KR100920374B1 - Liquid crystal display and method of dirving the same - Google Patents

Abstract

The present invention relates to a liquid crystal display device capable of preventing afterimages without deteriorating image quality.

The liquid crystal display of the present invention includes liquid crystal cells formed at intersections of gate lines and data lines, a common electrode line for supplying a reference voltage from the common voltage generator to the liquid crystal cells, and a valid data supply period. A data driver for supplying a valid pixel signal to the data lines and supplying a dummy pixel signal having a discharge voltage for discharging charges remaining in the liquid crystal cells during the blank period to the data lines; And a gate driver for supplying scan pulses to at least one of the gate lines.

Description

Liquid crystal display and its driving method {LIQUID CRYSTAL DISPLAY AND METHOD OF DIRVING THE SAME}             

1 is a view showing a liquid crystal display device in a conventional in-plane switch mode.

FIG. 2 is a waveform diagram illustrating driving waveforms supplied to a common electrode line illustrated in FIG. 1.

3A and 3B are waveform diagrams showing pixel signals supplied to data lines according to an embodiment of the present invention.

4A and 4B illustrate an order in which scan pulses are supplied to gate lines in a blank period according to the first embodiment;

5A and 5B illustrate an order in which scan pulses are supplied to gate lines in a blank period according to a second embodiment;

6A and 6B illustrate an order in which scan pulses are supplied to gate lines in a blank period according to a third embodiment;

<Description of Symbols for Main Parts of Drawings>

12 liquid crystal panel 14 gate driver

16: data driver 18: common voltage generator

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device and a driving method thereof, and more particularly, to a liquid crystal display device and a driving method thereof capable of preventing afterimages without deteriorating image quality.

The liquid crystal display device displays an image by adjusting the light transmittance of the liquid crystal using an electric field. To this end, the liquid crystal display device includes a liquid crystal display panel having a liquid crystal cell matrix, and a driving circuit for driving the liquid crystal display panel.

Such a liquid crystal display device includes a twisted nematic (TN) mode for driving a liquid crystal using a vertical electric field according to a direction of an electric field for driving a liquid crystal, and an in-plane switch for driving a liquid crystal using a horizontal electric field. (Hereinafter referred to as " IPS ") mode.

The TN mode liquid crystal display is a mode in which a liquid crystal is driven by a vertical electric field between a pixel electrode and a common electrode disposed to face the upper and lower substrates, and has a large aperture ratio but a narrow viewing angle. The IPS mode is a mode in which a liquid crystal is driven by a horizontal electric field between a pixel electrode and a common electrode arranged side by side on a lower substrate, and has a large viewing angle, but a small aperture ratio.

1 is a plan view equivalently showing a conventional general IPS mode liquid crystal display.                         

Referring to FIG. 1, a conventional IPS mode liquid crystal display device includes a liquid crystal panel 12 in which liquid crystal cells are arranged in a matrix form, and a gate driver for driving gate lines GL1 to GLn of the liquid crystal panel 12. 14, the data driver 16 for driving the data lines DL1 to DLm of the liquid crystal panel 12, and the common electrode lines CL1 to CLn of the liquid crystal panel 12 in common. The common voltage supply line CCL and a common voltage generator 18 for supplying the common voltage Vcom to the common voltage supply line CCL are provided.

The liquid crystal panel 12 is connected between the thin film transistor TFT formed at each intersection of the data lines DL1 to DLm and the gate lines GL1 to GLn, and is connected between the thin film transistor TFT and the common electrode line CL. Provided liquid crystal cell.

The thin film transistor TFT is turned on when the scan signal from the gate line GL, that is, the gate high voltage VGH is supplied, and supplies the pixel signal from the data line DL to the liquid crystal cell. The thin film transistor TFT is turned off when the gate low voltage VGL is supplied from the gate line GL to maintain the pixel signal charged in the liquid crystal cell.

The liquid crystal cell includes a pixel electrode connected to the drain electrode of the thin film transistor TFT, a pixel electrode and a liquid crystal interposed therebetween, and a common electrode connected to the common electrode line CL. It is represented by liquid crystal capacitor Clc. In addition, the liquid crystal cell further includes a storage capacitor Cst formed at a portion where the pixel electrode and the common electrode overlap each other with an insulating layer therebetween so that the charged pixel signal is stably maintained until the next pixel signal is charged. The liquid crystal cell has a horizontal electric field formed by a voltage difference between the common voltage Vcom supplied to the common electrode through the common electrode line CL and the pixel signal supplied to the pixel electrode through the thin film transistor TFT. By adjusting the light transmittance by varying the arrangement of the liquid crystal cell to realize the gray scale.

The gate driver 14 sequentially supplies scan signals to the gate lines GL1 to GLn so that the thin film transistor TFT connected to the gate lines GL1 to GLn is driven in units of the gate line GL.

The data driver 16 converts the digital pixel data supplied from the timing controller (not shown) into analog pixel signals and supplies them to the data lines DL1 to DLm.

The common voltage generator 18 generates a common voltage Vcom which becomes a reference voltage when driving the liquid crystal cell, and supplies the common voltage Vcom to the common electrode lines CL1 to CLn through the common voltage supply line CCL.

When the horizontal electric field is formed by the pixel electrode and the common electrode in each of the liquid crystal cells of the conventional IPS liquid crystal display device, the charge by the horizontal electric field is accumulated in the insulating film between the pixel electrode and the common electrode. Since the driving voltage applied to the liquid crystal from the pixel electrode and the common electrode is delayed due to the charges accumulated in the insulating layer, an afterimage problem occurs in the liquid crystal display of the IPS mode.

In order to solve the afterimage problem of the IPS mode liquid crystal display device, as shown in FIG. The method has been proposed.

Referring to FIG. 2, the common voltage Vcom is lowered in the blank period BP in response to the data enable signal DE indicating the supply period of the valid pixel data and the blank period BP. The residual image problem can be solved by supplying the common voltage Vcom leveled down in the blank period BP to all liquid crystal cells through the common electrode to discharge the charges accumulated in the insulating film between the pixel electrode and the common electrode.

However, in the conventional common voltage Vcom level down method, the common voltage Vcom leveled down in the blank period BP of the previous frame (i-1) F is changed from the current frame iF to the normal voltage. When the level is increased, a predetermined delay time Δt occurs. The delay time Δt is generated by the line resistance component of the common electrode line CL formed on the liquid crystal display panel and the parasitic capacitor component between the common electrode line CL and the data line DL. Due to this delay time Δt, the common voltage Vcom is distorted at the portion where the effective pixel signal starts to be supplied to the liquid crystal panel in the current frame iF, resulting in a deterioration of image quality in which the upper portion of the screen appears relatively bright. . Furthermore, since the delay time Δt of the common voltage Vcom becomes longer when the number of liquid crystal cells is increased to display a high resolution image, the brightness at the top of the screen becomes worse.

Accordingly, an object of the present invention is to provide a liquid crystal display device and a driving method thereof capable of preventing afterimages without deteriorating image quality.

In order to achieve the above object, a liquid crystal display of the present invention includes liquid crystal cells formed at intersections of gate lines and data lines, a common electrode line for supplying a reference voltage from the common voltage generator to the liquid crystal cells; A data driver for supplying a pixel signal valid for a valid data supply period to the data lines and a dummy pixel signal having a discharge voltage for discharging charges remaining in the liquid crystal cells during the blank period to the data lines; And a gate driver for supplying scan pulses to at least one of the plurality of gate lines during the blank period.

As the dummy pixel signal, a gray voltage having a voltage level capable of discharging residual charges among a plurality of gray voltages is used.

The dummy pixel signal is selected from one of a white pixel signal and a black pixel signal.

The dummy pixel signal has one of positive and negative voltages.

Scan pulses are simultaneously supplied when scan pulses are supplied to at least two gate lines during the blank period.

The gate lines are divided into a plurality of blocks, and a scan pulse is simultaneously supplied to gate lines included in any one of the plurality of blocks in a blank period.

The gate lines are divided into a plurality of blocks, and a scan pulse is simultaneously supplied to at least one or more gate lines respectively included in the plurality of blocks in a blank period.

In the driving method of the liquid crystal display of the present invention, a valid pixel signal is supplied to a data line during a valid data supply period, a scan pulse is supplied to a gate line, and a valid pixel signal is supplied to liquid crystal cells, and a plurality of blank periods are provided during a blank period. A scan pulse is supplied to at least one of the gate lines of the gate lines, and a dummy pixel signal having a discharge voltage for discharging charges remaining in the liquid crystal cell to the data lines during the blank period is supplied. .

When the pulses are supplied to at least two gate lines during the blank period, the scan pulses are simultaneously supplied to at least two gate lines.

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

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 3A to 6B.

3A and 3B illustrate driving waveforms of the liquid crystal display according to the exemplary embodiment of the present invention.

Referring to FIG. 3A, the liquid crystal display is divided into a valid data supply period and a blank period BP due to the data enable signal DE. In the valid data supply period, an effective pixel signal is supplied to the liquid crystal cells to display a predetermined image. In the blank period BP, the dummy pixel signal is supplied to the liquid crystal cells to discharge charges accumulated in the insulating film between the pixel electrode and the common electrode. As such, when the charges accumulated in the insulating layer are removed during the blank period BP, the afterimage problem in the liquid crystal panel may be solved.

In detail, in the valid data supply period, predetermined positive and / or negative active pixel signals are supplied to the data lines by the inversion scheme. At this time, the gate lines are sequentially driven so that the effective pixel signals supplied to the data lines are supplied to the liquid crystal cells, and as a result, a predetermined image is displayed while the liquid crystal cells are driven.

In the blank period BP, a dummy pixel signal is supplied to data lines from a data driver (not shown). In addition, during the blank period BP, a scan signal is supplied from at least one gate driver to at least one of the plurality of gate lines. In this case, the negative dummy pixel signal is supplied to the liquid crystal cells connected to the gate lines receiving the scan signal. For example, when a scan signal is supplied to an i (i is a natural number) gate line, a negative dummy pixel signal is supplied to liquid crystal cells positioned on an i th horizontal line. Here, each of the liquid crystal cells supplied with the dummy pixel signal discharges the charges accumulated in the insulating film between its pixel electrode and the common electrode.

That is, in the present invention, after the dummy pixel signal is supplied to the data lines during the blank period BP, the afterimage is prevented from occurring. Therefore, in the present invention, it is possible to prevent the upper portion of the liquid crystal panel from appearing bright due to the delay of the common voltage Vcom. In other words, in the present invention, the afterimage problem can be solved without any deterioration in image quality.

On the other hand, the negative dummy pixel signal may be any gray voltage capable of discharging the charge accumulated in the insulating film of the liquid crystal cell. For example, the dummy pixel signal may be determined as either a black pixel signal or a white pixel signal.

In addition, in the present invention, as shown in FIG. 3B, a dummy pixel signal having a positive polarity capable of discharging the charges stored in the liquid crystal cell as a data line may be supplied in the blank period BP. Here, the positive dummy pixel signal may be any gray voltage capable of discharging the charge accumulated in the insulating film of the liquid crystal cell. For example, the dummy pixel signal may be determined as either a black pixel signal or a white pixel signal.

4A and 4B are diagrams illustrating an order in which scan pulses are supplied to gate lines in a blank period according to the first embodiment.

4A and 4B, the scan pulse is supplied to the first gate line GL1 in the blank period BP of the first frame. In this case, the dummy pixel signal supplied from the data lines is charged to the liquid crystal cells of the first horizontal line installed to be connected to the first gate line GL1. Therefore, the charge accumulated in the liquid crystal cells of the first horizontal line during the valid data supply period is removed by the dummy pixel signal.

Thereafter, the scan pulse is supplied to the second gate line GL2 in the blank period BP of the second frame. At this time, the dummy pixel signal supplied from the data lines is charged to the liquid crystal cells of the second horizontal line installed to be connected to the second gate line GL2. Thus, the charge accumulated in the liquid crystal cells of the second horizontal line during the valid data supply period is removed by the dummy pixel signal. That is, in the present invention, the dummy pixel signal is sequentially supplied to the liquid crystal cells formed in one horizontal line for each blank period BP to remove the accumulated charge, thereby preventing afterimages.

Meanwhile, in the present invention, scan pulses may be supplied in units of at least two gate lines GL during the blank period BP. For example, a scan pulse is supplied to the first and second gate lines GL1 and GL2 during the first blank period BP to remove charges accumulated in the liquid crystal cells of the first and second horizontal lines, and the second blank. During the period BP, scan pulses may be supplied to the third and fourth gate lines GL3 and GL4 to remove charges accumulated in the liquid crystal cells of the third and fourth horizontal lines. Subsequently, by supplying scan pulses to the two gate lines every blank period BP, the charges accumulated in the liquid crystal cells can be removed, thereby preventing the afterimage.

5A and 5B are diagrams illustrating an order in which scan pulses are supplied to gate lines in a blank period according to a second embodiment.

5A and 5B, in the second embodiment of the present invention, the gate lines GL1 to GLn are divided into blocks each including j (j is a natural number) -1 gate lines, and a blank period BP is used. Scan pulses are supplied in blocks.

In detail, the scan pulse is supplied to the gate lines GL1 to GLj-1 included in the first block in the blank period BP of the first frame. At this time, the dummy pixel signal supplied from the data line is charged to the liquid crystal cells connected to the gate lines GL1 to GLj-1, thereby removing the charge accumulated in the liquid crystal cell.

Thereafter, the scan pulse is supplied to the gate lines GLj to GL2j-1 included in the second block in the blank period BP of the second frame. In this case, the dummy pixel signal supplied from the data line is charged to the liquid crystal cells connected to the gate lines GLj to GL2j-1. At this time, the charge accumulated in the liquid crystal cell during the valid data supply period is removed. That is, in the second embodiment of the present invention, the scan pulses are supplied in block units for each blank period BP to remove charges accumulated in the liquid crystal cells.

6A and 6B illustrate a sequence in which scan pulses are supplied to gate lines in a blank period according to a third embodiment.

6A and 6B, in the third embodiment of the present invention, the gate lines GL1 to GLn are divided into blocks each including j (j is a natural number) -1 gate lines, and a blank period BP Scan pulse is supplied to at least one gate line included in each block.

In detail, the scan pulse is supplied to two gate lines GL1, GL2, GLj, GLj + 1, ... included in each block in the blank period BP of the first frame. At this time, the dummy pixel signal supplied from the data line is charged to the liquid crystal cells connected to the gate lines GL1, GL2, GLj, GLj + 1, ..., thereby removing the charge accumulated in the liquid crystal cell. .

Thereafter, the scan pulse is supplied to the gate lines GL3, GL4, GLj + 2, GLj + 3, ... included in the second block in the blank period BP of the second frame. At this time, the dummy pixel signal supplied from the data line is charged to the liquid crystal cells connected to the gate lines GL3, GL4, GLj + 2, GLj + 3, ..., and thus the charge accumulated in the liquid crystal cell Removed. That is, in the third embodiment of the present invention, the gate lines GL are divided into a plurality of blocks, and the scan pulse is sequentially applied to at least one gate line GL included in each block during the blank period BP. By supplying, charges accumulated in the liquid crystal cells are removed.

As described above, according to the liquid crystal display and the driving method thereof, the afterimage may be prevented from occurring in the liquid crystal panel by supplying the dummy pixel signal to the data lines during the blank period. In addition, in the present invention, since the dummy pixel signal is supplied to the data lines, image degradation may be prevented due to delay. That is, in the present invention, the afterimage can be improved without deterioration in image quality.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present 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.

Claims (9)

Liquid crystal cells formed at an intersection of the gate lines and the data lines; A common electrode line for supplying a reference voltage from the common voltage generator to the liquid crystal cells; A data driver for supplying a valid pixel signal to the data lines during a valid data supply period and a dummy pixel signal having a discharge voltage for discharging charges remaining in the liquid crystal cells during the blank period to the data lines; Wow, A gate driver for supplying a scan pulse to at least one of the plurality of gate lines during the blank period; The gate lines are divided into a plurality of blocks, During the blank period, scan pulses are simultaneously supplied to gate lines included in any one of the plurality of blocks, or scan pulses are simultaneously supplied to at least one or more gate lines respectively included in the plurality of blocks. A liquid crystal display device. The method of claim 1, And the gray pixel having a voltage level capable of discharging the remaining charges among the plurality of gray voltages is used as the dummy pixel signal. The method of claim 1, And the dummy pixel signal is selected from one of a white pixel signal and a black pixel signal. The method of claim 1, And the dummy pixel signal has any one of a positive voltage and a negative voltage. The method of claim 1, And the scan pulses are simultaneously supplied when the scan pulses are supplied to at least two gate lines during the blank period. delete delete A valid pixel signal is supplied to the data lines during the valid data supply period, and a scan pulse is supplied to the gate lines to supply the valid pixel signal to the liquid crystal cells; Scanning pulse is supplied to at least one of the gate lines during a blank period; Supplying a dummy pixel signal having a discharge voltage to discharge charges remaining in the liquid crystal cell to the data lines during the blank period; The gate lines are divided into a plurality of blocks, During the blank period, scan pulses are simultaneously supplied to gate lines included in any one of the plurality of blocks, or scan pulses are simultaneously supplied to at least one or more gate lines respectively included in the plurality of blocks. A method of driving a liquid crystal display device. delete

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