuit unit estimates one of white or black by adding a difference between neighboring gamma voltages. The method of claim 5, wherein And a digital-analog converter configured to convert the corrected gamma voltage data input from the logic circuit to an analog.

Images