KR20070027872A - Gamma voltage circuit and driving method thereof, liquid crystal display using the same - Google Patents

Abstract

A gamma voltage circuit, a driving method thereof, and a liquid crystal display using the same are provided to control gamma voltages and brightness by generating the gamma voltages more than a desired number of gray scales and selecting the gamma voltages according to a brightness mode. A gamma voltage circuit includes a gamma voltage generation unit(20) and a gamma voltage selection unit(22). The gamma voltage generation unit generates gamma voltages of 2n times as much as a desired number of gray scales. The gamma voltage selection unit selectively supplies M gamma voltages which are selected from 2n+M gamma voltages according to a brightness mode. The M gamma voltages are increased or decreased in sequence.

Description

GAMMA VOLTAGE CIRCUIT AND DRIVING METHOD THEREOF, LIQUID CRYSTAL DISPLAY USING THE SAME

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

2 is a block diagram schematically illustrating a gamma voltage unit according to an exemplary embodiment of the present invention.

FIG. 3 is a data driving waveform diagram using a gamma voltage of a first brightness mode among the gamma voltages shown in FIG. 2.

4 is a data driving waveform diagram using a gamma voltage of a second brightness mode among the gamma voltages shown in FIG. 2.

FIG. 5 is a block diagram illustrating a liquid crystal display using the gamma voltage unit illustrated in FIG. 2.

<Description of Symbols for Main Parts of Drawings>

20: gamma voltage generator 22: gamma set selector

24: Timing Controller 26: Data Driver

28: gate driver 30: liquid crystal panel

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display, and more particularly, to a gamma voltage circuit capable of adaptively adjusting a gamma voltage according to a brightness mode required by a user, a driving method thereof, and a liquid crystal display using the same.

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 formed in each sub pixel region divided by an intersection of the gate line GL and the data line DL, the gate line GL, the data line DL, and the liquid crystal. A thin film transistor TFT connected between the cells 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 same 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 the nonlinear characteristic of the voltage versus luminance of the liquid crystal display, for example, the 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 liquid crystal display may use a method of adjusting a gamma curve, that is, a gamma voltage when brightness and visibility are required to be adjusted according to a user's request. However, when the gamma voltage is adjusted by adjusting the resistance of the gamma voltage unit, there is a problem in that a flicker phenomenon occurs due to a change in the kickback voltage of the common voltage.

Accordingly, an object of the present invention is to provide a gamma voltage circuit, a driving method thereof, and a liquid crystal display device using the same, which enables the brightness mode to be adjusted according to a user's request without flicker.

In order to achieve the above object, a gamma voltage circuit according to an embodiment of the present invention includes a gamma voltage generator for generating a gamma voltage as much as 2n (n is a natural number) than a desired gray number M (M is a natural number); And a gamma voltage selector configured to select and supply M gamma voltages sequentially increasing or decreasing among the 2n + M gamma voltages according to the brightness mode.

The gamma voltage generator generates n gamma voltages sequentially smaller than the first gamma voltage based on the first to Mth gamma voltages, and n gamma voltages sequentially larger than the Mth gamma voltage.

The gamma voltage generator generates 2n + M gamma voltages that increase or decrease in order from gamma voltage V0 to gamma voltage V2n + M-1.

In the first brightness mode, the gamma voltage selector decreases the M positive gamma voltages that increase in the gamma voltages Vn to Vn + M-1 according to the gray level, and decreases the gamma voltages Vn + M-1 to Vn in the gray level. M negative gamma voltages are selected.

The gamma voltage selector may include M positive gamma voltages that increase in the order of gamma voltages VO through VM-1 according to the gray level when the second brightness mode is brighter than the first brightness mode. M negative gamma voltages are selected in decreasing order of V2n.

The gamma voltage selector may include M positive gamma voltages that increase from gamma voltages V2n to V2n + M-1 according to the gray level in the third brightness mode darker than the first brightness mode, and VM-1 to V0 according to the gray level. M negative gamma voltages are sequentially selected.

In addition, the method for driving a gamma voltage circuit according to the present invention includes a first step of generating a gamma voltage as many as 2n (n is a natural number) than a desired gray number M (M is a natural number); And selecting and supplying M gamma voltages sequentially increasing among the 2n + M gamma voltages according to the brightness mode.

In addition, the liquid crystal display device using the gamma voltage circuit according to the present invention includes a liquid crystal panel for displaying an image; The gamma voltage circuit; A data driver which selects a corresponding gamma voltage among the gamma voltages supplied from the gamma voltage circuit and supplies the selected gamma voltage to a data line of the liquid crystal panel; And a common voltage generator configured to generate an AC common voltage and supply the alternating common voltage to the common electrode of the liquid crystal panel.

The common voltage generator generates an alternating gamma voltage having an amplitude greater than or equal to the entire range of the gamma voltage generated from the gamma voltage generator.

The common voltage generator generates an AC common voltage in which voltage levels are alternately changed in units of a horizontal synchronizing period.

Other objects and advantages of the present invention in addition to the above object will become apparent from the description of the preferred embodiment of the present invention with reference to the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to FIGS. 2 to 5.

2 is a block diagram schematically illustrating a gamma voltage circuit according to an exemplary embodiment of the present invention, and FIGS. 3 and 4 are driving waveform diagrams according to brightness modes.

The gamma voltage circuit shown in FIG. 2 includes a gamma voltage generator 20 that generates more gamma voltages than desired gray levels, and a gamma voltage selector 22 that selects a gamma voltage according to a brightness mode signal and supplies the gamma voltage to a data driver. Equipped.

The gamma voltage generator 20 generates more gamma voltages by 2n (n is a natural number) than the number of grays M (M is a natural number) to be displayed. In other words, the gamma voltage generator 20 further generates n gamma voltages symmetrically up and down with M gamma voltages corresponding to the normal brightness mode.

For example, when it is desired to display M = 64 gray levels, the gamma voltage generator 20 generates 2n + 64 gamma voltages, that is, gamma voltages V0 to gamma voltages V2n + 63. At this time, when it is assumed that the gamma voltage range corresponding to the normal brightness mode is Vn to Vn + 63, the gamma voltage generator 20 generates n gamma voltages VO to Vn-1 smaller than Vn and n greater than Vn + 63. More gamma voltages Vn + 64 to V2n + 63.

The gamma voltage generator 20 generates 2n + 64 gamma voltages by dividing the power supply voltage using a resistor string connected in series with the power supply line. In addition, the gamma voltage generator 20 divides the power supply voltage into a resistance string to generate a plurality of reference gamma voltages having a large interval, and then subdivides the plurality of reference gamma voltages into another resistance string again to form a small interval. It also generates 2n + 64 gamma voltages.

Accordingly, the gamma voltage generator 20 generates 2n + 64 gamma voltages that decrease or increase as the gamma voltage V0 goes to V2n + 63. For example, in the normally black mode, the voltage level increases from the gamma voltage V0 to V2n + 63. For convenience of description, only the case of the normally black mode will be described.

The gamma voltage selector 22 selects 64 gamma voltages from the Vn + 64 gamma voltages from the gamma voltage generator 20 and supplies them to the data driver according to the brightness mode signal from the outside.

For example, assume that the brightness mode is controlled to the normal first brightness mode, the brightest second brightness mode, and the dark third brightness mode.

In the first brightness mode at the normal brightness, the gamma voltage selector 22 converts the gamma voltages Vn to Vn + 63 positioned in the middle of the Vn + 64 gamma voltages from the gamma voltage generator 20 as the positive gamma voltage. Select and feed to the data driver. In addition, the gamma voltage selector 22 selects a gamma voltage Vn + 63 to Vn opposite to the level order of the positive gamma voltage as a negative gamma voltage and supplies it to the data driver. As described above, the use of the positive gamma voltage in which the level increases in the order of the gamma voltages Vn to Vn + 63 according to the gray level is used as the negative gamma voltage which decreases in the order of the gamma voltage Vn + 63 to Vn in accordance with the gray level. As shown in FIG. 1, the common voltage VCOM may be driven. In other words, when driving the common voltage VCOM as shown in FIG. 3, the gamma voltage Vn is selected as the lowest gray scale voltage of the positive polarity or the voltage of the highest gray scale of the negative polarity. The gamma voltage Vn + 63 is selected as the highest gray voltage of the positive polarity or the lowest gray voltage of the negative polarity.

Referring to FIG. 3, the high level and the low level of the common voltage VCOM are alternately supplied in units of a horizontal synchronization period H for driving a line inversion in which the liquid crystal cells of the liquid crystal panel are inverted in units of a horizontal line. do.

For example, when an arbitrary liquid crystal cell wants to display the lowest gray level, ie, the first gray level, as a positive voltage, the common electrode is supplied with a low level common voltage VCOM, and a gamma voltage Vn is selected to be displayed through the data line. It is supplied to the pixel electrode. As a result, the liquid crystal cell can display the first gray level by charging the pixel voltage of positive polarity, which is the difference voltage between the low level gamma voltage VCOM and the gamma voltage Vn.

On the other hand, when the liquid crystal cell displays the lowest gray level and the first gray level with a negative voltage, a high level common voltage VCOM is supplied to the liquid crystal panel, and a gamma voltage Vn + 63 is selected to form a liquid crystal through the data line. Supplied to the pixel electrode of the cell. As a result, the liquid crystal cell can display the first gray level by charging the pixel voltage of negative polarity, which is the difference voltage between the high level gamma voltage VCOM and the gamma voltage Vn + 63.

In addition, when the liquid crystal cell wants to display the highest gray level, ie, the 64th gray level, as a positive voltage, the common electrode is supplied with a low level common voltage VCOM, and a gamma voltage Vn + 63 is selected to form a pixel through the data line. Supplied to the electrode. As a result, the liquid crystal cell can display the 64th grayscale by charging the pixel voltage of positive polarity, which is the difference voltage between the low level gamma voltage VCOM and the gamma voltage Vn + 63.

In the brightest second brightness mode, the gamma voltage selector 22 converts the gamma voltages V0 to V63 from the gamma voltage generator 20 to the positive gamma voltage and the gamma voltage V2n. Select +63 to V2n as the negative gamma voltage to supply to the data driver. In other words, in the second brightness mode, the positive gamma voltage increases in the order of the gamma voltages V0 to V63 according to the gray level, and the negative gamma voltage decreases in the order of the gamma voltages V2n + 63 to V2n according to the gray level. Is selected and used. Accordingly, when the common voltage VCOM is AC-driven as shown in FIG. 4, the gamma voltage V0 is selected as the lowest gray level voltage of positive polarity, the gamma voltage V2n + 63 is selected as the lowest gray level voltage of negative polarity, and the gamma voltage V63 is defined as the electrodelographic characteristic. As the highest gradation voltage, the gamma voltage V2n is selected as the highest gradation voltage of negative polarity.

Referring to FIG. 4, a high level and a low level of the common voltage VCOM are alternately supplied in units of a horizontal synchronization period H for driving a line inversion in which liquid crystal cells of the liquid crystal panel are inverted in units of a horizontal line. do.

For example, when an arbitrary liquid crystal cell wants to display the lowest gray level, ie, the first gray level, as a positive voltage, the common electrode is supplied with a low level common voltage VCOM, and a gamma voltage V0 is selected to be displayed through the data line. It is supplied to the pixel electrode. As a result, the liquid crystal cell can display the first gray level by charging the pixel voltage of positive polarity, which is the difference voltage between the low level gamma voltage VCOM and the gamma voltage V0.

On the other hand, when the liquid crystal cell displays the lowest gray level and the first gray level with a negative voltage, a high level common voltage VCOM is supplied to the liquid crystal panel, and a gamma voltage V2n + 63 is selected to form a liquid crystal through the data line. Supplied to the pixel electrode of the cell. As a result, the liquid crystal cell can display the first gray level by charging the pixel voltage of negative polarity, which is the difference voltage between the high level gamma voltage VCOM and the gamma voltage V2n + 63.

In addition, when the liquid crystal cell wants to display the highest gray level, ie, the 64th gray level, as the positive voltage, the common voltage VCOM of the low level is supplied to the common electrode, and the gamma voltage V63 is selected to the pixel electrode through the data line. Supplied. As a result, the liquid crystal cell can display the 64th grayscale by charging the pixel voltage of positive polarity which is the difference voltage between the low level gamma voltage VCOM and the gamma voltage V63.

In the dark third brightness mode, the gamma voltage selector 22 converts the gamma voltages V2n to V2n + 63 of the Vn + 64 gamma voltages from the gamma voltage generator 20 as the positive gamma voltage. V63 to V0 are selected as negative gamma voltages and supplied to the data driver. In other words, in the third brightness mode, the positive gamma voltage increases in the order of the gamma voltages V2n to V2n + 63 according to the gray level, and the negative gamma voltage decreases in the order of the gamma voltages V63 to V0 according to the gray level. Is selected and used. Accordingly, when the common voltage VCOM is alternatingly driven, the gamma voltage V2n is selected as the lowest gray scale voltage of positive polarity, the gamma voltage V63 is selected as the negative gray scale voltage of negative polarity, and the gamma voltage V2n + 63 is set to the highest gray scale voltage of positive polarity. The gamma voltage V0 is selected as the highest gradation voltage of negative polarity.

As described above, the gamma voltage circuit according to the present invention can symmetrically generate as many gamma voltages as desired by 2n than the desired number of gray levels, thereby adjusting the gamma voltage by selecting the gamma voltage according to the brightness mode. At this time, the amplitude of the common voltage VCOM driven by the AC is set to be greater than or equal to the range V0 to V2n + 63 of the entire gamma voltage, thereby preventing the kickback voltage of the common voltage from changing.

FIG. 5 is a block diagram illustrating a liquid crystal display according to the present invention using the gamma voltage circuit shown in FIG. 2.

5 illustrates a gate driver 28 for driving the gate line GL of the liquid crystal panel 30, a data driver 26 for driving the data line DL, and a gamma voltage. A gamma voltage generator 20, a gamma voltage selector 22 which selects a gamma voltage according to a brightness mode, and supplies the gamma voltage to the data driver 26, a data driver 26, a gate driver 28, and a gamma voltage selection. A timing controller 24 for controlling the unit 22 is provided. In addition, the liquid crystal display further includes a common voltage generator (not shown) for generating an AC common voltage VCOM under the control of the timing controller 24 and supplying the alternating common voltage VCOM to the common electrode of the liquid crystal panel 30.

The timing controller 24 generates control signals for controlling the driving of the common voltage generator and the gate driver 28 and the data driver 26 by using a vertical synchronization signal, a horizontal synchronization signal, a dot clock signal, etc. input from the outside. . In addition, the timing controller 24 aligns the input data signal according to the dot clock signal and supplies it to the data driver 26. The timing controller 24 generates a brightness mode signal according to a user's request and supplies it to the gamma set selector 22.

The gamma voltage generator 20 generates gamma voltages, that is, gamma voltages V0 to V2n + 63, which are as many as 2n than the desired number of gray levels as shown in FIG.

The gamma voltage selector 22 selects and supplies a gamma voltage from the gamma voltage generator 20 to the data driver 26 according to the brightness mode signal from the timing controller 24.

The data driver 26 selects the gamma voltage supplied through the gamma voltage selector 22 according to the digital data signal from the timing controller 24 and supplies the gamma voltage to the data line DL. At this time, the data driver 26 selects the positive or negative gamma voltage according to the polarity control signal from the timing controller 24 and supplies the selected data to the data line DL.

The data driver 26 may be integrated into one driving chip together with the gamma voltage generator 20 and the gamma voltage selector 22.

The gate driver 28 generates a scan signal according to a control signal from the timing controller 24 and supplies the scan signal to the gate line GL.

The liquid crystal panel 30 includes a liquid crystal cell Clc formed at each sub pixel area divided by an intersection of the gate line GL and the data line DL, and the gate line GL, the data line DL, and the liquid crystal cell Clc. A thin film transistor (TFT) connected therebetween 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.

As described above, the gamma voltage circuit and the driving method thereof according to the present invention, and the liquid crystal display using the same, generate more gamma voltages than desired gradations and select them according to the brightness mode, thereby changing the kickback voltage without changing the kickback voltage. You can adjust the brightness by adjusting the gamma voltage.

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

Claims (15)

A gamma voltage generator for generating a gamma voltage by 2n (n is a natural number) than a desired gray number M (M is a natural number); And a gamma voltage selector configured to select and supply M gamma voltages sequentially increasing or decreasing among the 2n + M gamma voltages according to a brightness mode. The method of claim 1, The gamma voltage generator A gamma voltage circuit which generates n gamma voltages sequentially smaller than a first gamma voltage based on the first to Mth gamma voltages, and n gamma voltages sequentially larger than the Mth gamma voltage. The method of claim 2, The gamma voltage generation unit generates a gamma voltage of 2n + M gamma voltages that increase or decrease in order from gamma voltage V0 to gamma voltage V2n + M-1. The method of claim 3, wherein The gamma voltage selector In the first brightness mode, M positive gamma voltages increase in the order of gamma voltage Vn to Vn + M-1 according to the gray level, and M negative polarities decrease in the order of gamma voltage Vn + M-1 to Vn according to the gray level. A gamma voltage circuit, characterized in that for selecting a gamma voltage. The method of claim 4, wherein In the second brightness mode, which is brighter than the first brightness mode, M positive gamma voltages that increase in the order of gamma voltages VO to VM-1 according to the gray level are decreased in the order of V2n + M-1 to V2n according to the gray level. And a gamma voltage circuit for selecting two negative gamma voltages. The method of claim 5, In the third brightness mode that is darker than the first brightness mode, M positive gamma voltages that increase in the gamma voltage V2n to V2n + M-1 according to the gray level are decreased in the order of VM-1 to V0 according to the gray level. And a gamma voltage circuit for selecting two negative gamma voltages. Generating a gamma voltage by as many as 2n (n is a natural number) than a desired gray number M (M is a natural number); And selecting and supplying M gamma voltages sequentially increasing among the 2n + M gamma voltages according to the brightness mode. The method of claim 7, wherein The first step is Generating n gamma voltages sequentially smaller than a first gamma voltage based on the first to Mth gamma voltages, and n gamma voltages sequentially larger than the Mth gamma voltage. Method of driving a voltage circuit. The method of claim 8, The first step is And generating 2n + M gamma voltages that increase or decrease in order from gamma voltage V0 to gamma voltage V2n + M-1. The method of claim 9, The second step is In the first brightness mode, M positive gamma voltages increase in the order of gamma voltage Vn to Vn + M-1 according to the gray level, and M negative polarities decrease in the order of gamma voltage Vn + M-1 to Vn according to the gray level. And selecting a gamma voltage. The method of claim 10, The second step is In the second brightness mode, which is brighter than the first brightness mode, M positive gamma voltages that increase in the order of gamma voltages VO to VM-1 according to the gray level are decreased in the order of V2n + M-1 to V2n according to the gray level. And selecting two negative gamma voltages. The method of claim 11, In the third brightness mode that is darker than the first brightness mode, M positive gamma voltages that increase in the gamma voltage V2n to V2n + M-1 according to the gray level are decreased in the order of VM-1 to V0 according to the gray level. And selecting two negative gamma voltages. A liquid crystal panel which displays an image; A gamma voltage circuit according to any one of claims 1 to 6; A data driver which selects a corresponding gamma voltage among the gamma voltages supplied from the gamma voltage circuit and supplies the selected gamma voltage to a data line of the liquid crystal panel; And a common voltage generator configured to generate an alternating common voltage and supply the alternating common voltage to the common electrode of the liquid crystal panel. The method of claim 13, The common voltage generator And generating an alternating gamma voltage having an amplitude greater than or equal to the entire range of the gamma voltage generated from the gamma voltage generator. The method of claim 13, The common voltage generator And an alternating current common voltage in which voltage levels are alternately changed in units of a horizontal synchronizing period.

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