KR101992887B1 - Luquid crystal display device and method for diriving thereof - Google Patents

Abstract

The present invention discloses a liquid crystal display device. More particularly, the present invention relates to a liquid crystal display device and a driving method thereof, which improve image quality deterioration such as afterimages when a full-white specific pattern is implemented.
According to an exemplary embodiment of the present invention, a liquid crystal display device includes a liquid crystal panel, a data driver providing a data voltage thereto, and an image signal input from an external system to analyze the image signal having a predetermined pattern, thereby changing the gradation range. It comprises a timing controller including an image compensation unit provided to one data driver, characterized in that it comprises a setting information storage unit for storing a setting value which is a reference for changing the gradation range.
According to this structure, the liquid crystal display of the present invention, when the image of the full-black and full-white alternately, such as the mosaic pattern is received by analyzing the pattern of the video signal provided from the external system, the predetermined value Accordingly, the gradation range of the image signal is varied to minimize the application of the DC voltage corresponding to the maximum gradation value to the liquid crystal cell, thereby improving the afterimage problem.

Description

Liquid crystal display and its driving method {LUQUID CRYSTAL DISPLAY DEVICE AND METHOD FOR DIRIVING THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display, and more particularly, to a liquid crystal display and a method of driving the same, which improve image quality deterioration such as an afterimage when a full-white specific pattern is implemented.

A liquid crystal display device displays an image on a screen by controlling an amount of light transmission by forming an electric field between two electrodes, called a common electrode and a pixel electrode, and controlling the rotation angle of the liquid crystal to display a desired image on a screen. Is input to match the reference gamma voltage to generate a data voltage, and the data voltage is applied to the pixel electrode to form an electric field between the common electrodes to which the common voltage is applied.

1A is a diagram of a waveform of a conventional reference gamma voltage, and FIG. 1B is a diagram of a voltage configuration of a reference gamma voltage. As shown in FIG. 1A, reference gamma voltages GMA1 to GMA5 of positive potentials and reference gamma voltages GMA6 to GMA10 of negative potentials are defined around the common voltage Vcom, and the voltage levels thereof are set in advance. .

Also, in order to compensate for the offset voltage due to the panel characteristics, the reference gamma voltage is such that the voltage level of the actual common voltage Vcom is completely symmetrical between the bipolar gamma value and the negative gamma value, as shown in FIG. 1B. It is determined not to the voltage level but to a lower voltage level (b).

That is, the minimum value and the maximum value of the gray level for the image are previously determined according to the reference gamma voltages GMA1 and GMA10. Accordingly, the maximum voltage level applied to the pixel electrode is also predetermined.

2 is a diagram schematically illustrating a pixel structure of a liquid crystal panel included in a general liquid crystal display device, in which a plurality of data lines DL1 to DLn and a plurality of gate lines GL1 to GLm cross each other. A thin film transistor TFT and a liquid crystal cell LC are formed in each pixel area to display a screen.

In the case of the normally black liquid crystal panel on one screen, the above-described liquid crystal display device can determine the correct image display performance. As shown in FIG. The afterimage test of the liquid crystal display is performed by displaying a mosaic pattern in which a full-white gray level is alternately implemented for a long time.

Subsequently, the image is converted to a halftone pattern to determine whether the afterimage of the previous mosaic pattern remains, thereby determining the afterimage characteristic of the liquid crystal panel. The afterimage characteristic is generated by the accumulation of electric charges applied to the liquid crystal cell LC. The DC voltage in the liquid crystal layer is generated, and the ionic impurities contained in the liquid crystal layer move to polarize the alignment layer, thereby generating residual DC voltage. It is known that the pretilt of the liquid crystal changes and the orientation regulating force changes. In particular, the greater the difference between the grayscale values corresponding to the full-black and the full-white, the larger the image intensity is caused. This shortens the lifespan of the liquid crystal display device and causes a decrease in image quality.

In order to overcome this problem, when setting the reference gamma voltage for the image having a normal pattern and the image having a mosaic pattern separately, a reference gamma voltage generation unit for this should be further provided, thus increasing the manufacturing cost, There is a limit that the configuration circuit of the liquid crystal display device is increased.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and an object of the present invention is to improve an afterimage problem occurring in a liquid crystal panel by an image in which full-black and full-white are alternately implemented like a mosaic pattern. The present invention provides a device and a driving method thereof.

In order to achieve the above object, a liquid crystal display device according to a preferred embodiment of the present invention, a liquid crystal panel; A data driver providing a data voltage to the liquid crystal panel; A timing controller including an image compensator for analyzing a video signal input from an external system and changing the gray scale range to provide the data driver when the video signal has a predetermined pattern; And a setting information storage unit which stores a setting value which is a reference for changing the gradation range.

The predetermined pattern may be a mosaic pattern in which the full-black and full-white areas are alternately repeated in one screen.

The image compensator may include: a gradation section discriminating unit configured to calculate a frequency of the gradation value for each frame of the image signal, and determine whether the calculated gradation value belongs only to 0 gradation and 255 gradation; A setting value extracting unit for requesting the setting information storage unit to extract the setting value if it is determined that the video signal has a mosaic pattern; And a gradation range changer for changing a gradation range of the video signal in response to the extracted set value.

The gray scale ranges from a gray value corresponding to full-black to at least a gray value lower than full-white.

The gradation range is characterized by changing the gradation value between 246 to 255 gradations to 245 gradation values.

The setting information storage unit is an EEPROM storing the setting values in the form of an LUT.

In order to achieve the above object, a driving method of a liquid crystal display device according to an embodiment of the present invention, receiving a timing signal and image data from an external system; Analyzing the video signal and changing a gradation range when the video signal has a predetermined pattern; And aligning and converting an original video signal or a video signal having a gray scale range changed.

The predetermined pattern may be a mosaic pattern in which the full-black and full-white areas are alternately repeated in one screen.

The step of changing the gradation range when the image signal has a constant pattern by analyzing the video signal, calculates the frequency of the gradation value for each frame of the video signal, and the calculated gradation value belongs only to 0 gradation and 255 gradations. Determining whether or not; If it is determined that the video signal has a mosaic pattern, requesting the setting information storage unit to extract the setting value; And changing the gradation range of the video signal in response to the extracted set value.

The gray scale ranges from a gray value corresponding to full-black to at least a gray value lower than full-white.

The changing of the gradation range of the video signal in response to the extracted setting value may include changing a gradation value between 246 to 255 gradations of the video signal to 245 gradation values.

According to an exemplary embodiment of the present invention, when the image of the full-black and full-white alternately is received, such as a mosaic pattern, by analyzing the pattern of the image signal provided from the external system, the gray level of the image signal according to a preset setting value By varying the range and minimizing the application of the DC voltage corresponding to the maximum gradation value to the liquid crystal cell, the afterimage problem of the liquid crystal display device can be improved.

1A is a diagram of a waveform of a conventional reference gamma voltage, and FIG. 1B is a diagram of a voltage configuration of a reference gamma voltage.
2 is a view schematically illustrating a pixel structure of a liquid crystal panel included in a general liquid crystal display device.
3 is a diagram illustrating a structure of a liquid crystal display according to an exemplary embodiment of the present invention.
FIG. 4A is a graph showing the relationship between luminance of each image of the image displayed by the LCD, and FIG. 4B is a graph of the frequency of each image of the image having a mosaic pattern.
5 is a diagram illustrating a structure of a timing controller in which an image compensator is built according to an exemplary embodiment of the present invention.
6 is a diagram illustrating a method of driving a liquid crystal display according to an exemplary embodiment of the present invention.

Hereinafter, a liquid crystal display and a driving method thereof according to a preferred embodiment of the present invention will be described with reference to the drawings.

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

As shown in the drawing, the liquid crystal display according to the present invention has a plurality of gate lines GL and data lines DL intersected and a pixel is defined at an intersection thereof, and a gate line GL. And a gate driver and a data driver 110 and 120 for driving the liquid crystal panel 100 through the data wiring DL, a power supply unit 140 for generating a power voltage and a common voltage for driving, and an image signal. A reference voltage generator 150 for generating a reference voltage as a conversion reference, and a timing signal and an image signal from an external system (not shown) to control a driver, and convert a gray scale range from an image signal for a specific pattern And a timing controller 160 to supply the data driver 120. The apparatus further includes a setting information storage unit 140 that stores a setting value which is a conversion reference of the gradation range when receiving a specific pattern.

In the liquid crystal panel 100, a plurality of gate lines GL and a plurality of data lines DL are arranged in a matrix form in a direction perpendicular to the gate lines GL on the transparent substrate, and a plurality of pixels at intersections. The area is defined. A thin film transistor T is formed in each pixel area, and a liquid crystal cell CLC and a storage capacitor CST controlled by the thin film transistor are configured to display a screen.

The thin film transistor T is turned on when a scan signal from the gate line GL, that is, a high potential gate voltage is applied, and applies a data voltage supplied from the data line DL to the liquid crystal cell CLC. do. In addition, the thin film transistor T is turned off when the low potential gate voltage is applied from the gate line GL to maintain the data voltage charged in the liquid crystal cell LC for one frame.

The liquid crystal cell LC represents a pixel electrode and a common electrode as a capacitor. The liquid crystal cell LC includes a common electrode facing the liquid crystal and a pixel electrode connected to the thin film transistor T. The liquid crystal cell LC is connected to the storage capacitor CST so that the charged data voltage is stably maintained until the next data voltage is charged. The pixel has a gray level by adjusting the light transmittance of the liquid crystal cell LC by changing the arrangement state of the liquid crystals according to the data voltage charged through the thin film transistor T.

In addition, a gate driver 110 including a plurality of shift registers is provided at one end of the liquid crystal panel 100 and electrically connected to the gate wiring GL formed on the liquid crystal panel 100 to sequentially gate each horizontal line. Output the drive signal.

The gate driver 110 turns on the thin film transistor T arranged on the liquid crystal panel 100 in response to the gate control signal GCS applied from the timing controller 160. The data voltage of the analog waveform supplied from the data driver 120 is applied to the liquid crystal cell CLC connected to each thin film transistor T.

As the gate control signal GCS, the gate control signal GCS includes a gate start pulse (GSP), a gate shift clock (GSC), a gate output enable (GOE), and the like. . Here, the gate start pulse GSP is a signal applied to a shift register generating the first gate pulse among the plurality of shift registers constituting the gate driver 110 to control the first gate pulse to be generated, and the gate shift clock. (GSC) is a clock signal input to all shift registers in common, and is a clock signal for shifting the gate start pulse GSP. The gate output enable (GOE) controls the output of the shift registers to prevent the thin film transistors corresponding to different horizontal sections from being overlapped and turned on.

The data driver 120 aligns the digital image signal DATA input in response to the data control signals input from the timing controller 160, and adjusts the gamma reference voltage GMA from the reference voltage generator 150. When supplied, it selects the video signal and converts it into analog data voltage. The data voltages are latched by one horizontal section 1H and are simultaneously input to the liquid crystal panel 100 through all the data lines DL. The gamma reference voltage GMA may be generated by dividing a driving voltage VDD having a predetermined level, which will be described later.

The data control signal DCS includes a source start pulse SSP, a source shift clock SSC, a source output enable (SOE), and the like. . Here, the source start pulse SSP is a signal for controlling the data sampling start timing of the data driver 120, and the source sampling clock SSC is a driving IC constituting the data driver 120 in response to a rising or falling edge. Is a clock signal that controls the sampling timing of data. In addition, the source output enable SOE controls the output timing of the data driver 120.

The gamma reference voltage generator 150 receives the driving voltage VDD from the power supply 140 to generate a plurality of gamma reference voltages GMA and supplies the same to the data driver 120.

In particular, the gamma reference voltage generator 150 may be configured of a plurality of voltage dividers (not shown) connected in series to distribute the driving voltage VDD input with a fixed voltage level from the power supply 140. Through this, a plurality of gamma reference voltages GMA are output. As shown in FIG. 1, the gamma reference voltage GMA may include a first gamma reference voltage GMA1 to a tenth gamma reference voltage GMA10.

Here, the above-mentioned divided resistance may be formed by the gamma reference voltage generator 150 in a form in which a plurality of resistors may form one resistor string, and a plurality of resistor strings are provided.

The timing controller 160 receives image data DATA applied from an external system (not shown) and timing signals such as a clock signal DCLK, a horizontal synchronization signal Hsync, and a vertical synchronization signal Vsync. A gate control signal GCS and a data control signal DCS are generated.

Here, the horizontal synchronization signal Hsync represents the time taken to display one line of the screen, and the vertical synchronization signal Vsync represents the time taken to display the screen of one frame. The clock signal DCLK is a signal for generating various signals in synchronization with the gate and data drivers 110 and 120 and the timing controller 160.

In addition, although not shown, the timing controller 160 is connected to an external system (not shown) through a predetermined interface so that the timing controller 160 receives image-related signals and timing signals outputted from the external system at high speed without error. do. As such an interface, a low voltage differential signal (LVDS) method or a transistor-transistor logic (TTL) interface method may be used.

In particular, the timing controller 160 according to an exemplary embodiment of the present invention is further connected with the setting information storage unit 170 which stores setting values for converting the gradation range according to the image pattern. In addition, the timing controller 160 includes an image compensator 150 which analyzes the image signal RGB received from an external system and changes the gradation range of the image signal by referring to the setting value stored in the setting information storage unit 170. It is built in.

The setting information storage unit 140 stores setting information which is a reference for changing the gradation range of the image signal in a lookup table (LUT) method. When the received image has a general pattern, the timing controller 160 performs alignment and conversion on the original image signal. When the received image has a specific pattern such as a mosaic pattern, the timing controller 160 refers to the setting value stored in the setting information storage unit 140. After compensating for the video signal, alignment and conversion are performed.

The setting information storage unit 140 may be implemented as a nonvolatile memory such as an electrically erasable and programmable read only memory (EEPROM).

The image compensator 180 analyzes the pattern of the image signal RGB received from an external system and processes the image range RGB according to the result to change the gradation range or to arrange and convert the original image as it is through the timing controller.

The image compensation performed by the image compensator 180 described above refers to changing the gradation range of the image signal. In the embodiment of the present invention, the saturation of the gradation, that is, the gradation value, is different by the observer. The gradation range of the video signal is reduced to the remaining parts except for the part where the difference is not recognized.

Hereinafter, a method of changing the gradation range of an image signal of an image compensator according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 4A is a graph showing the relationship between luminance of each image of the image displayed by the LCD, and FIG. 4B is a graph of the frequency of each image of the image having a mosaic pattern. Referring to FIG. 4A, as the gray scale value increases in an 8-bit 256 gray scale liquid crystal display, the luminance value increases in proportion to the gray scale value.

Here, when the image signal NP having a normal pattern is comprised between 0 gray scales (0 gray) and 245 gray scales (245 gray), the observer can easily recognize the luminance difference between the gray scales, but has a mosaic pattern. In the case of the video signal MP, at least 245 gray levels, the observer can hardly recognize the luminance difference between the gray levels. In the normally black driving LCD, 245 grayscales are close to 255 grayscale full-white. Based on this, the image compensator adjusts the maximum gray scale range of the mosaic signal from 255 grayscales to 245 grayscales. .

Table 1 below is an example of the luminance and the changed gray value according to the gray value of the image signal. The following table shows an example of a liquid crystal display having a maximum luminance of 150 cd / m ² at full-white.

No. Gradation Digital code for the original gradation value Luminance For the changed gradation value
Digital code One 0 gray 00000000 0.5 cd / m ² 00000000 2 1 gray 00000001 0.6 cd / m ² 00000001 3 2 gray 00000010 0.7 cd / m ² 00000010 128 127 gray 01111111 44.1 cd / m ² 01111111 246 245 gray 11110101 140 cd / m ² 11110101 255 254 gray 11111110 149 cd / m ² 11110101 256 255 gray 11111111 150 cd / m ² 11110101

Referring to Table 1, it can be seen that more than 245 gray levels are all changed to 11110101. This is because the difference between the gray levels is recognized by the observer in an image having a normal pattern, but is not recognized in an image having a mosaic pattern. Table 1 described above is exemplary and specific values may be differently applied according to the characteristics of the liquid crystal panel.

Hereinafter, a method of determining a pattern of an image signal by an image signal compensator according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings.

A video signal having a normal pattern appears to have irregular frequency for each gray level. However, in the video signal having a mosaic pattern, images of full-black and full-white are alternately displayed. Referring to FIG. 4B, only zero grayscale and 255 grayscale appear when the frequency of gray scales appears in the full screen. Able to know. Based on this, the image compensator calculates the frequency of the gray level for each frame with respect to the video signal received from the external system, and determines whether the image corresponds to only the 0 gray level and the 255 gray level to determine the shape of the video.

Hereinafter, a structure of a timing controller of a liquid crystal display according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

5 is a diagram illustrating a structure of a timing controller in which an image compensator is built according to an exemplary embodiment of the present invention.

As illustrated, the timing controller 160 according to an exemplary embodiment of the present invention provides a data converter 162 for arranging and converting image signals RGB and RGB ', and gate and data control signals GCS and DCS. The control signal generating unit 135 to generate and the image compensation unit 180 for changing the gray scale range by analyzing the pattern of the image signal (RGB).

The data converter 162 receives the image signals RGB and RGB 'and supplies the converted image data DATA to the data driver 120 of FIG. 3. The data driver consists of a shift register, a plurality of latches, a decoder, a level shifter, and the like, so that an original video signal (RGB) applied from an external system can be processed by the data driver. It can't be formatted. Therefore, the data converter 162 arranges and converts the data driver 162 into a form that the data driver can process and supplies the data driver.

Here, the data converter 162 receives any one of an original video signal RGB which is received from an external system and the gray scale range is not converted, and a video signal RGB 'whose gray scale range is changed by the image compensator 180. It is authorized.

The control signal generator 165 controls to control the operation timing of the gate driver and the data driver in response to timing signals such as the vertical and horizontal synchronization signals Vsync and Hsync and the clock signal DCLK input from an external system. Generate and output signals DCS and GCS.

The image compensator 180 calculates the frequency of the gray level value for each frame of the input image signal RGB to determine whether the image signal RGB corresponds to a normal pattern or a mosaic pattern. A setting value extracting unit 182 for requesting the setting information storage unit in the case of a mosaic pattern, and a gradation range changing unit 183 for changing the gradation range of the image signal RGB in response to the extracted setting value. )

The pattern discriminating unit 181 utilizes a characteristic in which grayscale values of a video signal having a normal pattern have irregular frequencies, while video signals having a mosaic pattern have only zero grayscale or 255 grayscales. The pattern discriminating unit 181 calculates a gray value for each frame of the video signal and determines a pattern of the video according to the frequency. If it is determined that the video signal has a normal pattern, the pattern determination unit 181 transfers the original video signal to the data conversion unit 162 as it is. The unit 182 transmits the original video signal.

When the image signal has a mosaic pattern, the setting value extractor 182 requests an external setting information storage unit 170 to request a changed digital code value for the gray value as shown in Table 1 above. do.

The gradation range changing unit 183 changes the gradation range of the image signal RGB in response to the extracted set value. Referring to Table 1 above, the gradation range changing unit 183 changes the digital code equal to 245 gradations for more than 246 gradations. Adjust the gradation range.

Accordingly, the gamma reference voltage generator 150 of FIG. 3 selects the reference gamma voltage according to the changed gray value to determine the data voltage, thereby changing the gray scale range.

Hereinafter, a driving method of a liquid crystal display according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings.

6 is a diagram illustrating a method of driving a liquid crystal display according to an exemplary embodiment of the present invention.

As shown, the driving method of the liquid crystal display device according to the embodiment of the present invention, the control signal and the image signal receiving step (S200), pattern determination step (S210), setting information reference step (S220), variable maximum gradation step (S230), image signal alignment and conversion step (S240) and output step (S250).

In the control signal and image data receiving step S200, the timing controller receives timing signals such as a clock signal DCLK, a horizontal synchronization signal Hsync, a vertical synchronization signal Vsync, and an image signal RGB from an external system. Step.

The pattern discrimination step (S210) is a step in which the pattern discriminator calculates a gray level value for each frame with respect to the image signal and determines the pattern of the image according to the frequency. If the pattern of the video signal is a normal pattern, the original video signal is transferred to the data converter as it is, and step S240 is performed. If it is a mosaic pattern, the original video signal is transferred to the set value extracting unit and step S220 is performed.

When the image signal has a mosaic pattern, the setting information reference step (S220) is a step of extracting a setting value for changing the gradation range by requesting the setting information storage unit.

The maximum gradation variable step S230 is a step of changing the gradation range of the image signal RGB in response to the extracted set value. For example, the gradation range is adjusted to have the same gradation value as that of the 245 gradation with respect to the gradation of 246 or more included in the video signal.

The image data sorting and converting step (S240) is a step of sorting and converting the original image signal received by the data converter or the image signal whose gradation range is changed into a form that the data driver can process according to the driving frequency.

The output step S250 is a step of outputting the aligned and converted image data to the data driver. Accordingly, the data driver converts the data driver into an analog data voltage with reference to the gamma reference voltage generator and provides the data voltage to the liquid crystal panel. The liquid crystal panel displays the gray level of the image in response to the data voltage. Here, the data voltage is applied with a data voltage lower than the potential corresponding to full-white.

Therefore, the present invention can minimize the residual defect due to the residual DC voltage by lowering the voltage level of the high potential applied to the liquid crystal cell by adjusting the gradation range for an image having a specific pattern such as a mosaic pattern.

Many details are set forth in the foregoing description but should be construed as illustrative of preferred embodiments rather than to limit the scope of the invention. Therefore, the invention should not be defined by the described embodiments, but should be defined by the claims and their equivalents.

100: liquid crystal panel 110: gate driver
120: data driver 140: power supply
150: gamma reference voltage generator 160: timing controller
170: setting information storage unit 180: image compensation unit

Claims (11)

A liquid crystal panel;
A data driver providing a data voltage to the liquid crystal panel;
Analyzing a video signal input from an external system and when the video signal has a mosaic pattern to change the gradation range from a gradation value corresponding to full-black to at least a gradation value lower than full-white to provide to the data driver A timing controller including an image compensator; And
Setting information storage unit for storing the setting value of the reference to change the gradation range
Including,
And the gradation range is changed from 246 to 255 gradations to 245 gradations. delete The method of claim 1,
The image compensator,
A gradation section discriminating unit for calculating a frequency of gradation values for each frame of the video signal, and determining a mosaic pattern when the calculated gradation values belong only to 0 gradations and 255 gradations;
A setting value extracting unit for requesting the setting information storage unit to extract the setting value if it is determined that the video signal has a mosaic pattern; And
And a gradation range changing unit for changing the gradation range of the video signal corresponding to the extracted set value from a gradation value corresponding to full-black to at least a gradation value lower than full-white. delete delete The method of claim 1,
And the setting information storage unit is an EEPROM storing the setting values in an LUT form. Receiving a timing signal and an image signal from an external system;
Analyzing the video signal and changing the grayscale value between 246 grayscales and 255 grayscales to 245 grayscale values when the video signal has a mosaic pattern; And
Arranging and converting the original video signal or the video signal whose gradation range has been changed
Method of driving a liquid crystal display device comprising a. delete The method of claim 7, wherein
When the video signal has a mosaic pattern by analyzing the video signal, changing the gradation range from a gradation value corresponding to full-black to at least a gradation value lower than full-white,
Calculating a frequency of gray values for each frame of the video signal, and determining a mosaic pattern when the calculated gray values belong to only 0 gray and 255 gray;
If it is determined that the video signal has a mosaic pattern, requesting a setting information storage unit to extract a setting value; And
And changing the gradation value between the 246 to 255 gradations to the 245 gradation value in response to the extracted set value. delete delete

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