KR20130071227A - Method of local dimming method and liquid crystal display - Google Patents

Abstract

PURPOSE: A liquid crystal display device and a driving method thereof are provided to simplify a local dimming algorithm, by implementing local dimming on the basis of Black or White (BOW) obtained by comparing data of an input image with center transmittance grayscale. CONSTITUTION: A backlight unit irradiates a light to a display panel (100). A frame rate conversion part (62) performs time division of one frame period into a first frame period and a second frame period by multiplying a frame frequency of an input image. A data modulation part (64) selects a logic value of BOW indicating one of a white grayscale and a black grayscale according to the comparison result obtained by comparing each data of the input image with the pre-established center transmittance grayscale, and modulates the data of the input image on the basis of the BOW, and generates black grayscale or white grayscale data on the basis of the BOW.

Description

Liquid crystal display and its driving method {METHOD OF LOCAL DIMMING METHOD AND LIQUID CRYSTAL DISPLAY}

The present invention relates to a liquid crystal display and a driving method thereof.

BACKGROUND ART [0002] Liquid crystal display devices are becoming increasingly widespread due to features such as light weight, thinness, and low power consumption driving. The transmissive liquid crystal display displays an image by controlling an electric field applied to the liquid crystal layer to modulate the light incident from the backlight unit.

In a liquid crystal display, a motion blur phenomenon may appear in a moving image due to the retention characteristics of the liquid crystal. During the Nth frame period, video data is displayed on the liquid crystal display device, and then the black picture data is supplied to the pixels in the N + 1th frame period to improve the motion picture response time (MPRT). Reduction of BDI (Black Data Insertion) technology is known. The BDI inserts black gray data between video data to be displayed to obtain an impulsive driving effect. As a result, the BDI can reduce motion blur in a video by reducing a video response time (MPRT). Although BDI can reduce the video response time (MPRT), the luminance is lowered due to the black gray data inserted between the video data.

The present invention provides a liquid crystal display and a driving method thereof capable of improving a video response time (MPRT) without deteriorating luminance.

According to an aspect of the present invention, there is provided a liquid crystal display device including: a display panel having a pixel array including data lines, gate lines crossing the data lines, and liquid crystal cells arranged in a matrix; A backlight unit radiating light onto the display panel; A frame rate converter for time-dividing one frame period into a first sub frame period and a second sub frame period by multiplying a frame frequency of an input image; Each of the data of the input image is compared with a preset center transmittance gray scale, and a logic value of a BOW indicating one of a white gray value and a black gray value is selected according to a result of the comparison, and based on the BOW, A data modulator for modulating the data and generating black gray or white gray data based on the BOW; And black gray data or white generated based on the BOW during the second sub frame period after writing data of an input image modulated based on the BOW during the first sub frame period to the pixel array of the display panel. And a display panel driver circuit which writes grayscale data to the pixel array of the display panel.

The center transmittance gradation is set to a data gradation value when the transmittance of the liquid crystal cell is substantially 50%.

The data modulator selects a logic value of the BOW as "0" when the data of the input image is lower than the center transmittance gray level, whereas the data modulator selects a logic value of the BOW when the data of the input image is higher than the center transmittance gray level. 1 ". The BOW is 1 bit data.

The data modulator adds dummy data having each bit "0" to the BOW when the logic value of the BOW is 0, and generates the black gray data, and when the logic value of the BOW is 1, each bit to the BOW. Dummy data with " 1 " is added to generate the black gradation data.

The data modulator modulates data of the input image based on the BOW through the following equation.

는 2~3 사이의 감마 특성 값, X는 상기 BOW를 바탕으로 변조된 입력 영상의 데이터를 각각 의미한다. Here, "# of gray scale" is the number of gray scales that can be expressed, "CTG" is the center transmittance gray, "gray scale" is the gray value of the data of the input image,

Denotes gamma characteristic values between 2 and 3, and X denotes data of an input image modulated based on the BOW.

The data modulator modulates data of an input image based on the BOW using a lookup table in which gray levels and transmittances of data are stored.

When the BOW is "0", the data modulator calculates a compensation transmittance by multiplying the transmittance of the liquid crystal cell corresponding to the gray value of the data of the input image by 2, and inputs the compensation transmittance into the lookup table. The data of the input image is modulated with the data outputted from the input image. When the BOW is "1", the data modulating unit calculates a compensation transmittance by multiplying a result of subtracting a transmittance corresponding to the center transmittance gray scale by a result of subtracting a transmittance corresponding to the gray scale value of the data of the input image. The compensation transmittance is input to the lookup table to modulate the data of the input image with the data output from the lookup table. The transmittance corresponding to the center transmittance gradation is 50%.

The pixel array of the display panel and the light emitting surface of the backlight unit are divided into a plurality of blocks, each of which includes two or more liquid crystal cells. The luminance of the backlight emitting surface of each of the blocks is determined according to the BOW.

The liquid crystal display further includes a local dimming controller for controlling the luminance of the backlight emitting surface for each block based on the BOW.

The local dimming controller determines a dimming value of a block including a liquid crystal cell having a BOW of "1" as a first dimming value, and determines a dimming value of a block including a liquid crystal cell of which the BOW is "0". The second dimming value is lower than the dimming value. The backlight emission surface luminance of the block controlled by the first dimming value is higher than the backlight emission surface luminance of the block controlled by the second dimming value.

The driving method of the liquid crystal display device may include: dividing a frame frequency of an input image by time-dividing one frame period into a first sub frame period and a second sub frame period; Comparing each of the data of the input image with a preset center transmittance gray level and selecting a logic value of a BOW indicating one of a white gray value and a black gray value according to the comparison result; Modulating data of the input image based on the BOW and generating black gray or white gray data based on the BOW; And black gray data or white generated based on the BOW during the second sub frame period after writing data of an input image modulated based on the BOW during the first sub frame period to the pixel array of the display panel. And writing gradation data into a pixel array of the display panel.

The present invention time-divides one frame period into first and second sub frame periods, allocates black gray data or white gray data to modulate the data of the input image according to the data analysis result of the input image in the second sub frame period. . As a result, the present invention can implement a BDI that can improve the video response time (MPRT) without lowering the luminance.

Furthermore, the present invention can simplify the local dimming algorithm by implementing local dimming based on the BOW obtained as a result of comparing the data of the input image and the center transmittance grayscale.

1 is a block diagram showing a data processing apparatus according to a first embodiment of the present invention.
2 is a flowchart showing step by step a control procedure of a data processing method according to a first embodiment of the present invention.
3 is a diagram illustrating an example of multiplying a frame frequency of an input image by 2 times.
4 is a diagram illustrating an example of local dimming blocks.
5 is a diagram illustrating an example of a local dimming block linked to a BOW.
6 is a block diagram showing a data processing apparatus according to a second embodiment of the present invention.
7 is a flowchart showing step by step a control procedure of a data processing method according to a second embodiment of the present invention.
FIG. 8 is a diagram illustrating an example of the lookup table illustrated in FIG. 6.
9 is a block diagram illustrating a liquid crystal display according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Like reference numerals throughout the specification denote substantially identical components. In the following description, when it is determined that a detailed description of known functions or configurations related to the present invention may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

1 is a block diagram showing a data processing apparatus 100 according to a first embodiment of the present invention. 2 is a flowchart showing step by step a control procedure of a data processing method according to a first embodiment of the present invention. The data processing method of FIG. 2 may be implemented by the data processing apparatus 100. 3 is a diagram illustrating an example in which the frame frequency is doubled.

1 to 3, the data processing apparatus 100 may include a frame rate converter 12, a BOW generator 14, a memory controller 16, a memory 18, a data modulator 20, and data. A transmission unit 22 and the like.

The frame rate converter 12 receives digital video data RGB of an input image and timing signals such as a data enable signal DE and a main clock CLK synchronized with the data RGB. The frame rate converter 12 multiplies the frame frequency of the input video by double the frame frequency FR (N) for the first sub frame period SFa (N) and the second sub frame period SFb (N). (S1 and S2 in FIG. 2) Each of the first sub frame period SFa (N) and the second sub frame period SFb (N) is a half frame period. The frame rate converter 12 transmits a subframe identification signal for distinguishing the first and second subframe periods SFa (N) and SFb (N) to the data modulator 20 and the data transmitter 22. do.

The frame frequency of the input image is 50 Hz in PAL (Phase Alternate Line) and 60 Hz in National Television Standards Committee (NTSC). Therefore, in the PAL method, the input frequency of the frame rate converter 12 is 50 Hz, and the output frame frequency doubled is 100 Hz. In the NTSC method, the input frame frequency of the frame rate converter 112 is 60 Hz, and the output frame frequency doubled is 120 Hz.

The BOW generation unit 14 compares the data of the input image with a preset center transmittance gray scale (CTG), and selects a logical value of black or white gray scale data (hereinafter referred to as "BOW") according to the comparison result. (S3 to S5 of FIG. 2) The BOW data generation unit 14 selects '0' as BOW (BOW = 0) when the data gray level of the input image is lower than the center transmittance gray scale (CTG), whereas the BOW data generation unit 14 When the data gray level is equal to or higher than the center transmittance gray level (CTG), '1' is selected as BOW (BOW = 1). It should be noted that the BOW is not selected from the input image, but generated by comparison with the center transmittance gray scale (CTG) in the BOW generation unit 14. Since the BOW is 1 or 0, 1 bit is allocated for each data of the input image and stored in the memory 18.

The first subframe data Dataa is 8 bit data of the input image, whereas the second subframe data Datab is selected as a BOW of 1 bit. Therefore, the size and memory capacity of the second subframe data Datab are much smaller than the first subframe data Dataa.

Assuming that the transmittance of the liquid crystal cell (or subpixel) is 100% when data of the highest gray value is written in the pixel array of the display panel, the center transmittance gray scale (CTG) has a transmittance of 50% of the liquid crystal cell, or It is set to the data gray scale value written in the liquid crystal cell when the transmittance closest to is. When the pixel data of the input image is 8 bit data, 256 gray levels can be expressed. In this case, the gray level closest to the center transmittance gray level (CTG) in the 2.2 gamma characteristic curve is '187'. The center transmittance gray scale (CTG) is not limited to '187' because it depends on the number of pixel data bits of the input image and the slope of the gamma characteristic curve.

The memory control unit 16 stores the BOW as the second sub frame data Datab in the memory 18, and supplies the first sub frame data Dataa to the data modulator 20 (S6 in FIG. 2). In addition, the memory controller 16 generates a write enable signal and a read enable signal to control data input / output of the memory 18.

In the first sub frame period SFa (N) where the frame frequency of the input image is doubled and is set to the half frame period, the data of the input image is displayed on the liquid crystal cell and the second sub frame is the remaining half frame period. When black gray or white gray is displayed on the liquid crystal cell in the period SFb (N), the luminance of the image reproduced on the display panel is different from the luminance of the input image. When the raw data of the input image is maintained in the liquid crystal cell for one frame period, in order to obtain a transmittance equal to the transmittance of the liquid crystal cell, the gray level of the first subframe data Dataa is larger than the raw data of the input image when BOW = 0. On the other hand, when BOW = 1, the gray level of the first subframe data Dataa should be modulated to a lower gray level value than the original data of the input image. To this end, the data modulator 20 modulates the data of the input image in the same manner as in Equation 1 to generate the first subframe data Dataa (S7 of FIG. 2).

The data modulator 20 may include a BOW generator 14, a memory controller 16, a memory 18, and a data transmitter 22.

The data modulator 20 supplies the first subframe data Dataa modulated based on Equation 1 to the data transmitter 22 during the first subframe period SFa (N).

는 감마 특성을 의미한다.

는 2~3 사이의 값으로 설정될 수 있다. X는 제1 서브 프레임 기간(SFa(N))에 액정셀에 기입될 데이터의 계조이다.Here, "# of gray scale" is a number of gray scales that can be expressed, for example, # of gray scale is 2 ⁸ = 256 in ^8- bit data and # of gray scale is 2 ⁶ = 64 in ^6- bit data. "gray scale" is a data gray level of the input image. When 8 bit data is input and the gray value of the data is 170, "# of gray scale " is 256 and " gray scale "

Means gamma characteristic.

May be set to a value between 2 and 3. X is the gradation of data to be written in the liquid crystal cell in the first sub frame period SFa (N).

= 2.2인 감마 커브에서 액정셀(또는 서브 픽셀)의 투과율(T)이 T = 50%와 가장 가까운 계조인 CTG = 187 이다. 입력 영상 데이터의 계조가 "128"이면, 그 데이터의 계조는 CTG = 187 보다 작으므로 BOW = 0이 된다. 이 경우에, 데이터 변조부(20)는 수학식 1에 의해 입력 영상 데이터 "128"을 "175"로 상향 변조하여 제1 서브 프레임 데이터(Datab)로서 출력한다.Taking the data modulation method as an example,

The transmittance T of the liquid crystal cell (or subpixel) in the gamma curve of = 2.2 is CTG = 187, which is the gray level closest to T = 50%. If the gradation of the input video data is "128", the gradation of the data is smaller than CTG = 187 so that BOW = 0. In this case, the data modulator 20 up-modulates the input image data "128" to "175" by using Equation 1 and outputs it as the first subframe data Datab.

= 2.2인 감마 특성 커브에서 액정셀의 투과율은 21.76%이다. 1/2 프레임 기간으로 설정된 제2 서브 프레임 기간 동안 그 액정셀의 투과율은 BOW = 0 이므로 블랙 계조인 0으로 낮아진다. 따라서, 1/2 프레임 기간으로 설정된 제1 서브 프레임 기간에 그 액정셀의 투과율은 21.76%의 두배(×2)가 되어야 한다. 그 결과, 시간적으로 적분하면 21.76%가 되어야 하므로 그 액정셀의 투과율이 대략 43.3%로 되는 계조는 전술한 데이터 변조 결과와 마찬가지로,

= 2.2인 감마 특성 커브에서 "175" 이다. Explained by the transmittance of the liquid crystal cell, when the gradation of data is "128"

The transmittance of the liquid crystal cell in the gamma characteristic curve of = 2.2 is 21.76%. The transmittance of the liquid crystal cell during the second sub frame period set to the 1/2 frame period is lowered to zero, which is black gradation because BOW = 0. Therefore, the transmittance of the liquid crystal cell in the first sub frame period set to 1/2 frame period should be twice (× 2) of 21.76%. As a result, since the time integration should be 21.76%, the gradation in which the transmittance of the liquid crystal cell becomes approximately 43.3% is similar to the above-described data modulation result.

"175" in the gamma characteristic curve = 2.2.

As another example, when the gray level of the input image data is "210", the gray level of the data is larger than CTG = 187, resulting in BOW = 1. In this case, the data modulator 20 down-modulates the input image data “210” to “146” based on Equation 1 and outputs the first sub frame data Dataa.

The data transmitter 22 selects the output Dataa of the data modulator 20 during the first sub frame period SFa (N) and transmits the data to the data driver not shown, and the second sub frame period SFb ( N)), dummy data is added to the BOW, which is an output Data of the memory 18, and transmitted to the data driver. (S8 to S10 of FIG. 2) The data transmitter 22 inputs 8 bit data to the data driver. When BOW = 0, 7-bit dummy data "0000000 ₂ " is added to BOW = 0, and 8-bit black gray data "00000000 ₂ " is output in the second sub frame period SFb (N), and BOW If = 1, 7-bit dummy data "1111111 ₂ " is added to BOW = 1, and 8-bit white tone data "11111111 ₂ " is output in the second sub frame period SFb (N). The data driver generates the positive / negative data voltage by modulating the digital video data RGB ′ input from the data transmitter 22 into the positive / negative gamma compensation voltage. The data voltage output from the data driver is charged in the liquid crystal cells formed in the pixel arrays of the display panel through the data lines of the display panel. As a result, the display panel displays the data Data modulated by the data modulator during the first sub frame period SFa (N), and the black or white gray level during the second sub frame period SFb (N). (S11 in FIG. 2)

In order to improve contrast of an image displayed on a liquid crystal display, a backlight dimming control method of adjusting a brightness of a backlight according to an input image is applied. The backlight dimming control method may reduce power consumption by adaptively adjusting the brightness of the backlight according to the input image.

The backlight dimming method includes a global dimming method for adjusting the luminance of the entire display surface and a local dimming method for dividing the display screen into a plurality of blocks and locally adjusting the luminance of the display surface. have.

The global dimming method may improve dynamic contrast measured between the previous frame and the next frame. The local dimming method locally improves the brightness of the display surface within one frame period, thereby improving static contrast, which is difficult to improve with the global dimming method.

The local dimming method divides the backlight emitting surface into a plurality of blocks to increase the backlight luminance of a block in which the image is bright, while lowering the backlight luminance of a block in which the image is relatively dark. The local dimming method includes analyzing an input image, calculating a representative value for each block according to an analysis result of the input image, calculating a dimming value for each block based on the representative value for each block, and a spatial filter. And it is implemented as a complex algorithm including several steps, such as the step of distributing the dimming value for each block by using a temporal filter. In contrast, the local dimming algorithm can be simplified by applying the aforementioned data processing method to the local dimming algorithm.

4 is a diagram illustrating an example of local dimming blocks. 5 is a diagram illustrating an example of a local dimming block linked to a BOW.

4 and 5, the liquid crystal display of the present invention virtually divides the pixel arrays of the display panel and the light emitting surface of the backlight into a plurality of blocks B11 to B45 in order to implement local dimming. Each of the blocks B11 to B45 includes two or more pixels. The pixels include a red subpixel, a green subpixel, and a blue subpixel for color implementation, and each of the subpixels includes a liquid crystal cell. The light sources irradiating light to the blocks B11 to B45 independently control the luminance of each of the blocks according to the local dimming value. For example, light sources controlled by a high dimming value are turned on at a high duty ratio in pulse width modulation (PWM) to increase backlight brightness. On the other hand, light sources controlled by a low dimming value are turned on at a low duty ratio in pulse width modulation (PWM) to lower the backlight brightness. The maximum duty ratio may be 100% and the minimum duty ratio may be 0%.

As a result of comparing the digital video data RGB of the input image with the center transmittance gray scale (CTG), the light emitting surface of the backlight irradiating light to the blocks B22, B23, B32, and B34 containing liquid crystals having BOW = 1 is During the second sub frame period SFb (N), light may be turned on at a high luminance due to light sources that light at the first dimming value. The first dimming value may be a maximum dimming value. The blocks B22, B23, B32, and B34 including the liquid crystal cells having BOW = 1 may be a block in which the BOW of all subpixel data included in the block is BOW = 1, or the number of data having BOW = 1 is included in the block. There may be many blocks with a predetermined ratio or more with respect to all the sub pixel data. Here, the predetermined ratio may be a ratio selected between 51% and 100%.

The light emitting surface of the backlight irradiating light to the blocks B11 to B15, B21, B24 to B25, B31, B34 to B35, and B41 to B45 including the liquid crystal cells having BOW = 0 is defined as the second sub frame period SFb ( N)) may be turned on at low luminance due to the light sources controlled to the second dimming value lower than the first dimming value. The second dimming value may be a minimum dimming value. Blocks B11 to B15, B21, B24 to B25, B31, B34 to B35, and B41 to B45 including liquid crystal cells having BOW = 0 are blocks in which BOW = 0 of all sub-pixel data included in the block is BOW = 0. For example, the number of data having BOW = 0 may be more blocks than a predetermined ratio with respect to all subpixel data included in the block. The predetermined ratio may be a ratio selected between 51% and 100%.

This local dimming method can be equally applied to the first sub frame period SFa (N). Meanwhile, the backlight emission surface irradiating light to all the blocks B11 to B45 during the first sub frame period SFa (N) may be turned on at the same brightness by light sources that emit the same dimming value.

6 is a block diagram showing a data processing apparatus according to a second embodiment of the present invention. 7 is a flowchart showing step by step a control procedure of a data processing method according to a second embodiment of the present invention. The data processing method of FIG. 7 may be implemented by the data processing apparatus 100 illustrated in FIG. 6. FIG. 8 is a diagram illustrating an example of a look-up table 66 illustrated in FIG. 6.

6 to 8, the data processing apparatus 100 may include a frame rate converter 62, a data modulator 64, a lookup table 66, a data transmitter 68, and the like.

The frame rate converter 62 receives digital video data RGB of an input image and timing signals such as a data enable signal DE and a main clock CLK synchronized with the data RGB. The frame rate converter 62 multiplies the frame frequency of the input video by double the frame frequency FR (N) for the first sub frame period SFa (N) and the second sub frame period SFb (N). (S11 and S12 in FIG. 7) Each of the first sub frame period SFa (N) and the second sub frame period SFb (N) is a half frame period. The frame rate converter 62 transmits a subframe identification signal for distinguishing the first and second subframe periods SFa (N) and SFb (N) to the data modulator 64.

In the lookup table 66, the transmittance of the liquid crystal cell obtained for each gray level of the data through the experiment of the transmittance of the liquid crystal cell for each gray level of the data is stored together with the gray level of the data. When the data is input, the lookup table 66 outputs a transmittance T of the data. When the transmittance T is input, the lookup table 66 outputs a gray level of data corresponding to the transmittance T. FIG.

The data modulator 64 compares the data of the input image with the center transmittance gray scale (CTG), and selects a BOW according to the comparison result. (S12 to S14 in FIG. 7) When the data gray level is lower than the center transmittance gray scale (CTG), the BOW is selected as BOW = 0, while when the data gray level of the input image is higher than the center transmittance gray scale (CTG), the BOW is selected as BOW = 1.

The data modulator 64 may check the transmittance of the liquid crystal cell with respect to the data gray level of the input image by inputting data of the input image to the lookup table 66 and receiving data of transmittance output from the lookup table 66. The data modulator 64 inputs a compensation transmittance calculated based on the transmittances of the BOW and the input image data to the lookup table 66 and modulates the data of the input image with the data gradation received from the lookup table.

When BOW = 0, the data modulator 64 multiplies the transmittance T1 of the liquid crystal cell corresponding to the data gray scale of the input image by 2 to calculate the compensated transmittance T as T = T1 * 2, and the compensated transmittance T ) Is input to the lookup table 66 to modulate the data of the input image with the data output from the lookup table 66. When the BOW = 1, the data modulator 64 multiplies the result of subtracting the transmittance T2 of the liquid crystal cell corresponding to the data gray scale of the input image by the transmittance T2 corresponding to the center transmittance gray scale (CTG) and multiplying by 2 to compensate the transmittance. (T) is calculated as T = (T1-T2) * 2, and the compensation transmittance T is input to the lookup table 66 to modulate the data of the input image with the data output from the lookup table 66. (S15 to S16 of FIG. 7) The transmittance T2 corresponding to the center transmittance gray scale CTG may be 50% as described above.

The lookup table 66 responds to the transmittance T input from the data modulator 64 and outputs the gray level of the data corresponding to the transmittance T as the first subframe data Datab. For example, the lookup table 66 outputs a data gray value “128” as the first subframe data Datab when the transmittance T input from the data modulator 64 in FIG. 8 is 21.77.

The data modulation unit 64 supplies the data transmission unit 68 with data modulated using the BOW and lookup table 66. The data modulated by the data modulator 64 satisfies Equation (1).

The data transmitter 68 selects the modulated data input from the data modulator 64 during the first sub frame period SFa (N) and transmits the modulated data to a data driver (not shown), and the second sub frame period SFb ( N)) adds dummy data to the BOW input from the data modulator 64 and transmits the dummy data to the data driver. When 8-bit data is input to the data driver, the data transfer unit 68 adds 7-bit dummy data "0000000 ₂ " with each bit "0" to BOW = 0 when BOW = 0, and black-bit data of 8 bits. "00000000 ₂ " is output in the second sub frame period SFb (N). When BOW = 1, the data transfer unit 68 adds 7-bit dummy data "1111111 ₂ " having each bit "1" to BOW = 1, and adds 8-bit white gray scale data "11111111 ₂ " to the second sub frame period ( Output to SFb (N)). The data driver modulates the digital video data RGB ′ input from the data transmitter 68 to the positive / negative gamma compensation voltage to generate the positive / negative data voltage. The data voltage output from the data driver is charged in the liquid crystal cells formed in the pixel arrays of the display panel through the data lines of the display panel. As a result, the display panel displays data modulated by the data modulator 64 during the first sub frame period SFa (N), and black or white gray level during the second sub frame period SFb (N). Is displayed.

The data processing apparatus and method according to the second embodiment of the present invention can simplify the local dimming algorithm as shown in FIGS. 4 and 5 by linking the BOW to the local dimming method in the same manner as the first embodiment described above.

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

Referring to FIG. 9, the liquid crystal display of the present invention includes a display panel 300, a display panel driver, a timing controller 110, a data processor 100, a backlight unit 200, a light source driver 210, and local dimming. Control unit 120 and the like.

The display panel 300 includes two glass substrates, and a liquid crystal layer is formed therebetween. In the display panel 300, liquid crystal cells are arranged in a matrix by a cross structure between the data lines 301 and the gate lines 302. A pixel electrode of a liquid crystal cell connected to data lines 301, gate lines 302, TFTs, and TFTs may be formed on a thin film transistor (“TFT”) array substrate of the display panel 300. , And a storage capacitor and the like are formed. The black matrix, the color filter, and the common electrode are formed on the color filter substrate of the display panel 300.

The liquid crystal display of the present invention is implemented in a vertical electric field driving method such as twisted nematic (TN) mode and a vertical alignment (VA) mode, or a horizontal electric field driving method such as IPS (In Plane Switching) mode and FFS (Fringe Field Switching) mode. Can be.

For local dimming, the pixel array of the display panel 300 and the light emitting surface of the backlight unit 200 opposite thereto are virtually divided into a plurality of blocks as described above.

The timing controller 110 receives timing signals Vsync, Hsync, DE, and CLK from an external host system, and supplies digital video data RGB to the data driver 122. The timing signals Vsync, Hsync, DE, and CLK include a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync, a data enable signal DE, a main clock CLK, and the like. The vertical synchronization signal Vsync and the horizontal synchronization signal Hsync may be omitted.

The timing controller 110 may include timing control signals DDC, for controlling an operation timing of the data driver 122 and the gate driver 124 based on the timing signals Vsync, Hsync, DE, and CLK from the host system. GDC). The timing controller 110 supplies digital video data RGB of an input image input from the host system to the data processing apparatus 100, and outputs the digital video data RGB ′ output from the data processing apparatus 100. Supply to the driving unit 122. In addition, the timing controller 110 supplies the BOW output from the data processing apparatus 100 to the local dimming control unit 120.

The host system may be any one of a TV system, a home theater system, a personal computer (PC), a broadcast set-top box, a navigation system, a DVD player, a Blu-ray player, and a phone system. The host system transmits the timing signals Vsync, Hsync, DE, and CLK synchronized with the data RGB to the timing controller 110 together with the digital video data RGB.

The data processing apparatus 100 is implemented in the first embodiment or the second embodiment described above. The data processing apparatus 100 modulates the data of the input image based on Equation 1 or by using a lookup table 66 in which data and transmittances satisfying Equation 1 are set, and thus, the first sub frame period SFa (N). ), Digital video data RGB 'to be written to the pixel array is output. The data processing apparatus 100 generates and outputs a BOW by comparing the data of the input image with the center transmittance gray scale (CTG), and adds and outputs dummy data to the BOW.

The display panel driver writes the digital video data RGB ′ input from the timing controller 110 to the pixel array of the display panel 300 using the data driver 122 and the gate driver 124. The digital video data RGB 'includes data modulated by the above-described data modulators 20 and 64 and black or white gray data in which dummy data is added to the BOW.

The data driver 122 latches the digital video data RGB ′ under the control of the timing controller 110. The data driver 122 converts the digital video data RGB 'into a positive / negative analog data voltage using the positive / negative gamma compensation voltage and supplies the converted data to the data lines 301. The gate driver 124 sequentially supplies gate pulses synchronized with the data voltage output from the data driver 122 to the gate lines 302.

The backlight unit 200 is disposed under the display panel 300. The backlight unit 200 uniformly irradiates light to the display panel 300 including a plurality of light sources individually controlled for each block by the light source driver 210. The backlight unit 200 may be implemented as a direct type backlight unit or an edge type backlight unit. The light source of the backlight unit may be implemented as a point light source such as a light emitting diode (LED).

The light source driver 210 adjusts the lighting time of the light sources according to the duty ratio of PWM determined according to the dimming value for each block input from the local dimming controller 120. The duty ratio of the light sources is individually controlled for each block according to the dimming value for each block. As described above, the local dimming controller 120 determines the dimming value for each block based on the BOW input from the timing controller 110 to control the light source driver 210.

The data processing apparatus 100 and the local dimming controller 120 may be built in the timing controller 110.

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.

12, 62: frame rate converter 14: BOW generator
16: memory controller 18: memory
20, 64: data modulation section 22, 68: data transmission section
66: lookup table 100: data processing device
110: timing controller 120: local dimming control unit
122: data driver 124: gate driver
200: backlight unit 210: light source driver
300: display panel

Claims (17)

A display panel having a pixel array including data lines, gate lines crossing the data lines, and liquid crystal cells arranged in a matrix;
A backlight unit radiating light onto the display panel;
A frame rate converter for time-dividing one frame period into a first sub frame period and a second sub frame period by multiplying a frame frequency of an input image;
Each of the data of the input image is compared with a preset center transmittance gray scale, and a logic value of a BOW indicating one of a white gray value and a black gray value is selected according to a result of the comparison, and based on the BOW, A data modulator for modulating the data and generating black gray or white gray data based on the BOW; And
After writing the data of the input image modulated based on the BOW in the first sub frame period to the pixel array of the display panel, the black gray data or white gray level generated based on the BOW during the second sub frame period A display panel driver circuit for writing data to the pixel array of the display panel;
And the center transmittance gradation is set to a data gradation value when the transmittance of the liquid crystal cell is substantially 50%. The method of claim 1,
Wherein the data modulator comprises:
When the data of the input image is lower than the center transmittance gradation, the logic value of the BOW is selected as "0",
When the data of the input image is equal to or greater than the center transmittance gradation, the logic value of the BOW is set to "1",
And the BOW is 1 bit data. 3. The method of claim 2,
Wherein the data modulator comprises:
When the logic value of the BOW is 0, dummy data having each bit "0" is added to the BOW to generate the black gray data.
And when the logic value of the BOW is 1, the black gradation data is generated by adding dummy data having each bit "1" to the BOW. The method of claim 1,
The data modulator modulates data of the input image based on the BOW through the following equation,

Here, "# of gray scale" is the number of gray scales that can be expressed, "CTG" is the center transmittance gray, "gray scale" is the gray value of the data of the input image,

Is a gamma characteristic value between 2 and 3, and X is data of the input image modulated based on the BOW. 3. The method of claim 2,
The data modulator
And a look-up table in which gray levels and transmittances of data are stored to modulate data of an input image based on the BOW. The method of claim 5, wherein
Wherein the data modulator comprises:
If the BOW is "0", the transmittance of the liquid crystal cell corresponding to the gray value of the data of the input image is multiplied by 2 to calculate a compensation transmittance, and the compensation transmittance is input to the lookup table to output data from the lookup table. Modulate the data of the input image with
When the BOW is "1", the transmittance of the liquid crystal cell corresponding to the gray value of the data of the input image is multiplied by the result of subtracting the transmittance corresponding to the center transmittance gray level to calculate a compensation transmittance. Modulating the data of the input image with data inputted to the lookup table and outputted from the lookup table,
The transmittance corresponding to the center transmittance gradation is 50%. 3. The method of claim 2,
The pixel array of the display panel and the light emitting surface of the backlight unit are divided into a plurality of blocks.
Each of the blocks includes two or more liquid crystal cells
And a backlight emission surface luminance of each of the blocks is determined according to the BOW. The method of claim 7, wherein
And a local dimming controller for controlling the luminance of the backlight emitting surface for each block based on the BOW. The method of claim 8,
The local dimming control unit,
The dimming value of the block including the liquid crystal cell of which the BOW is "1" is determined as a first dimming value,
The dimming value of the block including the liquid crystal cell having the BOW of "0" is determined as a second dimming value lower than the first dimming value,
And the backlight light emitting surface luminance of the block controlled by the first dimming value is higher than the backlight light emitting surface luminance of the block controlled by the second dimming value. A liquid crystal display including a display panel having a pixel array including data lines, gate lines intersecting the data lines, and liquid crystal cells arranged in a matrix, and a backlight unit radiating light to the display panel. In the driving method of,
Multiplying the frame frequency of the input image by time division of one frame period into a first sub frame period and a second sub frame period;
Comparing each of the data of the input image with a preset center transmittance gray level and selecting a logic value of a BOW indicating one of a white gray value and a black gray value according to the comparison result;
Modulating data of the input image based on the BOW and generating black gray or white gray data based on the BOW; And
After writing the data of the input image modulated based on the BOW in the first sub frame period to the pixel array of the display panel, the black gray data or white gray level generated based on the BOW during the second sub frame period Writing data to a pixel array of the display panel;
And the center transmittance gradation is set to a data gradation value when the transmittance of the liquid crystal cell is substantially 50%. 11. The method of claim 10,
When the data of the input image is lower than the center transmittance gradation, the logic value of the BOW is selected as "0",
When the data of the input image is greater than or equal to the center transmittance gradation, the logic value of the BOW is selected as "1".
And the BOW is 1 bit data. The method of claim 11,
Modulating the data of the input image based on the BOW and generating black gray or white gray data based on the BOW,
Generating black data by adding dummy data having each bit " 0 " to the BOW when the logic value of the BOW is 0; And
And generating the black gradation data by adding dummy data having each bit "1" to the BOW when the logic value of the BOW is 1. 11. The method of claim 10,
Modulating the data of the input image based on the BOW and generating black gray or white gray data based on the BOW,
Modulate the data of the input image based on the BOW through the following formula,

Here, "# of gray scale" is the number of gray scales that can be expressed, "CTG" is the center transmittance gray, "gray scale" is the gray value of the data of the input image,

Is a gamma characteristic value between 2 and 3, and X represents data of an input image modulated based on the BOW. The method of claim 11,
Modulating the data of the input image based on the BOW and generating black gray or white gray data based on the BOW,
A method of driving a liquid crystal display device, characterized in that the data of the input image is modulated on the basis of the BOW by using a lookup table in which data gray scales and transmittances are stored. 15. The method of claim 14,
Modulating the data of the input image based on the BOW and generating black gray or white gray data based on the BOW,
If the BOW is "0", the transmittance of the liquid crystal cell corresponding to the gray value of the data of the input image is multiplied by 2 to calculate a compensation transmittance, and the compensation transmittance is input to the lookup table to output data from the lookup table. Modulating the data of the input image with; And
When the BOW is "1", the transmittance of the liquid crystal cell corresponding to the gray value of the data of the input image is multiplied by the result of subtracting the transmittance corresponding to the center transmittance gray level to calculate a compensation transmittance. Modulating data of the input image with data input to the lookup table and output from the lookup table;
And a transmittance corresponding to the center transmittance gradation is 50%. The method of claim 11,
The pixel array of the display panel and the light emitting surface of the backlight unit are divided into a plurality of blocks.
Each of the blocks includes two or more liquid crystal cells
And a backlight emission surface luminance of each of the blocks is determined according to the BOW. 17. The method of claim 16,
Controlling the brightness of a backlight emitting surface for each block based on the BOW;
Controlling the brightness of the backlight emitting surface for each block based on the BOW,
Determining a dimming value of a block including a liquid crystal cell having the BOW of "1" as a first dimming value; And
Determining a dimming value of a block including a liquid crystal cell having a BOW of "0" as a second dimming value lower than the first dimming value,
And the backlight light emitting surface luminance of the block controlled by the first dimming value is higher than the backlight light emitting surface luminance of the block controlled by the second dimming value.

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