KR101356164B1 - Liquid crystal display device including over driving circuit - Google Patents

Abstract

The present invention relates to a technology for preventing ghosting from occurring due to overdriving in a liquid crystal display. The present invention includes a timing controller for outputting a control signal for driving the gate driver and the data driver, and including an overdriving unit to update an overdriving value for the digital video data according to a change in the frame frequency; A gate driver supplying a gate-on signal to each gate line of the liquid crystal panel; A data driver which supplies the overdriven data signal to each data line of the liquid crystal panel; It is achieved by a liquid crystal panel which is driven by the gate on signal and data signal to display an image.

Description

Liquid crystal display device including overdriving circuit

1 is an exemplary view showing that the overshoot rate is different according to the frame frequency.

2 is a block diagram of an overdriving circuit of a liquid crystal display according to the present invention;

3 is a detailed block diagram of an overdriving unit in FIG. 2;

DESCRIPTION OF THE REFERENCE SYMBOLS

21: system 22: timing controller

22A: overdriving portion 23: gate driver

24: data driver 25: liquid crystal panel

26 DC / DC converter

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for eliminating ghosting caused by overdriving in a liquid crystal display, and in particular, the ghosting phenomenon is caused by overdriving by appropriately updating an overdriving value for digital video data according to a change in frame frequency. The present invention relates to a liquid crystal display device including an overdriving circuit so as to prevent generation thereof.

In general, the liquid crystal display (LCD) has been gradually expanded to office automation equipment, audio / video equipment, and the like due to features such as light weight, thinness, and low power consumption driving.

Such a liquid crystal display device includes a liquid crystal panel driven by a data signal and a gate on signal to display an image, a gate driver supplying a gate on signal to each gate line of the liquid crystal panel, and a data line of each liquid crystal panel. And a data driver for supplying the data signal.

In addition, a storage capacitor is formed in each of the liquid crystal cells, which is formed between the pixel electrode and the front gate line of the liquid crystal cell or between the pixel electrode and the common electrode of the liquid crystal cell to maintain a constant voltage of the liquid crystal cell. Play a role.

When the turn-on signal is sequentially applied to the gate line of the liquid crystal panel, a data signal is applied to the pixel electrode of the corresponding line to display an image.

However, when the image displayed on the liquid crystal panel is a still image, it is composed of one frame, and in the case of a video, the image is represented by a plurality of sequential still images.

When the displayed image is a moving image, the liquid crystal continuously changes by the size of the data signal corresponding to each frame. For example, in order to represent a moving picture of five frames on the liquid crystal panel, since each data signal has a different size, each liquid crystal continuously changes by the size of the data signal corresponding to each frame. .

On the other hand, the magnitude of the data signal of each frame is represented by the magnitude of the gradation voltage in the liquid crystal layer so that the liquid crystal layer changes the direction of the liquid crystal molecules. Since the liquid crystal molecules have dielectric anisotropy, the liquid crystal molecules have a long axis direction. When the change is made, the dielectric constant is changed, and the gray voltage applied to the liquid crystal layer is changed by the change of the dielectric constant, and the response speed of the liquid crystal molecules of the liquid crystal layer is remarkably decreased by the change of the gray voltage.

That is, when the gradation voltage applied to the liquid crystal is changed from the gradation voltage to the high gradation voltage or vice versa, the gradation voltage of the current frame data signal is not affected by the gradation voltage of the previous frame data signal and thus does not reach the desired gradation voltage. Only after a few frames has elapsed has the data signal reached a normal gradation voltage.

For example, in the case of expressing one video composed of two consecutive frames, the liquid crystal maintains the state of being changed to the magnitude of the gray voltage corresponding to the image of the first frame, and then corresponds to the image of the second frame. If the response speed of the liquid crystal molecules decreases due to the above factors, the liquid crystal does not express the magnitude of the gray voltage corresponding to the image of the second frame within one frame time. I can't.

Such a phenomenon may be expressed as an afterimage in which the image of the first frame of the previous time is blurred on the liquid crystal display panel.

Therefore, a technique for improving the response speed of the liquid crystal molecules by overdriving the data signal for setting the gray voltage to a higher value than the normal value has been developed and applied to products.

FIG. 1 is a diagram illustrating an overshoot ratio (OSR) differently depending on a frame frequency (or frequency of a data signal) when using the same data overdriving lookup table.

For example, when the original frame frequency is changed from 120 Hz to 60 Hz, the time of one horizontal line, which is the charging time of the data signal, is reduced by half compared to when the frame frequency is 60 Hz. As a result, the overshoot rate decreases and the response speed decreases.

As another example, when the original frame frequency is lowered from 120 Hz or less, the overshoot rate is increased by that amount, which causes ghosting.

Therefore, it is necessary to appropriately adjust the amount of overdriving according to the change of the frame frequency.

Nevertheless, the conventional liquid crystal display device does not have a function of properly adjusting the amount of overdriving according to the change of the frame frequency, and thus there is a problem such that the response speed of the liquid crystal panel is reduced or a ghost phenomenon occurs. .

Accordingly, it is an object of the present invention to provide a liquid crystal display including an overdriving circuit that detects a change in the frame frequency and appropriately adjusts the amount of overdriving according to the changed frame frequency.

According to an aspect of the present invention, there is provided a timing controller configured to output a control signal for driving a gate driver and a data driver, and to detect a change in a frame frequency to update an overdriving value for digital video data; A gate driver supplying a gate-on signal to each gate line of the liquid crystal panel; A data driver which supplies the overdriven data signal to each data line of the liquid crystal panel; And a liquid crystal panel driven by the gate on signal and the data signal to display an image.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a block diagram showing an embodiment of an overdriving circuit of a liquid crystal display according to the present invention, as shown therein, a system 21 for supplying video data, a vertical / horizontal synchronization signal and a clock signal; Outputs a control signal for controlling the driving of the gate driver 23 and the data driver 24, and includes an overdriving unit to detect a change in the frame frequency to update the overdriving value for the digital video data according to the changed frame frequency. A timing controller 22 outputting the same; A gate driver 23 for supplying a gate-on signal to each gate line of the liquid crystal panel 25; A data driver 24 for supplying a data signal for overdriving in supplying the data signal to each data line of the liquid crystal panel 25; A liquid crystal panel 25 driven by a gate on signal and a data signal input from the gate driver 23 and the data driver 24 to display an image; A DC / DC converter 26 for generating various driving voltages required by the liquid crystal panel 25 was configured.

The overdriving unit of the timing controller 22 counts the gate start pulse GSP, compares the result with a preset reference value, and outputs a difference value between the leaf mode signal and the frame frequency according to the comparison result. 31); The overdriving value compensator for properly updating the original overdriving value stored in the lookup table 33 according to the output signal of the refresh rate detector 31 and outputting the updated overdriving value to the data driver 24. (32); The lookup table 33 stores an overdriving value for the data signal overdriving.

Referring to the operation of the embodiment of the present invention configured as described in detail as follows.

In the liquid crystal panel 25, m x n liquid crystal cells Clc are arranged in a matrix type. In addition, m data lines D1 to Dm and n gate lines G1 to Gn are vertically crossed in the liquid crystal panel 25, and a thin film transistor for driving the liquid crystal cell Clc at each intersection thereof is formed. TFT) is formed. The thin film transistor TFT is turned on in response to a scan pulse supplied from the gate driver 23. In this case, the data voltage on the data lines D1 to Dm is transferred to the pixel electrode of the liquid crystal cell Clc.

That is, the gate electrode of the thin film transistor TFT is connected to the same gate line G1 to Gn every horizontal line, and the source electrode of the thin film transistor TFT is the same data line D1 to Dm every vertical line. Is connected to. The drain electrode of the thin film transistor TFT is connected to the pixel electrode of each liquid crystal cell Clc.

The pixel electrodes of the liquid crystal cells Clc of each horizontal line overlap a predetermined portion with the previous gate lines G1 to Gn for driving the liquid crystal cells Clc of the previous horizontal line to form a storage capacitor. The pixel electrodes of the liquid crystal cells Clc of the horizontal line overlap a dummy gate line positioned above the first gate line G1 to form a storage capacitor Cst. The thin film transistor TFT allows the data voltage supplied to the data lines D1 to Dm to be charged to the pixel electrode in response to the gate high voltage of the scan pulses supplied to the respective gate lines G1 to Gn.

That is, the liquid crystal cells Clc have a corresponding data voltage input through the data lines D1 to Dm when the thin film transistor TFT is turned on by a gate high voltage sequentially supplied to the gate lines G1 to Gn. After charging, the charge voltage is maintained until the TFT is turned on again.

The graphics processing circuit of the system 21 converts analog data into digital video data RGB and adjusts the resolution and color temperature of the digital video data RGB. The digital video data RGB and the vertical / horizontal synchronization signal and the clock signal output from the system 21 are supplied to the timing controller 22.

The timing controller 22 controls the gate control signal GDC and the data driver 24 for controlling the gate driver 23 using the vertical / horizontal synchronization signal and the clock signal supplied from the system 21. To generate a data control signal DDC. In addition, the timing controller 22 samples the digital video data RGB input from the system 21 and rearranges the digital video data RGB to be supplied to the data driver 24.

The timing controller 22 includes an overdriving unit 22A to apply overdriving to the digital video data RGB. At this time, the overdriving unit 22A detects a change in the frame frequency to perform an overdriving function and appropriately adjusts the amount of overdriving according to the changed frame frequency.

The data driver 24 converts the digital video data RGB into a data voltage (analog gamma compensation voltage) corresponding to the gray scale value in response to the data control signal DDC from the timing controller 22. The supplied data voltage is supplied to the data lines D1 to Dm on the liquid crystal panel 25.

The gate driver 23 sequentially supplies scan pulses (gate pulses) to the gate lines G1 to Gn in response to the gate control signal GDC from the timing controller 22, thereby supplying data. Horizontal lines of the liquid crystal panel 25 are selected.

The DC / DC converter 26 generates the high potential common voltage VDD voltage, VCOM voltage, gate on (or high) voltage VGH, and gate off (or low) voltage VGL using the VCC voltage from the system 21. do.

For reference, in the above description, the data driver 24 and the gate driver 23 are separately installed from the liquid crystal panel 25. However, in recent years, each of them is COG (Chip On Glass) or COF (Chip: Chip On). There is a trend that is directly mounted on the liquid crystal panel 25 by using a packaging technology such as a film or a chip on flexible printed circuit.

Meanwhile, the operation of the overdriving unit 22A on the timing controller 22 will be described in more detail with reference to FIG. 3 as follows.

First, the refresh rate detector 31 of the overdriving unit 22A counts a gate start pulse (GSP) provided by the timing controller 22 for a predetermined time, and writes the result to EEPROM. Compare with the stored reference value. The refresh rate detector 31 outputs a refresh mode signal as '0' or '1' according to the comparison result.

The reference value pre-stored in the EEPROM refers to a count value of the frame frequency when the overdriving value for the digital video data is stored in the lookup table 33 at the previous time point, that is, the previous frame. When the refresh rate detector 31 determines that the difference value does not deviate from the preset range as a result of the comparison between the count value of the gate start pulse GSP and a reference value previously stored in the EEPROM, the digital video of the lookup table 33 is determined. Since the overdriving value for the data does not need to be updated, the refresh mode signal is output as '0'.

However, if the difference value is found to be out of the preset range, it is necessary to update the overdriving value of the lookup table 33, and outputs the refresh mode signal as '1'. A difference value, that is, a difference value of the frame frequency is output.

At this time, the overdriving value compensator 32 properly updates the overdriving value for the original digital video data stored in the lookup table 33 according to the output signal of the refresh rate detector 31 and the data driver 24. To the () side.

For example, a refresh mode signal is output as '1' by the refresh rate detector 31 while an overdriving value for digital video data is recorded on a frame frequency 110 Hz on the original lookup table 33. When the frame frequency is changed to 120 Hz and it is determined that the difference value of the frame frequency is output as '10', the overdrive value is increased by using Equation 1 below to look up to the compensated value (LUT _COMPENSATION ). The table 33 is updated and the updated overdriving value is output to the data driver 24.

[Equation 1]

'은 현재 프레임 주파수에 따라 G_Target에 가감될 값으로, M_overdrive는 리프레시모드 신호 값, Coff1 및 Coff2는 현재프레임과 이전프레임의 프레임 주파수 차이에 따른 계수값이다.Where G _Target is the original overdriving value,

'Is the value to be added to or subtracted from G _Target according to the current frame frequency, M _overdrive is the refresh mode signal value, and Coff1 and Coff2 are the coefficient values according to the difference of the frame frequency of the current frame and the previous frame.

Therefore, when the frame frequency is changed from 110 Hz to 120 Hz as described above, the time of one horizontal line, which is the charging time of the data signal, decreases correspondingly to the increased frequency value. Therefore, the coefficient value Coff1 is decreased and Coff2 is reduced. Increase.

In the state where the overdriving value is recorded based on the frame frequency 110 Hz, the refresh mode detector 31 outputs a refresh mode signal as '1', and the frame frequency is changed to 120 Hz so that the difference value of the frame frequency is '+'. If the output is found to be 10 ', the overdriving value is increased by using Equation 1 below to update the overdriving value for the digital video data of the lookup table 33 with the compensated value (LUT _COMPENSATION ). In addition, the updated overdriving value is outputted to the data driver 24.

As another example, the refresh mode signal is set to '1' in the refresh rate detector 31 while the overdriving value is recorded on the original lookup table 33 based on the frame frequency 110 Hz. If the output frequency is changed to 100Hz and the difference in the frame frequency is found to be output as '-10', the overdriving value for the digital video data is reduced by using Equation 1, and the compensated value is obtained. The lookup table 33 is updated with (LUT _COMPENSATION ), and the updated overdriving value is output to the data driver 24.

At this time, since the time of one horizontal line (1H Time), which is the charging time of the data signal, increases corresponding to the reduced frequency value, the count value Coff1 is increased and Coff2 is decreased in contrast to the above.

As described in detail above, the present invention detects a change in the frame frequency and automatically adjusts the amount of overdriving according to the changed frame frequency, so that the response speed of the liquid crystal panel decreases or a ghost phenomenon occurs due to incorrect overdriving. There is an effect that can reliably solve the problem, such as being.

Claims (5)

A liquid crystal panel for displaying an image; A gate driver supplying a gate-on signal to each gate line of the liquid crystal panel; A data driver supplying a data signal to each data line of the liquid crystal panel; A timing controller including an overdriving unit configured to output a control signal for driving the gate driver and the data driver, and to update an overdriving value for digital video data according to a change in a frame frequency, The overdriving unit, A lookup table that stores an overdriving value for digital video data of a previous frame; A refresh rate detector for comparing a count value of a frame frequency of a current frame with a pre-stored reference value and outputting a difference between a refresh mode signal and a frame frequency of the current frame and a frame frequency of a previous frame according to a comparison result; And Update or output the overdriving value of the previous frame stored in the lookup table based on a difference value between the frame frequency of the current frame and the frame frequency of a previous frame according to the refresh mode signal output from the refresh rate detector. An overdriving value compensator for outputting an overdriving value of the previous frame without And the data driver is configured to supply a data signal according to the overdriving value updated by the overdriver to the data lines as the data signal. delete The method of claim 1, And the refresh rate detector counts the gate start pulse provided from the timing controller during the frame frequency of the current frame and outputs the count value. The method of claim 1, And the reference value is a count value for a frame frequency of the previous frame. The method of claim 1, And the overdriving value compensator updates an overdriving value of the previous frame by using the following Equation.

Here, G _Target is the _overdrive value of the previous frame, M _overdrive is the refresh mode signal value, and Coff1 and Coff2 are the coefficient values according to the frequency difference between the current frame and the previous frame.

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