KR101322006B1 - Liquid crystal display and method for correcting a gamma thereof - Google Patents

Abstract

The present invention relates to a liquid crystal display device having a backlight unit.

The liquid crystal display includes a liquid crystal display panel in which a plurality of data lines and a plurality of gate lines intersect and liquid crystal cells are arranged in a matrix form; A plurality of light sources for irradiating light onto the liquid crystal display panel; A source driver converting digital video data into an analog data voltage based on a gamma compensation voltage and supplying the digital video data to the data lines; A gate driver sequentially supplying a gate pulse to the gate lines; And gamma compensation voltages of the first display surfaces of the liquid crystal display panel at positions opposite to the light sources, and gamma compensation voltages of the second display surfaces of the liquid crystal display panel between the first display surfaces. The gamma correction part which generate | occur | produces is provided. The gamma compensation voltages of the first display surfaces and the gamma compensation voltages of the second display surfaces are different from each other.

Description

Liquid crystal display and its gamma correction method {LIQUID CRYSTAL DISPLAY AND METHOD FOR CORRECTING A GAMMA THEREOF}

The present invention relates to a liquid crystal display device having a backlight unit.

BACKGROUND ART [0002] Liquid crystal display devices are becoming increasingly widespread due to features such as light weight, thinness, and low power consumption driving. This liquid crystal display device is used as a portable computer such as a notebook PC, an office automation device, an audio / video device, and an indoor / outdoor advertisement display device. A transmissive liquid crystal display device that occupies most of the liquid crystal display device controls an electric field applied to the liquid crystal layer to modulate light incident from the backlight unit to display an image.

The backlight unit is divided into a direct type and an edge type. In the edge type backlight unit, a lamp is disposed under an edge of the liquid crystal display panel, and a light guide plate and a plurality of optical sheets are disposed between the liquid crystal display panel and the lamp.

The direct type backlight unit installs a plurality of lamps under the liquid crystal display panel, and arranges a diffusion plate and a plurality of optical sheets between the lamps and the liquid crystal display panel. The diffusion plate is used for the purpose of making the luminance of the display surface uniform by diffusing light incident from the lamp. In the direct type backlight unit, the distance between the light source and the diffuser plate must be long for the diffuser plate to sufficiently diffuse the light. However, due to the trend toward thinner liquid crystal displays, the distance between the diffuser and the lamp in the backlight unit is narrowed, so that a brighter lamp appears to the viewer. In order to improve such a bright line problem, a method of increasing the number of lamps, a method of reinforcing the diffusion sheet in the optical sheet, such as forming a fine prism pattern or a lens pattern on the diffusion plate facing the liquid crystal display panel, and a method of reinforcing the diffusion sheet However, these methods also have a problem in that there is a limit to increase the light diffusion and cause a cost increase.

Disclosure of Invention An object of the present invention is to provide a liquid crystal display and a gamma correction method for reducing a bright line by compensating gamma compensation voltage using a simple circuit.

According to an exemplary embodiment of the present invention, a liquid crystal display device includes: a liquid crystal display panel in which a plurality of data lines and a plurality of gate lines intersect and liquid crystal cells are arranged in a matrix; A plurality of light sources for irradiating light onto the liquid crystal display panel; A source driver converting digital video data into an analog data voltage based on a gamma compensation voltage and supplying the digital video data to the data lines; A gate driver sequentially supplying a gate pulse to the gate lines; And gamma compensation voltages of the first display surfaces of the liquid crystal display panel, which are at positions opposite to the light sources, and gamma compensation voltages of the second display surfaces of the liquid crystal display panel, which exist between the first display surfaces. The gamma correction part which generate | occur | produces is provided. The gamma compensation voltages of the first display surfaces and the gamma compensation voltages of the second display surfaces are different from each other.

The gamma correction unit changes the gamma compensation value according to the gray level of the digital video data.

The liquid crystal display further includes a timing controller which generates a control signal for controlling the gamma correction unit and controls operation timings of the source driver and the gate driver.

The timing controller may include an option terminal configured to receive one of a high logic voltage and a low logic voltage to generate an option signal; A gray scale determination unit configured to analyze digital video data of an input image and determine a gray scale of the digital video data; A display position determining unit which determines a display position of the digital video data based on an input timing signal; A memory storing a lookup table having a gamma compensation value determined according to a gray level of the digital video data; A gamma correction control signal generator for generating a control signal of a gamma correction mode by selecting the gamma compensation value from the lookup table according to the output of the gray scale determination unit and the display position determination unit; And a selector configured to select one of the control signal of the non-gamma correction mode and the control signal of the gamma correction mode according to the option signal to generate the control signal.

The gamma correction unit increases the correction width of the gamma compensation voltage when the gray level of the digital video data is an intermediate gray level, compared to the low gray level and the high gray level.

The gamma correction unit includes: a first voltage dividing circuit for dividing a first power voltage; A second voltage dividing circuit for dividing a second power voltage different from the first power voltage; A first selector configured to select one of an output of the first voltage divider circuit and an output of the second voltage divider circuit in response to the control signal to generate the gamma compensation voltage; A power adjuster configured to correct the first power voltage by different correction widths according to the gray levels to generate a plurality of corrected power voltages separated by gray levels; And a second selector configured to select one of the corrected power supply voltages and generate the second power supply voltage in response to the control signal.

A gamma correction method of a liquid crystal display according to an exemplary embodiment of the present invention includes a luminance difference between first display surfaces of the liquid crystal display panel corresponding to the light sources and second display surfaces positioned between the first display surfaces. Inspecting; And generating the gamma compensation voltage by differently performing a gamma compensation value of the first display surface and a gamma compensation value of the second display surface.

The liquid crystal display and the gamma correction method according to an exemplary embodiment of the present invention selectively correct analog analog gamma compensation values according to display positions without using complicated logic circuits for modulating digital video data. As a result, the liquid crystal display device and the gamma correction method according to the embodiment of the present invention are located between the display surface of the bright line corresponding to the lamps and the lamps in the liquid crystal display device employing the direct type backlight unit, so that the luminance is relatively high. The luminance of the entire display surface may be uniform by correcting the analog gamma compensation value supplied to the liquid crystal cells of any one of the lower display surfaces.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to FIGS. 1 to 8.

1 to 3, a liquid crystal display according to an exemplary embodiment of the present invention includes a liquid crystal display panel 10, a backlight unit 20 for irradiating light to the liquid crystal display panel 10, and a backlight unit 20. Driving the backlight driver 21 for driving the light sources, the source driver 12 for driving the data lines 14 of the liquid crystal display panel 10, and the gate lines 15 of the liquid crystal display panel 10. Selects the gate driver 13, the power supply 40 generating the driving voltages Vgh, Vgl, GMA1 to GMAn, and Vcom supplied to the liquid crystal display panel 10, and the gamma compensation reference voltages GMA1 to GMAn. And a gamma correction unit 41 for correcting.

In the liquid crystal display panel 10, a liquid crystal layer is formed between two glass substrates. A plurality of data lines 14 and a plurality of gate lines 15 intersect the lower glass substrate of the liquid crystal display panel 10. The liquid crystal cells Clc are arranged in a matrix form on the liquid crystal display panel 10 due to the cross structure of the data lines 14 and the gate lines 15. The pixel electrode 1 of the liquid crystal cell Clc connected to the data lines 14, the gate lines 15, the thin film transistor TFT, and the thin film transistor TFT is disposed on the lower glass substrate of the liquid crystal display panel 10. , And a storage capacitor Cst and the like are formed.

On the upper glass substrate of the liquid crystal display panel 10, a black matrix, a color filter, and a common electrode 2 are formed. The common electrode 2 is formed on an upper glass substrate in a vertical electric field driving mode such as a TN (Twisted Nematic) mode and a VA (Vertical Alignment) mode. The common electrode 2 is formed of an IPS (In Plane Switching) mode, an FFS (Fringe Field Switching) Is formed on the lower glass substrate together with the pixel electrode 1 in the same horizontal electric field driving system. On the upper glass substrate and the lower glass substrate of the liquid crystal display panel 10, a polarizing plate is attached and an alignment film for forming a pre-tilt angle of the liquid crystal is formed on the inner surface in contact with the liquid crystal.

The backlight unit 20 irradiates the liquid crystal display panel 10 with light from light sources driven by the backlight driver 21. The backlight unit 20 includes a plurality of lamps 31, a bottom cover 32 in which the lamps 31 are accommodated, a diffusion plate 33 covering an opening of the bottom cover 32, and a diffusion plate 33. And arranged optical sheets 34. The lamps 31 emit light by the AC voltage supplied from the inverter of the backlight driver and irradiate light toward the diffusion plate 33. The lamp 31 may be selected from a cold cathode fluorescent lamp (CCFL) or an external electrode fluorescent lamp (EEFL). The bottom cover 32 is made of a container structure to accommodate a plurality of lamps 31, the reflective sheet is attached to the bottom and side of the inner space. The diffusion plate 33 is assembled to the bottom cover 32 so as to cover the opening of the bottom cover 32 in which the lamps 31 are accommodated. The diffuser plate 33 incorporates a plurality of beads and scatters incident light from the lamps 31 and reflected light from the reflective sheet attached to the bottom cover 32 to the optical sheets 34. Diffuse light. The optical sheets 34 include one or more diffusion sheets and one or more prism sheets to diffuse light incident from the diffusion plate 33 and to fold light propagation path toward the display surface of the liquid crystal display panel 10. Do it. Light propagating from the backlight unit 20 toward the liquid crystal display panel 10 is uneven due to the luminance difference between the lamps 31 and them. For example, even when data of the same gradation is displayed on the entire display surface of the liquid crystal display panel 10 in a state where the liquid crystal display panel 10 and the backlight unit 20 are assembled, the lamps 31 may be arranged along the shape of the lamps 31. Bright lines appear brighter than the display plane between). The brightness of the bright line depends on the gradation. For example, when the maximum gray scale of the image displayed on the liquid crystal display panel 10 is 256, the bright line is clearly seen in the middle gray scale range of 64 to 127 gray scales, and the luminance is relatively small in the low gray scale range lower than 64 gray scales. On the other hand, it is hardly seen in the high gradation range above 127 gradations. In other words, when the maximum gradation of the image is 100%, the bright line is clearly seen in the image of the middle gradation range of about 25% to 50%, and the relatively small luminance is shown in the low gradation range lower than 25%.

The backlight driver 21 controls the brightness of the lamps 31 according to the dimming signal DIM from the timing controller 11. For example, in a bright image, the timing controller 11 generates a dimming signal DIM having a relatively high value, and according to the dimming signal DIM, the backlight driver 21 causes the light source lighting ratio or pulses of the lamps 31 to lie. The brightness of the display surface on which a bright image is displayed is increased by increasing the width modulation ratio (PWM%). On the other hand, in a relatively dark image, the timing controller 11 generates a dimming signal DIM having a relatively low value, and the backlight driver 21 lights up the light sources of the lamps 31 according to the dimming signal DIM. Lowering the ratio lowers the luminance of the display surface on which the dark image is displayed.

The source driver 12 latches the digital video data RGB under the control of the timing controller 11. The source driver 12 converts the digital video data RGB into the positive / negative analog data voltage using the positive / negative gamma compensation reference voltages GMA1 to GMAn and supplies them to the data lines 14. do.

The gate driver 13 includes a shift register, a level shifter for converting an output signal of the shift register into a swing width suitable for TFT driving of the liquid crystal cell, an output buffer, and the like. The gate driver 13 is composed of a plurality of gate drive integrated circuits and sequentially supplies gate pulses (or scan pulses) having a pulse width of approximately one horizontal period to the gate lines 15.

The power supply unit 40 includes a high potential power voltage VDD, a low potential power voltage VSS, a common voltage Vcom between the high potential power voltage VDD and the low potential power voltage VSS, and a high potential voltage of a gate pulse. (Gate high voltage, Vgh) and gate pulse low voltage (Vlh). The power supply unit 40 may be implemented as a DC-DC converter.

The gamma correction unit 41 generates analog gamma compensation reference voltages GMA1 to GMAn. The analog gamma compensation reference voltages (GMA1 to GMAn) are the positive analog analog gamma compensation reference voltages divided between the high potential supply voltage (VDD) and the common voltage (Vcom), the common voltage (Vcom) and the low potential supply voltage. Negative analog gamma compensation voltages divided between (VSS). The gamma correction unit 41 adjusts the potentials of the analog gamma compensation reference voltages GMA1 to GMAn in accordance with the display position and gradation of the data under the control of the timing controller 11. For example, the gamma correction unit 41 according to the first embodiment of the present invention described below lowers the analog gamma compensation reference voltage of the data to be displayed on the bright line compared to that of the data to be displayed between the bright lines. On the other hand, the gamma correction unit 41 according to the second embodiment of the present invention to increase the analog gamma compensation reference voltage of the data to be displayed between the bright lines compared to that of the data to be displayed on the bright lines. As a result, the gamma correction unit 41 varies the gamma compensation value according to the display position of the data, and further adjusts the gamma compensation value according to the gray level of the data in consideration of the degree of perception of the bright line according to the gray level of the data.

The timing controller 11 receives digital video data RGB and timing signals Vsync, Hsync, DE, and CLK input from an external video source, and supplies the digital video data RGB to the source driver 12 and receives the timing. Based on the signals Vsync, Hsync, DE, and CLK, timing control signals for controlling the operation timing of the source driver 12 and the gate driver 13 are generated. In addition, the timing controller 11 analyzes the digital video data of the input image and generates a dimming signal DIM. The timing controller 11 also generates a gamma correction control signal Cm for selectively adjusting the gamma compensation reference voltages GMA1 to GMAn supplied to the source driver 12. The gamma correction unit 41 adjusts the potentials of the analog gamma compensation reference voltages GMA1 to GMAn in response to the gamma correction control signal Cm from the timing controller 11.

4 is a diagram schematically showing an example of the bright line BL. As shown in FIG. 4, the bright lines BL appear at regular intervals because the lamps 31 are arranged at regular intervals. And the bright line BL appears brighter than the normal display surface between the lamps 31.

In the liquid crystal display and the gamma correction method according to the first embodiment of the present invention, when the image is displayed on the display surface corresponding to the bright line, the gamma compensation reference voltage (GMA1 to GMAn) of the image is converted to low and the bright lines It is possible to uniformly compensate for the luminance of the relatively dark display surface therebetween. In addition, the liquid crystal display and the gamma correction method according to the second embodiment of the present invention convert the gamma compensation reference voltages GMA1 to GMAn of the image to a high level when the image is displayed on the display surface between the lines. It is possible to uniformly compensate for the luminance of the relatively dark display surface. Hereinafter, the liquid crystal display according to the first embodiment of the present invention and a gamma correction method thereof will be described.

5 shows in detail a circuit section for generating a gamma correction control signal in the timing controller 11.

1 and 5, the timing controller 11 includes an option terminal Opt, a gray scale determination unit 51, a display position determination unit 52, a gamma correction control signal generator 53, and a memory 54. And a selector 55.

The option terminal Opt may be connected to the power supply voltage Vcc of the high logic voltage by a set maker or to the ground voltage GND of the low logic voltage through a pull-down resistor. For example, the set maker may selectively correct the gamma compensation reference voltages GMA1 to GMAn by applying a power supply voltage Vcc to the option terminal Opt, and apply a ground voltage GND to the option terminal Opt. The gamma compensation reference voltages GMA1 to GMAn may not be corrected. Therefore, the set maker may select whether or not to correct the gamma compensation reference voltage according to the bright line inspection result and the panel using the option terminal Opt formed in the timing controller 11.

The gray scale determination unit 51 reads the digital video data RGB and determines which gray scale range the digital video data RGB to be currently displayed on the liquid crystal display panel 10 belongs to. The gray scale determination result of the gray scale determination unit 51 is supplied to the gamma correction control signal generator 53.

The display position determiner 52 receives the vertical synchronous signal Vsync and the horizontal synchronous signal Hsync, counts the horizontal synchronous signal Hsync every frame, and then displays the digital video data to be displayed on the liquid crystal display panel 10. RGB) display position is determined. The vertical synchronization signal Vsync is generated in one frame period to indicate one frame period. The horizontal synchronization signal Hsync is generated in a scan time period of one horizontal line in the liquid crystal display panel to indicate one horizontal period. Therefore, the display position determining unit 52 resets the count value every frame period in accordance with the vertical synchronization signal Vsync. The horizontal synchronization signal Hsync indicates a display line in which valid data exists and may be replaced by a data enable signal DE generated in one horizontal period. The display position determination result of the display position determination unit 56 is supplied to the gamma correction control signal generation unit 53.

The gamma correction control signal generator 53 generates a control signal C2 in accordance with the gray scale determination result from the gray scale determination unit 51 and the display position determination result from the display position determination unit 52. To this end, the gamma correction control signal generator 53 selects a gamma compensation value from a look-up table stored in the memory 54 using the gray scale determination result and the display position determination result as read addresses. The control signal C2 corresponding to the gamma compensation value is output.

In the lookup table of the memory 54, gamma compensation values and position information of the bright lines which are different depending on the gray scale are listed. The gamma compensation value and position information of the bright line may be obtained through the bright line inspection performed after the liquid crystal display panel 10 and the backlight unit 20 are assembled. In other words, a gamma compensation value for each gray level, such as a gamma compensation value in the low gradation range, a gamma compensation value in the mid gradation range, and a gamma compensation value in the high gradation range, and position information of the bright line are listed in the lookup table. The gamma compensation value in the midtone range is higher than the gamma compensation value in the low tonal range and the gamma compensation value in the high tonal range. Since the information listed in the lookup table is hardly recognized in the high gradation, the gamma compensation value of the high gradation may be omitted. Depending on the model of the panel, the driving characteristics, or the type or number of lamps, the shape, spacing, and luminance of the bright lines may vary. Therefore, the memory 54 is preferably EEPROM (electrically erasable and programmable read only memory) to adjust the gamma compensation value and position information of the bright line.

For example, the gamma correction control signal generation unit 53 performs the intermediate gray level if the display position of the currently displayed image is present in the display surface of the bright line BL and the gray level of the digital video data RGB of the image falls within the intermediate gray range. A gamma compensation value of a range is selected and a control signal C2 corresponding to the gamma compensation value is output. In addition, the gamma correction control signal generation unit 53 performs the low gray scale range if the display position of the currently displayed image exists in the display surface of the bright line BL, and the gray scale of the digital video data RGB of the image belongs to the low gray scale range. Selects a gamma compensation value and outputs a gamma correction control signal C2 corresponding to the gamma compensation value.

The selector 55 selects either the control signal C1 in the non-gamma correction mode or the control signal C2 from the gamma correction control signal generator 53 according to the option signal from the option terminal Opt. . The control signal C1 in the non-gamma correction mode may be generated in the timing controller 11 or may be generated outside the timing controller 11 and input to the timing controller 11. The timing controller 11 operates in the gamma correction mode when the option signal is high logic, while the timing controller 11 operates in the non-gamma correction mode when the option signal is low logic. ) Outputs the control signal C2 from the gamma correction control signal generator 53 as a gamma correction control signal Cm, and when the option signal is "0", the selector 55 controls the control signal in the non-gamma correction mode. (C1) is output as a gamma correction control signal (Cm). The gamma correction control signal Cm output from the selector 55 is input to the control terminal of the gamma correction unit 41 to control the gamma correction unit 41. The selector 55 may be implemented as a multiplexer.

6 shows the gamma correction unit 41 in detail. 7 schematically shows a gamma correction method of a liquid crystal display according to a first embodiment of the present invention.

6 and 7, the gamma corrector 41 includes a power supply adjuster 65, a first divided circuit 61, a second divided circuit 62, and a first selector 63.

The power regulator 65 may include a plurality of power regulators 651 to 653 connected in parallel to the high potential power voltage source VDD, and a second one for connecting any one of the power regulators 651 to 653 to the output terminal. And a selector 66. Each of the power adjusters 651 to 653 generates different corrected high potential power voltages by dropping the high potential power voltage VDD to different resistance values. To this end, the power adjusters 651 to 653 include resistors having different resistance values. The resistance value of the second power adjuster 652 is higher than the resistance of each of the other power adjusters 651 and 653. The second power adjuster 652 drops the high potential power voltage VDD to generate an optimized corrected high potential power voltage VDD2 when the image to be displayed on the bright line is data belonging to the halftone range. The resistance of the first power adjuster 651 is lower than the resistance of the second power adjusters 652 and higher than the resistance of the third power adjuster 653. The first power adjuster 651 may drop the high potential power voltage VDD to generate an optimized corrected high potential power voltage VDD1 when the image to be displayed on the bright line is data falling within the low gray scale range. The resistance value of the third power source adjustment unit 653 is lower than the resistance value of each of the other power source adjustment units 651 to 653. The third power adjuster 653 may drop the high potential power voltage VDD to generate an optimized high potential power voltage VDD3 when the image to be displayed on the bright line is data belonging to a high gradation range. As a result, the second corrected high potential power voltage VDD2 dropped by the second power adjuster 652 is the first and third corrected high potentials dropped by the first and third power adjusters 651 and 653. It is lower than the voltage voltages VDD1 and VDD3. In addition, the first corrected high potential power voltage VDD1 dropped by the first power adjuster 651 is a voltage between the second corrected high potential power voltage VDD2 and the third corrected high potential power voltage VDD3. . Since the bright lines are hardly visible at high gradations, the third power supply adjusting unit 653 can be omitted.

The second selector 66 selects one of the first to third corrected high potential power voltages VDD1 to VDD3 in response to the gamma correction control signal Cm.

The first voltage divider circuit 61 includes a plurality of resistors R1 to Rn connected in series between the high potential power voltage source VDD and the low potential voltage source VSS. Output nodes are formed between the resistors R1 to Rn. The first voltage dividing circuit 61 divides the high potential power voltage VDD from the power supply unit 40 to generate a plurality of first gamma compensation reference voltages.

The second voltage dividing circuit 62 includes a plurality of resistors R1 connected in series between the corrected high potential power voltage source VDD 'and the low potential voltage source VSS from the second selector 66 of the power adjuster 65. 'To Rn'). Output nodes are formed between the resistors R1 'through Rn'. The second divider circuit 62 divides the corrected high potential power voltage source VDD 'from the second selector 66 of the power adjuster 65 to generate a plurality of second gamma compensation reference voltages.

The first selector 63 supplies the first gamma compensation reference voltages generated by the first voltage dividing circuit 61 to the source driver 12 in response to the gamma correction control signal Cm, or the second voltage dividing circuit ( The second gamma compensation reference voltages generated by 62 are supplied to the source driver 12. To this end, the first selector 63 includes switches SW for selecting gamma compensation reference voltages output from the first and second voltage dividing circuits 61 according to the gamma correction control signal Cm.

When the non-gamma correction mode is selected by the option terminal Opt or an image to be displayed on the display surface N between the bright lines BL is input, the gamma correction control signal Cm is set to "000" and the gamma correction mode is set. Inputs the gamma correction control signal Cm when the low gray scale image to be displayed on the bright lines BL is input to " 101 ", and enters the middle gray scale image to be displayed on the bright lines BL in the gamma correction mode. Is 110 when the gamma correction control signal Cm is input, and the gamma correction control signal Cm when the high gradation range image to be displayed on the bright lines BL in the gamma correction mode is input. The operation of the gamma correction unit 41 will now be described.

When the non-gamma correction mode is selected or an image to be displayed on the display surface N between the bright lines BL is input, the timing controller 11 generates the gamma correction control signal Cm as "000". Then, the first selector 63 of the gamma correction unit 41 generates a first gamma generated from the first voltage divider 61 in response to "0" of the first bit, which is the most significant bit of the gamma correction control signal Cm. The compensation reference voltages are supplied to the source driver 12.

When the image of the low gradation range to be displayed on the bright lines BL in the gamma correction mode is input, the timing controller 11 generates a gamma correction control signal Cm as "101". Then, the second selector 66 of the gamma correction unit 41 generates the second corrected high potential power voltage VDD1 in response to "01", which is the second and third bits of the gamma correction control signal Cm. The voltage is supplied to the voltage dividing circuit 62. The first selector 63 of the gamma corrector 41 generates a second gamma generated from the second voltage divider 62 in response to "1" of the first bit, which is the most significant bit of the gamma correction control signal Cm. The compensation reference voltages are supplied to the source driver 12.

When the image of the halftone range to be displayed on the bright lines BL in the gamma correction mode is input, the timing controller 11 generates a gamma correction control signal Cm as “110”. Then, the second selector 66 of the gamma correction unit 41 generates the second corrected high potential power voltage VDD2 in response to the second and third bits "10" of the gamma correction control signal Cm. The voltage is supplied to the voltage dividing circuit 62. The first selector 63 of the gamma corrector 41 generates a second gamma generated from the second voltage divider 62 in response to "1" of the first bit, which is the most significant bit of the gamma correction control signal Cm. The compensation reference voltages are supplied to the source driver 12.

When the image of the high gradation range to be displayed on the bright lines BL in the gamma correction mode is input, the timing controller 11 generates the gamma correction control signal Cm as “111”. Then, the second selector 66 of the gamma correction unit 41 supplies the third corrected high potential power voltage VDD3 in response to "11" which is the second and third bits of the gamma correction control signal Cm. The voltage is supplied to the voltage dividing circuit 62. The first selector 63 of the gamma corrector 41 generates a second gamma generated from the second voltage divider 62 in response to "1" of the first bit, which is the most significant bit of the gamma correction control signal Cm. The compensation reference voltages are supplied to the source driver 12.

As a result, in the gamma correction method of the liquid crystal display according to the first exemplary embodiment of the present invention, the gamma compensation reference voltages GMA1 to the image to be displayed on the bright line BL by dividing the corrected high potential power voltage VDD '. By correcting only GMAn, the corrected gamma compensation reference voltages GMA1 to GMAn are supplied to the source driver 12.

In the liquid crystal display and the gamma correction method according to the second exemplary embodiment of the present invention, when an image is displayed on the display surface N between the bright lines BL as shown in FIG. 8, the gamma compensation reference voltages GMA1 to GMA of the image are displayed. GMAn is corrected high to uniformly compensate for the luminance of the bright lines BL and the relatively dark display surface N therebetween. To this end, the timing controller 11 activates the gamma correction control signal Cm only when an image to be displayed on the display surface N having a relatively low luminance located between the bright lines BL is input. In FIG. 6, the power adjuster 65 increases the potential of the high potential power voltage VDD by using a level shifter or a booster circuit. In this second embodiment, the first selector 63 is positioned between the bright lines BL in response to the gamma correction control signal Cm to input an image to be displayed on the display surface N having a relatively low luminance. The output of the second voltage dividing circuit 62 is selected as the gamma compensation reference voltages GMA1 to GMAn and supplied to the source driver 12.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the 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.

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

2 is a perspective view showing in detail the structure of the backlight unit shown in FIG.

3 is a cross-sectional view of the backlight unit shown in FIG.

4 is a diagram schematically showing an example of a bright line.

FIG. 5 is a block diagram illustrating in detail a circuit unit generating a gamma correction control signal in the timing controller shown in FIG. 1; FIG.

FIG. 6 is a circuit diagram illustrating in detail a gamma correction unit illustrated in FIG. 1.

7 is a view illustrating a gamma correction method of a liquid crystal display according to a first embodiment of the present invention.

8 is a diagram illustrating a gamma correction method of a liquid crystal display according to a second exemplary embodiment of the present invention.

Description of the Related Art

10 liquid crystal display panel 12 source driver

13 gate driver 20 backlight unit

21: backlight driver 40: power supply

41: gamma correction unit 51: gray scale determination unit

52: display position determination unit 53: gamma correction control signal generator

54: memory 55, 63, 66: selection

61, 62: voltage divider circuit 65: power supply control unit

Claims (12)

A liquid crystal display panel in which a plurality of data lines and a plurality of gate lines intersect and liquid crystal cells are arranged in a matrix; A plurality of light sources for irradiating light onto the liquid crystal display panel; A source driver converting digital video data into an analog data voltage based on a gamma compensation voltage and supplying the digital video data to the data lines; A gate driver sequentially supplying a gate pulse to the gate lines; And Generating gamma compensation voltages of the first display surfaces of the liquid crystal display panel at positions opposite to the light sources, and gamma compensation voltages of the second display surfaces of the liquid crystal display panel between the first display surfaces. Equipped with a gamma correction unit, A gamma compensation voltage of the first display surfaces and a gamma compensation voltage of the second display surfaces are different from each other, The gamma correction unit, And if the gradation of the digital video data is an intermediate gradation, the correction width of the gamma compensation voltage is increased as compared with a low gradation and a high gradation. delete The method of claim 1, And a timing controller generating a control signal for controlling the gamma correction unit and controlling operation timings of the source driver and the gate driver. The method of claim 3, wherein The timing controller includes: An option terminal configured to receive one of a high logic voltage and a low logic voltage to generate an option signal; A gray scale determination unit configured to analyze digital video data of an input image and determine a gray scale of the digital video data; A display position determining unit which determines a display position of the digital video data based on an input timing signal; A memory storing a lookup table having a gamma compensation value determined according to a gray level of the digital video data; A gamma correction control signal generator for generating a control signal of a gamma correction mode by selecting the gamma compensation value from the lookup table according to the output of the gray scale determination unit and the display position determination unit; And And a selector which selects one of a control signal in a non-gamma correction mode and a control signal in the gamma correction mode according to the option signal to generate the control signal. delete 5. The method of claim 4, The gamma correction unit, A first voltage dividing circuit for dividing the first power supply voltage; A second voltage dividing circuit for dividing a second power voltage different from the first power voltage; A first selector configured to select one of an output of the first voltage divider circuit and an output of the second voltage divider circuit in response to the control signal to generate the gamma compensation voltage; A power adjuster configured to correct the first power voltage by different correction widths according to the gray levels to generate a plurality of corrected power voltages separated by gray levels; And And a second selector configured to select one of the corrected power supply voltages and generate the second power supply voltage in response to the control signal. A plurality of data lines and a plurality of gate lines intersect and liquid crystal cells are arranged in a matrix form, a plurality of light sources for irradiating light to the liquid crystal display panel, and digital video data based on gamma compensation voltage. A gamma correction method of a liquid crystal display including a source driver converting an analog data voltage to supply the data lines, a gate driver sequentially supplying a gate pulse to the gate lines, and a gamma correction unit generating the gamma compensation voltage. To Inspecting a luminance difference between first display surfaces of the liquid crystal display panel corresponding to the light sources and second display surfaces positioned between the first display surfaces; Controlling a gamma compensation voltage output from the gamma compensation unit to a gamma compensation voltage of the first display surface and a gamma compensation voltage of the second display surface; And If the gray level of the input image is a middle gray level, increasing the correction width of the gamma compensation voltage compared to the low gray level and high gray level; A gamma compensation voltage of the first display surfaces and a gamma compensation voltage of the second display surfaces are different from each other. The method of claim 7, wherein The checking of the luminance difference between the first display surfaces of the liquid crystal display panel corresponding to the light sources and the second display surfaces positioned between the first display surfaces may include: And checking the luminance difference between the first display surfaces and the second display surfaces according to the gray level of the image. delete 9. The method of claim 8, Receiving an option signal through an option terminal; Analyzing the digital video data of the input image to determine the gray level of the digital video data; Determining a display position of the digital video data based on an input timing signal; Storing a lookup table having a gamma compensation value determined according to a gray value of the digital video data in a memory; Generating a control signal of a gamma correction mode by selecting the gamma compensation value from the lookup table according to the gray level determination result and the display position determination result; Selecting one of a control signal of a non-gamma correction mode and a control signal of the gamma correction mode according to the option signal to generate a control signal; And And applying the control signal to the gamma correction unit to control the gamma compensation voltage. delete 11. The method of claim 10, Correcting the potential of the gamma compensation voltage, Generating a first gamma compensation voltage by dividing the first power supply voltage; Generating a second gamma compensation voltage by dividing a second power supply voltage different from the first power supply voltage; Selecting one of the first gamma compensation voltage and the second gamma compensation voltage according to the control signal; Correcting the first power voltage by a different correction width according to the gray level to generate a plurality of corrected power voltages separated for each gray level; And And selecting one of the corrected power supply voltages according to the control signal to generate the second power supply voltage.

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