KR101604493B1 - Liquid crystal display and driving method of thereof - Google Patents

Abstract

The present invention relates to a liquid crystal display device and a driving method thereof that can improve a contrast ratio of a display image.

The liquid crystal display device includes: a liquid crystal display panel displaying image data; A backlight unit that includes a plurality of light sources and divides the surface light source irradiated to the liquid crystal display panel into blocks of a matrix type; A backlight driving circuit for driving the light sources on a block basis based on a block-by-block PWM signal for controlling lighting; And a controller for analyzing the image data in units of blocks and calculating a weight inversely proportional to an average luminance value of image data to be displayed in neighboring blocks which is proportional to a maximum luminance value of image data to be displayed in the corresponding block, And a backlight control circuit for independently adjusting the dimming duty of the PWM signal of the corresponding block with reference to a constant.

Description

TECHNICAL FIELD [0001] The present invention relates to a liquid crystal display (LCD)

The present invention relates to a liquid crystal display device and a driving method thereof that can improve a contrast ratio of a display image.

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 liquid crystal display device displays an image using a thin film transistor (hereinafter referred to as "TFT") as a switching element. A transmissive liquid crystal display device that occupies most of the liquid crystal display device displays an image by controlling an electric field applied to the liquid crystal layer to modulate light incident from the backlight unit.

The image quality of the liquid crystal display device depends on the contrast characteristics. The method of modulating the light transmittance of the liquid crystal layer by controlling the data voltage applied to the liquid crystal layer limits the improvement of the contrast characteristic. In order to improve the contrast characteristic, an AFLC (Area Focused Luminance Cortrollable) technique for adjusting the luminance of the backlight unit according to an image has been proposed.

The AFLC technique divides an image displayed on one screen into a predetermined number of logical blocks and adjusts the brightness of backlights (light sources) corresponding to the blocks according to an average luminance value to be displayed by the data signal corresponding to each block. The AFLC technique analyzes an image of one frame in a predetermined number of blocks, increases the backlight luminance of a block having a large average luminance value, and decreases the backlight luminance of a block having a small average luminance value . The AFLC technique improves contrast characteristics and reduces power consumption by locally varying brightness according to an input image.

However, since the AFCL technique uses only the average luminance value of the corresponding block when determining the luminance of the backlight of each block, it is difficult to improve the contrast characteristic when a dark region and a bright region exist in the block. For example, when an image with a star in the night sky is mostly dark and a very bright area near white is partially present, the average brightness value of the image data is set to be very small, so that the brightness of the backlight of the block is low do. As a result, the bright region is displayed very dark, and the contrast ratio of the block is reduced.

The backlight of each block not only affects the brightness of the block but also affects the brightness of the neighboring block by about 20%. The AFCL technique determines the brightness of the backlight without considering the influence of the light leakage between these neighboring blocks, so there is a limit to improve the contrast ratio.

Accordingly, it is an object of the present invention to provide a liquid crystal display device and a driving method thereof that can improve a contrast ratio of a display image.

According to an aspect of the present invention, there is provided a liquid crystal display device including: a liquid crystal display panel displaying image data; A backlight unit that includes a plurality of light sources and divides the surface light source irradiated to the liquid crystal display panel into blocks of a matrix type; A backlight driving circuit for driving the light sources on a block basis based on a block-by-block PWM signal for controlling lighting; And a controller for analyzing the image data in units of blocks and calculating a weight inversely proportional to an average luminance value of image data to be displayed in neighboring blocks which is proportional to a maximum luminance value of image data to be displayed in the corresponding block, And a backlight control circuit for independently adjusting the dimming duty of the PWM signal of the corresponding block with reference to a constant.

The backlight control circuit adjusts the dimming duty of the PWM signal of the corresponding block by comparing the amount of the clapping amount of the corresponding block multiplied by the weighting constant with the amount of the corresponding block.

The amount of the clapping is obtained by multiplying a clipping error corresponding to the brightness reduction of the light sources due to the local dimming in the corresponding block, by the histogram value by the gradation of the image data.

The amount of the leakage is obtained by multiplying the luminance difference corresponding to the brightness change of the corresponding block according to the brightness of the neighboring blocks by the histogram value of the image data in the local dimming.

The backlight control circuit determines a dimming duty of the PWM signal of the corresponding block by the dimming duty when the amount of clapping of the corresponding block is multiplied by the weighting constant and the amount of the leakage of the corresponding block is equal to each other.

Wherein the backlight control circuit comprises: a histogram analyzer for analyzing the image data and calculating a histogram value for each gradation; An error calculating unit for calculating a clipping amount and a leakage amount for each block after dimming according to a feedback dimming control signal; A luminance calculation unit for analyzing the image data and calculating an average luminance value and a maximum luminance value for each block; A weighting constant calculating unit for calculating the weighting coefficient for each block; A dimming control unit for comparing a quantity obtained by multiplying the amount of clamping by the weighting constant and a quantity of the leaky amount in each of the blocks to adjust a dimming duty of the dimming control signal for each block; And a PWM generator for generating the PWM signal according to the optimum dimming duty for each block.

Wherein the dimming control unit adjusts a dimming control signal of the corresponding block so that the dimming duty is reduced by a predetermined value if the amount of the reakage is greater than the multiplied amount in the corresponding block, To the error calculator.

Wherein the dimming control unit adjusts a dimming control signal of the corresponding block so that the dimming duty is increased by a predetermined value when the amount of the leakage is smaller than the multiplied amount, And feeds back the signal to the error calculating section.

The dimming control unit determines the dimming duty cycle as the optimum dimming duty cycle when the feedback amount and the amount multiplied by the feedback amount in the corresponding block become equal to each other.

A liquid crystal display panel in which image data is displayed according to an embodiment of the present invention; and a liquid crystal display device having a backlight unit including a plurality of light sources and dividing a surface light source irradiated on the liquid crystal display panel into blocks of matrix type The method includes: (A1) driving light sources on a block-by-block basis based on a block-by-block PWM signal for controlling a turn-off; And a controller for analyzing the image data in units of blocks and calculating a weight inversely proportional to an average luminance value of image data to be displayed in neighboring blocks which is proportional to a maximum luminance value of image data to be displayed in the corresponding block, (A2) independently adjusting the dimming duty of the PWM signal of the corresponding block with reference to a constant.

A liquid crystal display device and a driving method thereof according to the present invention divide a display image into a predetermined number of logical blocks and calculate a clipping amount and a leakage amount of each block in proportion to a maximum luminance value of each block and an average luminance value And then the light sources of the corresponding block are driven with the dimming duty when the amount of the clapping of the block is multiplied by the corresponding weighting constant and the amount of the memory of the corresponding block becomes equal to each other. As a result, in the liquid crystal display device and the driving method thereof according to the present invention, the brightness of the high-luminance data can be compensated even in the block having the low average luminance value, thereby ensuring a high contrast ratio.

Hereinafter, preferred embodiments of the present invention will be described with reference to FIGS. 1 to 7. FIG.

1 shows a liquid crystal display according to an embodiment of the present invention.

1, a liquid crystal display according to an exemplary embodiment of the present invention includes a liquid crystal display panel 10, a data driving circuit 12 for driving data lines DL of the liquid crystal display panel 10, A gate driving circuit 13 for driving the gate lines GL of the panel 10, a timing controller 11 for controlling the data driving circuit 12 and the gate driving circuit 13, a liquid crystal display panel 10, A backlight driving circuit 15 for driving the light sources of the backlight unit 16 and a backlight unit 15 for analyzing the input image and controlling the backlight driving circuit 15 according to the analysis result, And a control circuit (14).

The liquid crystal display panel 10 includes two glass substrates and a liquid crystal layer formed therebetween. A plurality of data lines DL and a plurality of gate lines GL are intersected with each other on a lower glass substrate of the liquid crystal display panel 10. [ The liquid crystal cells Clc are arranged in a matrix form in the liquid crystal display panel 10 by the intersection structure of the data lines DL and the gate lines GL. A TFT, a pixel electrode 1 of a liquid crystal cell Clc connected to the TFT, and a storage capacitor Cst are formed on the lower glass substrate of the liquid crystal display panel 10.

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 data driving circuit 12 includes a plurality of data drive ICs. The data drive integrated circuit includes a shift register for sampling a clock signal, a register for temporarily storing digital image data (RGB), a data register for storing one line of data in response to a clock signal from a shift register, A digital / analog converter for selecting a positive / negative gamma voltage under reference to a gamma reference voltage corresponding to a digital data value from a latch and latch for outputting simultaneously, an analog / digital converter converted by a positive / negative gamma voltage, A multiplexer for selecting a data line DL to which data is supplied, and an output buffer connected between the multiplexer and the data line DL. The data driving circuit 12 latches the digital image data RGB under the control of the timing controller 11 and outputs the latched digital image data RGB to the positive polarity / Polarity analog data voltage, and supplies it to the data lines DL.

The gate drive circuit 13 includes a plurality of gate drive integrated circuits. The gate drive integrated circuit 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, and an output buffer. The gate drive circuit 13 sequentially outputs a scan pulse (or a gate pulse) under the control of the timing controller 11 and supplies it to the gate lines GL to select a horizontal line to which the data voltage is to be applied.

The timing controller 11 rearranges the digital image data RGB input from the system board on which the external video source is mounted according to the resolution of the liquid crystal display panel 10 and supplies it to the backlight control circuit 14. [ Then, digital image data (RGB) fed back from the backlight control circuit 14 is supplied to the data driving circuit 12.

The timing controller 11 generates timing control signals for controlling the operation timings of the data driving circuit 12 and the gate driving circuit 13 based on the timing signals Vsync, Hsync, DE, DCLK from the system board DDC, GDC). The timing controller 11 inserts an interpolation frame between the frames of the input video signal input at a frame frequency of 60 Hz and multiplies the data timing control signal DDC and the gate timing control signal GDC to obtain 60 × N The operation of the data driving circuit 12 and the gate driving circuit 13 can be controlled with a frame frequency of Hz or more.

The backlight unit 16 includes a plurality of light sources to divide the surface light source irradiated on the liquid crystal display panel 10 into blocks of a matrix form. The backlight unit 16 may be implemented as either a direct type or an edge type. Although the backlight unit shown in Fig. 1 exemplifies a direct-type backlight unit, the backlight unit of the present invention is not limited to the direct-type backlight unit but may include any known backlight unit. The direct-type backlight unit 16 has a structure in which a plurality of optical sheets and a diffusion plate are stacked under the liquid crystal display panel 10, and a plurality of light sources are disposed under the diffusion plate. The light sources may be realized by point light sources such as a light emitting diode (LED). The optical sheets include at least one prism sheet and at least one diffusing sheet to diffuse the light incident from the diffusing plate and refract the path of light at an angle substantially perpendicular to the light incident surface of the liquid crystal display panel. The optical sheets may include a dual brightness enhancement film (DBEF).

The backlight driving circuit 15 drives the light sources on a block-by-block basis based on a pulse width modulation (PWM) signal for each block for controlling the lighting. The digital image data (RGB) displayed on one screen can be divided into a predetermined number of logical units in accordance with the number of division of the surface light sources. For example, the digital image data RGB of one frame may be divided into a plurality of blocks BLK [1,1] to BLK [n, m] as shown in FIG.

The backlight control circuit 14 analyzes input image data RGB on a block-by-block basis under the control of the timing controller 11 and adjusts the duty of the PWM signal on a block-by-block basis according to the analysis result. The backlight control circuit 14 can enlarge the dynamic range of the input image data (RGB) to compensate for the reduced brightness due to the dimming duty ratio adjustment. The backlight control circuit 14 calculates the optimal luminance value of each block in consideration of the maximum luminance value of the image data to be displayed in each corresponding block and the average luminance value of the image data to be displayed in neighboring blocks that affect the brightness of the corresponding block Deriving the dimming duty and locally adjusting the brightness of the light sources based thereon.

3 shows the backlight control circuit 14 in detail.

3, the backlight control circuit 14 includes a histogram analyzer 141, an error calculator 142, a brightness calculator 143, an upper weight calculator 144, a dimming controller 145, And a PWM generator 146. [

The histogram analyzing unit 141 receives the image data RGB in units of one frame, calculates a histogram of the gradation of the image data RGB corresponding to each block, and supplies the histogram of each gradation to the error calculating unit.

The error calculator 142 dims according to the dimming control signal fed back from the dimming control unit 145, and calculates a clipping amount and a leaking amount in each corresponding block.

For this purpose, the error calculator 142 previously stores a target luminance value (refer to "Yideal" in FIG. 4) to be output according to the gradation of the image data RGB as shown in FIG. 4, Then calculate the clipping error caused by the decrease in maximum brightness and the leakage error caused by the light leakage phenomenon.

When the brightness of the light sources is reduced due to local dimming (see "After Dimming" in FIG. 4), the brightness of light that can be maximized in the corresponding block decreases. In this case, in order to compensate for the reduced brightness and to match the target luminance value, the error calculating unit 142 can enlarge the dynamic range of the image data (RGB) through data modulation. However, even if the image data (RGB) is modulated, the brightness of the light in the corresponding block is difficult to achieve the target brightness due to the tonal bunching or the like at a relatively high tone. In other words, in FIG. 4, the target luminance value is clipped (indicated by a solid line) to a constant value lower than the maximum luminance value in the high gradation period. The clipping error e _c (g, d _{i , j} ) for each block due to the clipping phenomenon is obtained by the following equation (1).

In Equation 1, "g" represents the gradation level, "d _{i , j} " represents the dimming value of the (i, j) th block, and "γ" represents the gamma value (eg 2.2).

On the other hand, at the time of local dimming with respect to the light sources, at a relatively low gradation, as shown in FIG. 4, the brightness is higher than the target brightness in the corresponding block. This is because the liquid crystal layer does not completely block the light, and the brightness of the corresponding block is influenced by the brightness of neighboring blocks. This light leakage phenomenon is called light leakage, and the leakage error per block is obtained by the following equation (2).

In Equation (2), "g" represents a gradation level, "d _{i , j} " represents a dimming value of the (i, j) th block, and "γ" represents a gamma value (eg 2.2).

In this block, when the brightness of the light sources is reduced, the light leakage phenomenon is improved, but the clipping phenomenon becomes conspicuous. On the other hand, if the brightness of the light sources is increased, the clipping phenomenon is improved, but the light leakage phenomenon becomes conspicuous. Therefore, it is important to find the dimming duty that can appropriately adjust the amount of clipping and the amount of leaking in the block.

To this end, the error calculator 142 calculates the clipping amount D _c (i, j) for each block by multiplying the clipping error by the histogram value for each gradation from the histogram analyzer 141 as shown in Equation 3 below.

In Equation (3), n (g) represents the number of pixels having the gradation level g as a histogram analysis value by gradation.

The error calculator 142 calculates the amount of knowledge (D _j (i, j)) per block by multiplying the logarithmic error by the histogram value by the histogram from the histogram analyzer 141 as shown in Equation 4 below .

In Equation (4), n (g) represents the number of pixels having the gradation level g as a histogram analysis value by gradation.

The luminance calculator 143 receives the image data RGB in units of one frame, calculates the average luminance value and the maximum luminance value of the image data RGB corresponding to each block, and calculates an average luminance value and a maximum luminance value And supplies the value to the weight calculation upper part 144. [

The weighting upper calculator 144 calculates a weighting coefficient determined by a function in proportion to the maximum luminance value of the block and inversely proportional to the average luminance value of the neighboring blocks on a block by block basis. (i, j) weighted constant (α _{i, j)} th block is obtained from the equation (5) below.

In Equation (5), " MAX (i, j) "represents the maximum luminance value of the (i, j) th block and" APL (I, j) th block and the neighboring blocks (i, j) th block, the average luminance value of the (i, j) And the horizontal and vertical sizes of the block, respectively. Here, the size "M" of the macroblock may be predetermined to a predetermined value according to the number (a, b) of neighboring blocks that affect the brightness of the (i, j) th block as shown in FIG. In Equation (5), the denominator represents an average luminance value of neighboring blocks.

5, the weighting constant of the block is determined to be proportional to the maximum luminance value of the block and inversely proportional to the average luminance value of the neighboring blocks. Even if the average luminance value of the block is very low, such as when a star shines in a dark night sky, there may be a very bright region in it. In this case, if the brightness of the light sources of the block is decreased according to the average luminance value as in the conventional case, the problem of the star disappears. Accordingly, the weight constant of the block is determined as a value proportional to the maximum luminance value of the block, thereby compensating for the brightness of the high luminance data in the block having the low average luminance value.

Also, if the neighboring blocks are bright due to the influence of the light leakage caused by the neighboring blocks, the corresponding block becomes bright by a certain ratio. Therefore, the weight constant of the block is determined to be inversely proportional to the average luminance value of neighboring blocks, thereby reducing the degree of light leakage by neighboring blocks.

The dimming control unit 145 controls the dimming duty of the dimming control signal using the amount of clipping and the amount of clipping for each block from the error calculating unit 142 and the weighting coefficient for each block from the weighting upper calculating unit 144 . The dimming control unit 145 compares the amount by which the amount of clapping of the block is multiplied by the weighting constant of the block and the amount of the leak of the block. The dimming control unit 145 adjusts the dimming control signal of the corresponding block so that the dimming duty is reduced by a predetermined value, and then outputs the adjusted dimming control signal to the error calculation (142). On the other hand, if the amount of the leakage is smaller than the multiplied amount, the dimming control unit 145 adjusts the dimming control signal of the corresponding block so that the dimming duty is increased by a predetermined value, And feeds it back to the calculation unit 142. When the multiplication amount and the amount of the leaky are equal to each other through the feedback process, the dimming control unit 145 determines the dimming duty at that time as the optimum dimming duty, and supplies the dimming control signal including the optimum dimming duty to the PWM generator 146).

The PWM generator 146 generates a PWM signal having the optimum dimming duty in response to the dimming control signal from the dimming controller 145. [

FIG. 6 shows experimental results comparing the effects of the present invention with the prior art.

6A is a display image when all the light sources of the backlight unit are turned on irrespective of the image data, and the light leakage is severe in the entire area of the screen, and the contrast characteristic of the display image is very bad. FIG. 6 (b) is a display image obtained by adjusting the luminance of the light sources according to the average luminance value of each block by applying the conventional AFLC technique. As a result, stars hardly appear due to clipping problem, making detailed image representation difficult. FIG. 6C shows a display image when luminance of the light sources is adjusted in accordance with the maximum luminance value of each block, in which the light is still generated at the portion where the stars are displayed, and the contrast characteristic is bad.

6 (d) is a display image according to the present invention, in which the luminance of each block is adjusted by using a weighting constant determined in proportion to the maximum luminance value of the block and inversely proportional to the average luminance value of neighboring blocks 6 (c) and 6 (d), it is possible to display a detailed image while having high contrast characteristics, that is, without generating light leakage.

7 illustrates a method of driving a liquid crystal display according to an embodiment of the present invention.

Referring to FIG. 7, in this driving method, when the image data RGB is inputted S1, the input image data RGB are analyzed in units of one frame and the histogram values of the gradation of the image data RGB (S2).

In this driving method, dimming is performed according to the feedback dimming control signal, and the amount of clipping and the amount of leakage in the corresponding block are calculated (S3). Here, the amount of clapping is obtained by multiplying the clipping error corresponding to the brightness reduction of the light sources due to dimming in the corresponding block, by the histogram value by the gradation. The amount of leakage is obtained by multiplying the luminance error corresponding to the brightness change of the corresponding block according to the brightness of neighboring blocks at the time of dimming by the value of the histogram by hierarchy.

In this driving method, the image data (RGB) is input in units of one frame, and the average luminance value and the maximum luminance value of the image data (RGB) corresponding to each block are calculated (S4).

In this driving method, a weighting coefficient determined in a function in proportion to a maximum luminance value of the block and inversely proportional to an average luminance value of neighboring blocks is calculated for each block (S5).

In this driving method, the amount by which the amount of clapping of the block is multiplied by the weighting constant of the block and the amount of the retained amount of the block are compared with each other (S6). If the amount of leakage is greater than the multiplied amount (NO in S6 and S7), the driving method adjusts the dimming control signal so that the dimming duty is reduced by a predetermined value (S8) And feeds the adjusted dimming control signal to the step S3. On the other hand, if the amount of the leakage is smaller than the multiplied amount (NO in S6 and NO in S7), the driving method adjusts the dimming control signal so that the dimming duty is increased by a predetermined value (S9) And feeds the adjusted dimming control signal to the step S3.

If the multiplication amount and the amount of the rekey are equal to each other (S6), the driving method determines the dimming duty at that time as the optimum dimming duty and then adjusts the duty of the PWM signal in accordance with the optimum dimming duty. (S10). By adjusting the duty of the PWM signal, the brightness of the light sources is locally controlled.

As described above, the liquid crystal display and the driving method thereof according to the present invention divide a display image into a predetermined number of logical blocks, and calculate a clipping amount and a leakage amount of each block in proportion to the maximum luminance value of each block, After comparing the weighting factor in inverse proportion to the average luminance value of the blocks, the dimming duty when the amount of the clapping of the block multiplied by the corresponding weighting constant is equal to the amount of the corresponding block, . As a result, in the liquid crystal display device and the driving method thereof according to the present invention, the brightness of the high-luminance data can be compensated even in the block having the low average luminance value, thereby ensuring a high contrast ratio.

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 showing a liquid crystal display device according to an embodiment of the present invention.

Fig. 2 is a diagram showing an example in which image data for one frame is divided into a predetermined number in accordance with the number of division of the surface light source.

3 is a block diagram showing the backlight control circuit in detail;

Fig. 4 is a view showing clipping error and latitude error generated in local dimming; Fig.

5 is a view showing a macroblock including a corresponding block and neighboring blocks;

Figure 6 shows experimental results comparing the effects of the present invention with the prior art.

7 is a flowchart illustrating a method of driving a liquid crystal display according to an embodiment of the present invention.

Description of the Related Art

10: liquid crystal display panel 11: timing controller

12: data driving circuit 13: gate driving circuit

14: light source control circuit 15: light source driving circuit

16: Backlight unit 141: Histogram analysis unit

142: error calculator 143: luminance calculator

144: upper weight calculation unit 145: dimming control unit

146: PWM generation unit

Claims (14)

A liquid crystal display panel displaying image data; A backlight unit that includes a plurality of light sources and divides the surface light source irradiated to the liquid crystal display panel into blocks of a matrix type; A backlight driving circuit for driving the light sources on a block basis based on a block-by-block PWM signal for controlling lighting; And A weight constant inversely proportional to an average luminance value of image data to be displayed in neighboring blocks which is proportional to a maximum luminance value of image data to be displayed in the block and has an influence on the brightness of the corresponding block, And a backlight control circuit for adjusting the dimming duty of the PWM signal of the corresponding block independently, Wherein the backlight control circuit adjusts the dimming duty of the PWM signal of the corresponding block by comparing the amount of the clapping amount of the corresponding block multiplied by the weighting constant with the amount of the corresponding block, Wherein the amount of the reticle of the corresponding block varies depending on the brightness of the neighboring blocks. delete The method according to claim 1, Wherein the amount of the clapping is obtained by multiplying a clipping error corresponding to the brightness reduction of the light sources due to the local dimming in the corresponding block by a histogram value by the gradation of the image data. The method according to claim 1, Wherein the amount of the leakage is obtained by multiplying a luminance error corresponding to the brightness change of the corresponding block according to the brightness of the neighboring blocks by the histogram value of the image data in the local dimming. The method according to claim 1, The backlight control circuit determines the dimming duty of the PWM signal of the corresponding block by the dimming duty when the amount of clapping of the corresponding block is multiplied by the weighting constant and the amount of the leakage of the corresponding block is equal to each other . The method according to claim 1, The backlight control circuit comprising: A histogram analyzer for analyzing the image data to calculate a histogram value for each gradation; An error calculating unit for calculating a clipping amount and a leakage amount for each block after dimming according to a feedback dimming control signal; A luminance calculation unit for analyzing the image data and calculating an average luminance value and a maximum luminance value for each block; A weighting constant calculating unit for calculating the weighting coefficient for each block; A dimming control unit for comparing a quantity obtained by multiplying the amount of clamping by the weighting constant and a quantity of the leaky amount in each of the blocks to adjust a dimming duty of the dimming control signal for each block; And And a PWM generator for generating the PWM signal according to an optimal dimming duty for each block. The method according to claim 6, Wherein the dimming control unit comprises: Wherein the control unit adjusts the dimming control signal of the corresponding block so that the dimming duty is reduced by a predetermined value if the amount of the leakage is greater than the product of the multiplication amount and then outputs the adjusted dimming control signal to the error calculating unit And the feedback is performed. The method according to claim 6, Wherein the dimming control unit comprises: Wherein the control unit adjusts the dimming control signal of the corresponding block so that the dimming duty is increased by a predetermined value when the amount of the leakage is smaller than the multiplied amount, Wherein the feedback is performed to the sub-pixel. 9. The method according to claim 7 or 8, Wherein the dimming control unit comprises: And determines the dimming duty when the amount of the leakage is equal to the amount multiplied by the feedback block in the corresponding block as the optimum dimming duty. A method of driving a liquid crystal display device having a liquid crystal display panel displaying image data and a backlight unit including a plurality of light sources and dividing a surface light source irradiated on the liquid crystal display panel into blocks of matrix type, (A1) driving the light sources on a block-by-block basis based on a block-by-block PWM signal for controlling lighting; And A weight constant inversely proportional to an average luminance value of image data to be displayed in neighboring blocks which is proportional to a maximum luminance value of image data to be displayed in the block and has an influence on the brightness of the corresponding block, (A2) independently adjusting the dimming duty of the PWM signal of the corresponding block, Wherein the step (A2) adjusts the dimming duty of the PWM signal of the corresponding block by comparing the amount of clapping of the corresponding block multiplied by the weighting constant with the amount of the corresponding block, Wherein the brightness of the corresponding block varies depending on the brightness of the neighboring blocks. delete 11. The method of claim 10, Wherein the amount of the clapping is obtained by multiplying a clipping error corresponding to a decrease in brightness of light sources due to local dimming in the corresponding block by a histogram value by a gradation of the image data. 11. The method of claim 10, Wherein the amount of the leakage is obtained by multiplying a luminance error corresponding to the brightness change of the corresponding block according to the brightness of the neighboring blocks by the histogram value of the image data in the local dimming. Driving method. 11. The method of claim 10, The step (A2) may include: determining a dimming duty of the PWM signal of the corresponding block by the dimming duty when the amount of clapping of the corresponding block is multiplied by the weighting constant and the amount of the corresponding block is equal And a driving method of the liquid crystal display device.

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