KR101419222B1 - Liquid crystal display and driving method thereof - Google Patents

Abstract

The present invention relates to a liquid crystal display device and a driving method thereof, in which a circuit for modulating digital video data is implemented by a circuit without a memory.

The liquid crystal display device includes a representative value extracting unit for extracting a representative value of N (N is a positive integer) -1 frame data; A modulation unit for comparing the source data of the Nth frame with the representative value and selecting the modulation data for selecting the modulation data for improving the response characteristic of the liquid crystal according to the comparison result; And a display driving circuit for converting the modulated data into a data voltage to be displayed on a liquid crystal display panel.

Liquid crystal display, response characteristics, data modulation, frame rate control

Description

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

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and a driving method thereof, in which a circuit for modulating digital video data is implemented by a circuit without memory in order to improve response characteristics of liquid crystal.

A liquid crystal display (LCD) displays an image by adjusting a light transmittance of liquid crystal cells according to a video signal.

Among these liquid crystal display elements, an active matrix type liquid crystal display element in which a switching element is formed for each liquid crystal cell is capable of actively controlling the switching element, which is advantageous for a moving image. A thin film transistor (hereinafter referred to as "TFT") is mainly used as a switching element used in an active matrix type liquid crystal display element.

As can be seen from Equations (1) and (2), the liquid crystal display element has a disadvantage in that the response speed is slow due to inherent characteristics of the liquid crystal such as viscosity and elasticity.

(gamma)는 액정분자의 회전점도(rotational viscosity)를 각각 의미한다. Here,? R denotes a rising time when a voltage is applied to the liquid crystal, Va denotes an applied voltage, VF denotes a freeness transition voltage at which the liquid crystal molecules start tilting, d denotes a liquid crystal The cell gap of the cell is defined as

(gamma) means the rotational viscosity of the liquid crystal molecule, respectively.

Here, τf denotes a falling time at which the liquid crystal is restored to its original value due to the elastic restoring force after the voltage applied to the liquid crystal is turned off, and K denotes the elastic modulus inherent to the liquid crystal.

The liquid crystal response speed of the TN mode (Twisted Nematic mode), which is the liquid crystal mode most commonly used in liquid crystal display devices, can be varied depending on the physical properties of the liquid crystal material, the cell gap, etc. However, 20-30 ms. The response speed of such a liquid crystal is longer than one frame period (NTSC: 16.67 ms). Therefore, as shown in FIG. 1, the voltage charged in the liquid crystal cell proceeds to the next frame before reaching the desired voltage, so that a motion blurring phenomenon occurs in which the screen blurs in the moving image.

Referring to FIG. 1, when the data VD is changed from one level to another level due to a slow response speed, the corresponding display brightness BL does not reach the desired brightness, Can not express. As a result, a motion blurring phenomenon appears in a moving image in a liquid crystal display device, and the image quality deteriorates due to a decrease in a contrast ratio.

을 높게 하게 된다. 따라서, 오버 드라이빙 방식은 액정의 늦은 응답속도를 데이터값의 변조로 보상하여 동영상에서 모션 블러링 현상을 완화시킨다. In order to solve the slow response speed of such a liquid crystal display device, the overdriving method as shown in FIG. 2 modulates the input data VD with preset modulation data MVD and applies the modulated data MVD to the liquid crystal cell The luminance (MBL) is obtained. In this over-driving method, in accordance with whether or not the data is changed so as to obtain a desired luminance corresponding to the luminance value of the input data within one frame period,

. Therefore, the over-driving method compensates for the slow response speed of the liquid crystal by the modulation of the data value, thereby alleviating the motion blurring phenomenon in the moving picture.

The overdriving circuit (Over Driving Circuit) is shown in Fig.

Referring to Fig. 3, the overdriving circuit includes a frame memory 33 for storing data from the data bus 32 and a lookup table 34 for modulating the data.

The frame memory 33 stores the data and supplies the stored data to the lookup table 34 with the previous frame data Fn-1.

The lookup table 34 selects preset modulation data MRGB by using the current frame data Fn and the previous frame data Fn-1 from the frame memory 33 as addresses, as shown in Table 1 below, Lt; / RTI > The lookup table 34 includes a read only memory (ROM) and a memory address control circuit.

division 0 One 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 0 2 3 4 5 6 7 9 10 12 13 14 15 15 15 15 One 0 One 3 4 5 6 7 8 10 12 13 14 15 15 15 15 2 0 0 2 4 5 6 7 8 10 12 13 14 15 15 15 15 3 0 0 One 3 5 6 7 8 10 11 13 14 15 15 15 15 4 0 0 One 3 4 6 7 8 9 11 12 13 14 15 15 15 5 0 0 One 2 3 5 7 8 9 11 12 13 14 15 15 15 6 0 0 One 2 3 4 6 8 9 10 12 13 14 15 15 15 7 0 0 One 2 3 4 5 7 9 10 11 13 14 15 15 15 8 0 0 One 2 3 4 5 6 8 10 11 12 14 15 15 15 9 0 0 One 2 3 4 5 6 7 9 11 12 13 14 15 15 10 0 0 One 2 3 4 5 6 7 8 10 12 13 14 15 15 11 0 0 One 2 3 4 5 6 7 8 9 11 13 14 15 15 12 0 0 One 2 3 4 5 6 7 8 9 10 12 14 15 15 13 0 0 One 2 3 3 4 5 6 7 8 10 11 13 15 15 14 0 0 One 2 3 3 4 5 6 7 8 9 11 12 14 15 15 0 0 0 One 2 3 3 4 5 6 7 8 9 11 13 15

In Table 1, the leftmost column is the data of the previous frame Fn-1, and the best-forward is the data of the current frame Fn.

The overdriving circuit as shown in FIG. 3 requires a frame memory 33 to store previous frame data. This frame memory 33 serves as a main cause of increasing the circuit cost. The applicant of the present application has proposed a method and apparatus for compressing data to be stored in the frame memory 33 and restoring the read data from the frame memory 33 to reduce the memory capacity of the frame memory 33, 98100, 2004-49541, 2004-115730, 2004-116342, 2004-116347, 2006-116974, and the like. However, the circuit cost is still high because there is a limitation in reducing the memory capacity by compressing the data.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a liquid crystal display device and a driving method thereof, in which a circuit for modulating digital video data is implemented by a circuit that does not require a memory in order to improve response characteristics of a liquid crystal.

In order to achieve the above object, a liquid crystal display device according to the present invention includes: a representative value extracting unit for extracting a representative value of N (N is a positive integer) -1 frame data; A modulation unit for comparing the source data of the Nth frame with the representative value and selecting the modulation data for selecting the modulation data for improving the response characteristic of the liquid crystal according to the comparison result; And a display driving circuit for converting the modulated data into a data voltage to be displayed on a liquid crystal display panel.

The liquid crystal display further includes an FRC processing unit connected between the modulating unit and the display driving circuit and using the FRC to temporally disperse the modulated data for a plurality of frame periods.

Wherein the representative value extractor analyzes an average value of RGB pixel values of the one frame image divided by the number of pixels of the liquid crystal display panel and analyzes the RGB pixel values of the one frame image using a histogram to determine a most frequently used mode, Is divided into a luminance component and a chrominance component, and an average value of the luminance component in one frame image and a histogram of a luminance component in the one frame image are analyzed to extract any one of the most frequent modes in the histogram as the representative value.

A driving method of a liquid crystal display according to the present invention includes: extracting a representative value of an Nth (N is a positive integer) -1 frame data; Comparing the source data of the Nth frame with the representative value and selecting the modulation data previously stored in the lookup table to improve the response characteristic of the liquid crystal according to the comparison result; And converting the modulated data into a data voltage to be displayed on a liquid crystal display panel.

The liquid crystal display device and the driving method thereof according to the embodiment of the present invention can remove the memory for storing the previous frame data, thereby simplifying the circuit and reducing the circuit cost.

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

Hereinafter, a preferred embodiment of the present invention will be described with reference to FIGS. 4 and 5. FIG.

4, a liquid crystal display according to an exemplary embodiment of the present invention includes a liquid crystal display panel 45 in which a data line 45 and a gate line 46 intersect and a TFT for driving a liquid crystal cell Clc is formed at an intersection thereof. A data driver 43 for supplying data to the data line 45 of the liquid crystal display panel 47 and a gate for supplying a scan pulse to the gate line 46 of the liquid crystal display panel 47, A modulator 42 for modulating the source data SRGB with preset modulation data MRGB and a modulator 42 for controlling the data driver 43 and the gate driver 44, And a timing controller 41 for supplying the source data SRGB to the memory cell array.

The liquid crystal display panel 47 is formed such that liquid crystal is injected between two glass substrates and data lines 45 and gate lines 46 are mutually orthogonal on the lower glass substrate. The TFT formed at the intersection of the data lines 45 and the gate lines 46 supplies data from the data lines 45 to the liquid crystal cell Clc in response to the scan pulse from the gate line 46 do. To this end, the gate electrode of the TFT is connected to the gate line 46, and the source electrode thereof is connected to the data line 45. The drain electrode of the TFT is connected to the pixel electrode of the liquid crystal cell Clc. A storage capacitor (Cst) for holding the voltage of the liquid crystal cell Clc is formed on the lower glass substrate of the liquid crystal display panel 47. The storage capacitor Cst may be formed between the liquid crystal cell Clc and the front gate line 46 or may be formed between the liquid crystal cell Clc and a separate common line.

The timing controller 41 includes a gate control signal GDC for controlling the operation timing of the gate driving unit 44 using the vertical and horizontal synchronizing signals V and H and the clock CLK, A data control signal DDC for controlling the operation timing, and a control signal for controlling the modulator 42. [ The timing controller 41 samples the digital video data RGB in accordance with the clock CLK and supplies the data RGB as the source data SRGB to the modulator 42 and the modulator 42 And supplies the modulated modulated data (MRGB) to the data driver 43.

The modulation unit 42 compares the representative value of the previous frame with the source data SRGB of the current frame, and selects the modulation data MRGB that satisfies the conditions of Equations 3 to 5 as the comparison result. The modulation data MRGB is stored in a memory of the look-up table, for example, electrically erasable and programmable ROM (EEPROM).

Fn (RGB) <Fn-1 (RGB) ---> Fn (MRGB) <Fn (RGB)

Fn (RGB) = Fn-1 (RGB) ---> Fn (MRGB) = Fn (RGB)

Fn (RGB)> Fn-1 (RGB) ---> Fn (MRGB)> Fn (RGB)

The modulation data MRGB is larger than the current frame Fn when the pixel data value at the same pixel is larger in the current frame Fn than in the previous frame Fn- Whereas it is smaller than the current frame Fn when the current frame Fn is smaller than the previous frame Fn-1. The modulation data MRGB is set to the same value as the current frame Fn if the pixel data value in the same pixel is the same in the previous frame Fn-1 and the current frame Fn. Here, the data of the previous frame Fn-1 is replaced with the representative value of the previous frame as described later.

The modulation section 42 may be embedded in the timing controller 41. [

The data driver 43 stores a shift register, a register for temporarily storing the modulated data (MRGB) from the timing controller 41, and a register for storing the modulated data (MRGB) in response to the clock signal from the shift register, A digital / analog converter for converting the modulation data (MRGB) from the latch to the analog positive / negative polarity gamma compensation voltage, a positive / negative gamma compensation voltage And an output buffer connected between the multiplexer and the data line, and the like. The data driver 43 receives the modulated data MRGB and supplies the modulated data MRGB to the data lines 45 of the liquid crystal display panel 47 under the control of the timing controller 41.

The gate driver 44 is a shift register for sequentially generating scan pulses in response to the gate control signal GDC from the timing controller 41. The gate driver 44 shifts the swing width of the scan pulse to a level suitable for driving the liquid crystal cell Clc A level shifter, and an output buffer. The gate driver 44 supplies a scan pulse to the gate line 46 to turn on the TFTs connected to the gate line 46 to turn on the pixel voltage of the data, The liquid crystal cells Clc of one horizontal line to be selected are selected. The data generated from the data driver 43 is supplied to the liquid crystal cell Clc of one horizontal line selected by being synchronized with the scan pulse.

5 is a circuit diagram showing the data modulator 42 in detail.

5, the modulator 42 according to the present invention includes a representative value extractor 51, a lookup table 52, and a FRC (Frame Rate Control) processor 53.

The representative value extracting unit 51 extracts a representative value Ref from one frame image. The representative value Ref is an average value obtained by dividing the cumulative value of the RGB pixel values of the one frame image by the number of pixels of the liquid crystal display panel 47 and the RGB pixel values of the one frame image by the histogram to obtain the most frequently used RGB pixel mode value , The RGB data is separated into the luminance component (Y) and the chrominance component (UV), and the average value of the luminance component (Y) in one frame image and the histogram of the luminance component (Y) in one frame image are analyzed. Mode. The representative value extracting unit 51 includes a logic circuit that does not include a memory and that calculates an average value using adders and dividers, or a logic circuit that calculates an average value or a mode value in the histogram using a histogram analyzing circuit, an adder, .

The lookup table 52 compares the current frame data RGB (Fn) with the representative value Ref of the previous frame and outputs modulation data previously set under the conditions of Equations 3 to 5, for example, Table 1 Is selected.

On the other hand, the data of the previous frame compared with the current frame data in all gradations is the same as the representative value Ref. Therefore, when data MRGB modulated by the lookup table 52 are displayed as they are, gray scale accumulation may appear in the display image. In order to alleviate the tonality, the FRC processor 53 maps the modulation data (MRGB) modulated by the lookup table (52) to a previously stored dither pattern and stores the dither pattern in a plurality of frame periods And temporally divides the modulated data by time division. Any known dither pattern can be used as the FRC processing method of the FRC processing unit 53. [

As described above, the liquid crystal display device and the driving method thereof according to the embodiment of the present invention generate the modulated data for improving the response characteristic of the liquid crystal by comparing the representative value of the previous frame data with the current frame data, The memory for storing can be removed, and the circuit can be simplified and the circuit cost can be reduced.

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 waveform diagram showing a change in luminance according to data in a conventional liquid crystal display device.

2 is a waveform diagram showing an effect of improving the liquid crystal response characteristic due to overdriving.

3 is a circuit diagram showing an example of an overdriving circuit;

4 is a block diagram showing a liquid crystal display device according to an embodiment of the present invention;

5 is a circuit diagram showing in detail the modulator shown in Fig.

Description of the Related Art

41: timing controller 42: modulation section

43: Data driver 44: Gate driver

45: Data line 46: Gate line

47: liquid crystal display panel 51: representative value extracting unit

52: lookup table 53: FRC processor

Claims (6)

Frame value of the one-frame image is displayed on the liquid crystal display (LCD) so as not to use a memory for storing previous frame data when extracting the representative value, Wherein the RGB value of the 1-frame image is divided into a luminance component and a chrominance component by analyzing the RGB pixel values of the 1-frame image with a histogram to determine the most frequent mode in the histogram and the RGB data of the 1-frame image, A representative value extracting unit for analyzing a mean value and a histogram of components and extracting any one of the most frequent modes in the histogram as the representative value; A lookup table for comparing the data in each pixel of the current frame with the representative value of the previous frame data provided from the representative value extracting unit and selecting the modulated data for improving the response characteristic of the liquid crystal in accordance with the comparison result A modulation section for selecting; And And a display driving circuit for converting the modulated data into a data voltage to be displayed on the liquid crystal display panel. The method according to claim 1, And an FRC processing unit connected between the modulation unit and the display drive circuit, for distributing the modulated data over a plurality of frame periods in a time-wise manner and outputting the modulated data. delete Frame value of the one-frame image is displayed on the liquid crystal display (LCD) so as not to use a memory for storing previous frame data when extracting the representative value, Wherein the RGB value of the 1-frame image is divided into a luminance component and a chrominance component by analyzing the RGB pixel values of the 1-frame image with a histogram to determine the most frequent mode in the histogram and the RGB data of the 1-frame image, Analyzing a mean value and a histogram of the components and extracting any one of the most frequent modes in the histogram as the representative value; Comparing the data in each pixel of the current frame with the single representative value of previous frame data and selecting modulation data in the lookup table to improve the response characteristics of the liquid crystal according to the comparison result; And And converting the modulated data into a data voltage to be displayed on the liquid crystal display panel. 5. The method of claim 4, And the FRC processing unit temporally disperses the modulated data for a plurality of frame periods and outputs the modulated data. delete

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