KR20040057804A - Liquid Crystal Display Device And Method Of Driving Thereof - Google Patents

Abstract

PURPOSE: A liquid crystal display and a method for driving the same are provided to improve the quality of the screen since the after image displayed on the liquid crystal panel is minimized by removing the charges remaining on the insulating layer. CONSTITUTION: A liquid crystal display includes a liquid crystal panel(70), a first compensation common voltage generation part(74) and a second compensation common voltage generation part(76). The liquid crystal panel(70) is provided with a plurality of liquid crystal cells formed on the cross-sectional regions at which a plurality of data lines is crossing with a plurality of the gate lines. The first compensation common voltage generation part(74) generates a first compensation common voltage in the form of impulse applied to the liquid crystal panel(70) so as to remove the direct and positive voltage accumulated in the liquid crystal cells. And, the second compensation common voltage generation part(76) generates a second compensation common voltage obtained by correcting the first compensation common voltage level.

Description

Liquid Crystal Display Device And Method Of Driving Thereof}

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and a driving method thereof capable of removing an afterimage.

An active matrix liquid crystal display device displays a natural moving image using a thin film transistor (hereinafter, referred to as TFT) as a switching element. Such liquid crystal displays can be miniaturized compared to CRTs and are commercialized as monitors such as portable televisions, notebook computers, and laptop-type personal computers.

In an active matrix type liquid crystal display, an image corresponding to a video signal such as a television signal is displayed on a pixel matrix (pixel element) in which pixels are arranged at intersections of gate lines and data lines. Each of the pixels includes a liquid crystal cell that adjusts the amount of transmitted light according to the voltage level of the data signal from the data line. The TFT is provided at the intersection of the gate line and the data lines to switch the data signal to be transmitted to the liquid crystal cell in response to the scan signal (gate pulse) from the gate line.

Such a liquid crystal display has a twisted nematic (TN) mode in which a vertical electric field is applied according to a direction of an electric field driving a liquid crystal, and an in-plane switch having a wide viewing angle by applying a horizontal electric field. Plane Switch: hereinafter referred to as " IPS " mode.

As shown in FIG. 1, the liquid crystal display of the TN mode includes a first electrode 8 formed on the upper substrate 2 and a second electrode 6 formed on the lower substrate 4.

A third insulating layer 14 is formed on the upper substrate 2 to cover the first electrode 8, and a first insulating layer 10 is formed on the lower substrate 4 to cover the second electrode 6. do. The second insulating layer 12 is formed between the first and third insulating layers 10 and 14, and the first and second electrodes 8, 8 are disposed between the first and third insulating layers 10 and 14. The liquid crystal cell Clc is formed between 6). Here, the first and third insulating layers 10 and 14 are formed of an alignment layer and the second insulating layer 12 is formed of a liquid crystal layer.

The liquid crystal display of the IPS mode includes first and second electrodes 6 and 8 formed on the same lower substrate 4 as shown in FIG. 2.

The first insulating layer 10 is formed to cover the first and second electrodes 6 and 8, and the third insulating layer 14 is formed on the upper substrate 2 positioned to face the lower substrate 4. do. The second insulating layer 12 is formed between the first and third insulating layers 10 and 14. The liquid crystal cell Clc is formed between the first and second electrodes 6 and 8. Here, the first and third insulating layers 10 and 14 are formed of an alignment layer and the second insulating layer 12 is formed of a liquid crystal layer.

When the gate high pulse is applied to the gate electrode (not shown) of the TFT as shown in FIG. 3, the liquid crystal display of the TN mode shown in FIG. An electric field corresponding to the difference voltage between the pixel voltage and the common voltage is applied between the first and second electrodes 6 and 8 facing each other.

On the other hand, in the IPS mode liquid crystal display shown in FIG. An electric field corresponding to the difference voltage between the pixel voltage and the common voltage is applied between 6 and 8).

As such, the liquid crystals of the second insulating layer 12 are driven by horizontal or vertical electric fields to adjust the amount of light incident from the backlight.

However, in the liquid crystal display device, when the same image is displayed on the liquid crystal display device for a predetermined time, a DC voltage component is accumulated in the liquid crystal cell by a predetermined amount as the frame progresses. The DC component accumulated in the liquid crystal cell has a problem in that an afterimage is displayed on the liquid crystal display when the image is changed.

This will be described in detail with reference to FIGS. 4 and 5 as follows.

Referring to FIG. 4, the second insulating layer 12 of the TN mode liquid crystal display device is formed to have a dielectric constant different from that of the first and third insulating layers 10 and 14, so that the first and second insulating layers 10 and 12 are formed. ) And an interface is formed between the second and third insulating layers 12 and 14.

When DC voltage is applied to the first and second electrodes 8 and 6, positive charges are adsorbed to the third insulating layer 14 formed to cover the first electrode 8, and the second Negative (−) charges are adsorbed on the first insulating layer 10 formed to cover the electrode 6. The charges adsorbed to the first and third insulating layers 10 and 14 block the DC voltage applied to the second insulating layer 12 to some extent.

When the DC voltage applied from the outside is removed, the charges adsorbed to the first and third insulating layers 10 and 14 are diffused to the second insulating layer 12 having different dielectric constants and recombine with the opposite polarity charges. Even if no external voltage is applied, the DC voltage applied to the second insulating layer 12 may remain in the second insulating layer 12 due to the charge adsorbed on the first and third insulating layers 10 and 14. The residual image is displayed on the liquid crystal display by the residual DC voltage component.

Referring to FIG. 5, the second insulating layer 12 of the IPS mode liquid crystal display device is formed to have a dielectric constant different from that of the first and third insulating layers 10 and 14, so that the first and second insulating layers 10 and 12 are formed. ) And an interface is formed between the second and third insulating layers 12 and 14.

When DC voltage is applied to the first and second electrodes 8 and 6, a region corresponding to the first electrode is formed in the first insulating layer 10 formed to cover the first and second electrodes 8 and 6. Positive charges are adsorbed on the negative electrode and negative charges are absorbed in the region corresponding to the second electrode 6. The charges adsorbed on the first insulating layer 10 block the DC voltage applied to the second insulating layer 12 to some extent.

When the DC voltage applied from the outside is removed, the charges adsorbed on the first insulating layer 10 diffuse to the second insulating layer 12 having a different dielectric constant and recombine with the opposite polarity charges. Even if no external voltage is applied, the DC voltage applied to the second insulating layer 12 remains in the second insulating layer 12 because of the charge adsorbed to the first insulating layer 10. The residual image is displayed on the liquid crystal display by the residual DC voltage component.

In order to remove such residual DC voltage components, the common voltage Vcom is adjusted as shown in FIGS. 6A and 6B.

When a relatively large amount of positive residual DC voltage component A1 is accumulated in the second insulating layer 12, as shown in FIG. 6A, the positive voltage V1 + applied to the liquid crystal cell is the negative voltage V1-. The absolute value is higher by ΔV than). In this case, the absolute voltage of the positive voltage V2 + and the negative voltage V2- applied to the liquid crystal cell are the same by converting the common voltage Vcom into a compensation common voltage Vcom 'having a high potential by ΔV. Do it.

When a relatively large amount of negative residual DC voltage component A2 is accumulated in the second insulating layer 12, as shown in FIG. 6B, the negative voltage V1-applied to the liquid crystal cell is the positive voltage V1 +. The absolute value is higher by ΔV than). In this case, the absolute voltage of the positive voltage V2 + and the negative voltage V2- applied to the liquid crystal cell are the same by converting the common voltage Vcom into a compensation common voltage Vcom 'whose potential is as low as ΔV. Do it.

As described above, the TN mode liquid crystal display device is applied to the liquid crystal cell in which charges accumulated at one interface are applied to the liquid crystal cell due to the compensation common voltage Vcom 'for correcting the common voltage Vcom in the (+) or (-) direction. Since the symmetry of the negative and positive voltages can be ensured, it is relatively easy to remove the afterimage.

However, the liquid crystal display of the IPS mode has a problem that it is difficult to secure the symmetry of the negative polarity and the positive voltage applied to the liquid crystal cell because all the positive charges are accumulated at one interface as shown in FIG. 7.

Accordingly, the liquid crystal display device in the IPS mode is more likely to have an afterimage phenomenon in comparison with the liquid crystal display device in the TN mode.

Accordingly, an object of the present invention is to provide a liquid crystal display and a driving method thereof capable of removing an afterimage.

1 is a view showing a liquid crystal display of a conventional twisted nematic (Twisted Nematic).

FIG. 2 is a diagram illustrating a liquid crystal display device of a conventional in plane switch mode.

3 is a diagram illustrating a driving waveform for driving the liquid crystal display shown in FIGS. 1 and 2.

4 shows charges formed on the first and second electrodes shown in FIG.

FIG. 5 shows charges formed on the first and second electrodes shown in FIG. 2; FIG.

6A and 6B illustrate a process of compensating for a common voltage for removing an afterimage of the liquid crystal display shown in FIG. 1.

FIG. 7 is a diagram showing a residual DC voltage which is a cause of an afterimage of the liquid crystal display shown in FIG.

8 is a view showing a liquid crystal display for forming a compensation common voltage according to the present invention.

FIG. 9 is a circuit diagram illustrating a first compensation common voltage generator shown in FIG. 8. FIG.

10A and 10B are waveform diagrams illustrating a first compensation common voltage generated by the first compensation common voltage generator shown in FIG. 9;

11A to 11C are cross-sectional views illustrating a method of removing the DC voltage component remaining in the liquid crystal panel of the TN mode liquid crystal display device.

12A to 12C are cross-sectional views illustrating a method of removing the DC voltage component remaining in the liquid crystal panel of the liquid crystal display of the IPS mode.

13A to 13C are waveform diagrams illustrating a method of removing DC voltage components remaining in a liquid crystal panel using first and second compensation common voltages in the form of negative impulses.

14A to 14C are waveform diagrams illustrating a method of removing DC voltage components remaining in a liquid crystal panel using first and second compensation common voltages having positive impulse shapes.

<Description of Symbols for Main Parts of Drawings>

2,4,32,34: substrate 10,12,14,40,42,44: insulating layer

70 liquid crystal panel 72 control signal generator

74,76: Compensation common voltage generator

In order to achieve the above object, a driving method of a liquid crystal display according to an exemplary embodiment of the present invention uses an impulse type first compensation common voltage to remove any one of the positive and negative residual charges accumulated in the liquid crystal cell. And supplying the liquid crystal cell with a second compensation common voltage whose first compensation common voltage level is modulated to remove residual charges accumulated in the liquid crystal cell. do.

The first compensation common voltage is formed of a negative impulse to remove the positive residual charges, and the second compensation common voltage is lower than the first compensation common voltage to remove the negative residual charges. It is characterized in that it is formed to have.

The first compensation common voltage is formed of a positive impulse to remove the negative residual charges, and the second compensation common voltage is of a higher level than the first compensation common voltage to remove the positive residual charges. It is characterized by being formed.

The first compensation common voltage is characterized in that the impulse is formed with a pulse width similar to the gate pulse applied to the gate terminal of the liquid crystal cell.

In order to achieve the above object, the liquid crystal display according to the present invention is a liquid crystal panel in which a data line and a gate line intersect and a liquid crystal cell is formed at an intersection thereof, and the polarity DC voltage accumulated in the liquid crystal cell is removed to remove the above-mentioned voltage. A first compensation common voltage generator for generating an impulse-type first compensation common voltage applied to the liquid crystal panel, and a second compensation common voltage generator for generating a second compensation common voltage for correcting the first compensation common voltage level. Characterized in that.

And a control signal generator for controlling the first and second compensation common voltage generators.

The first compensation common voltage generator includes an operational amplifier connected between the high potential voltage source and the low potential voltage source, a first resistor connected between the inverting terminal of the operational amplifier and the input line, and between the inverting terminal and the output line of the operational amplifier. A second resistor and a first capacitor connected in parallel, a second capacitor connected between an output line and a base voltage source, a first NMOS transistor connected between a high potential voltage source and an output line, a low potential voltage source and an output line A second PMOS transistor connected between the third and third resistors, a variable resistor and a fourth resistor connected in series between the high potential voltage source and the base voltage source, and a third connected between the non-inverting terminal of the operational amplifier and the base voltage source. And a fifth resistor connected between the capacitor and the output terminal of the operational amplifier and the gate terminal of the first NMOS transistor and the second PMOS transistor. .

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. 8 to 14C.

8 is a plan view illustrating a liquid crystal display according to the present invention.

Referring to FIG. 8, in the liquid crystal display according to the present invention, a liquid crystal panel in which data lines DL1 to DLn and gate lines GL1 to GLm cross each other and a TFT for driving the liquid crystal cell Clc is formed at an intersection thereof. 70, first and second compensation common voltage generators 74 and 76 for supplying the first and second compensation common voltages PVcom to the liquid crystal panel 70, and first and second compensation common voltages. A control signal generator 72 for controlling the generator 74 is provided.

In the liquid crystal panel 70, liquid crystal is injected between two glass substrates, and the data lines DL1 to DLn and the gate lines GL1 to GLm are orthogonal to each other on the lower glass substrate. The TFT formed at the intersection of the data lines DL1 to DLn and the gate lines GL1 to GLm supplies the data on the data lines DL1 to DLn to the liquid crystal cell Clc in response to a scanning pulse. For this purpose, the gate terminals of the TFTs are connected to the gate lines GL1 to GLm, the source terminals are connected to the data lines DL1 to DLm, and the drain terminals of the TFTs are connected to the pixel electrodes of the liquid crystal cell Clc. In addition, a storage capacitor Cst is formed between the pixel electrode of the liquid crystal cell Clc and the storage line crossing the pixel electrode. The common line Vcom is applied to this storage line.

The control signal generator 72 generates a control signal CS similar to the gate output enable signal and the pulse width and the period, and supplies the same to the first and second compensation common voltage generators 74 and 76.

The first compensation common voltage generator 74 generates an impulse-type first compensation common voltage PVcom1 having a pulse width similar to that of the gate signal using the control signal CS generated by the control signal generator 72. Done.

The second compensation common voltage generation unit 76 generates a second compensation common voltage PVcom2 whose level of the first compensation common voltage PVcom1 is increased by the control signal CS generated by the control signal generation unit 72. Will generate

The first and second compensation common voltages PVcom1 and PVcom2 generated by the first and second compensation common voltage generators 74 and 76 are respectively displayed on the liquid crystal panel 70 when an afterimage is displayed on the liquid crystal panel 70. Applied to remove the afterimage. The first and second compensation common voltages PVcom1 and PVcom2 are applied to the liquid crystal panel 70 after measuring the residual image and the degree of residual image of the liquid crystal panel 70. As such, the first and second compensation common voltages PVcom1 and PVcom2 are supplied to the common electrode and the storage line of the liquid crystal panel 70 in the afterimage measurement, and in the case of normal driving, the DC voltage generated by the separate common voltage generator is generated. The common voltage is applied to the common electrode and the storage line of the liquid crystal panel 70.

As illustrated in FIG. 9, the first compensation common voltage generator 74 includes an operational amplifier OP-AMP and an operational amplifier OP− connected between a high potential voltage source VDD and a low potential voltage source VSS. The resistors R3 and R4 are disposed at the non-inverting input terminal of the AMP and the booster circuit BS is positioned at the output terminal of the operational amplifier OP-AMP.

The high potential voltage VDD divided by the third and fourth resistors R3 and R4 is input to the non-inverting (+) terminal of the operational amplifier OP-AMP, and at this time, the third and fourth resistors ( The variable resistor VR1 positioned between R3 and R4 is adjusted by the user to adjust the level of the compensation common voltage PVcom, and the third capacitor C3 serves to stabilize the power.

The control signal CS of the AC type is input to the inverting terminal (-) of the operational amplifier OP-AMP, and the output signal of the booster circuit BS is supplied to the first capacitor C1 and the first terminal R1. It is fed back through the second resistor R2 and input. The first capacitor C1 and the second resistor R2 reduce the distortion of the output voltage waveform.

The operational amplifier OP-AMP differentially amplifies a signal input to its inverting (-) terminal and the non-inverting (+) terminal and is supplied to the input terminal of the booster circuit BS through the fifth resistor R5.

The divided resistors R3 and R4 are connected in series between the high potential voltage source VDD and the ground voltage GND. The voltage divided by the voltage dividing resistors R3 and R4 is input to the non-inverting (+) terminal of the operational amplifier OP-AMP.

The booster circuit BS includes first and second switches Q1 and Q2 connected in a push-pull form, and each of the first and second switches Q1 and Q2 is implemented as an NMOS transistor and a PMOS transistor. . A second capacitor C2 for stabilizing the output voltage is positioned between the output line of the booster circuit BS and the base voltage GND.

The booster circuit BS adjusts the amounts of the high potential voltage VDD and the low potential voltage VSS supplied to at least one output line of the common electrode and the storage line in response to the voltage on the first node N1. Done. For this purpose, the gate terminals of each of the first and second switches Q1 and Q2 are connected to the first node n1. The source terminal of the first switch Q1 is connected to the high potential voltage source VDD, and the drain terminal is connected to at least one output line of the common electrode and the storage line. The source terminal of the second switch Q2 is connected to at least one output line of the common electrode and the storage line, and the drain terminal is connected to the low potential voltage source VSS.

An operation process of the first compensation common voltage generator 74 is as follows.

When the output voltage level on the first node N1 generated by the operational amplifier OP-AMP changes to be greater than or equal to the threshold voltage of the first switch Q1, the first switch Q1 is turned on and the second switch Q2 is turned on. Is turned off. Then, the high potential voltage VDD starts to be supplied to at least one output line of the common electrode and the storage line via the source terminal and the drain terminal of the first switch Q1. At this time, the level of the compensation common voltage is adjusted by the variable resistor VR1.

On the other hand, when the output voltage level on the first node N1 generated by the operational amplifier OP-AMP changes to be greater than or equal to the threshold voltage of the second switch Q2, the second switch Q2 is turned on and the first switch Q1 is turned on. Is turned off. Then, at least one output line of the common electrode and the storage line and the low potential voltage source VSS are connected to discharge the voltage on the output line to the low potential voltage VSS. As a result, the voltage on the output line of at least one of the common electrode and the storage line maintains the low potential voltage VSS.

As described above, the first compensation common voltage generation unit 74 amplifies the output signal inverted by the operational amplifier OP-AMP through the booster circuit BS and thus, the first compensation common voltage as shown in FIGS. 10A and 10B. The voltage PVcom1 is generated. The first compensation common voltage PVcom1 is applied to the liquid crystal panel 70.

11A to 13C illustrate a method of driving a liquid crystal display according to the present invention.

In the TN mode liquid crystal display illustrated in FIG. 11A, when a DC voltage is applied to the first and second electrodes 38 and 36, the third insulating layer 44 formed to cover the first electrode 38 may be provided. Positive charges are adsorbed, and negative charges are adsorbed on the first insulating layer 40 formed to cover the second electrode 36. The charges adsorbed to the first and third insulating layers 40 and 44 block the DC voltage applied to the second insulating layer 42 to some extent.

When the DC voltage applied from the outside is removed, the charges adsorbed on the first and third insulating layers 40 and 44 diffuse into the second insulating layer 42 having different dielectric constants and recombine with the opposite polarity charges. Even if no external voltage is applied, the DC voltage applied to the second insulating layer 42 remains in the second insulating layer 42 due to the charge adsorbed on the first and third insulating layers 40 and 44.

In addition, the liquid crystal display of the IPS mode illustrated in FIG. 12A is formed so as to cover the first and second electrodes 38 and 36 when a DC voltage is applied to the first and second electrodes 38 and 36. Positive charges are adsorbed to the first insulating layer 40 in the region corresponding to the first electrode 38 and negative charges to the region corresponding to the second electrode 36.

The charges adsorbed on the first insulating layer 40 block the DC voltage applied to the second insulating layer 42 to some extent. When the DC voltage applied from the outside is removed, the charges adsorbed on the first insulating layer 40 diffuse to the second insulating layer 42 having a different dielectric constant and recombine with the opposite polarity charges.

Even though there is no voltage applied from the outside, the DC voltage applied to the second insulating layer 42 remains in the second insulating layer 42 due to the charge absorbed by the first insulating layer 40. The residual image is displayed on the liquid crystal display by the residual DC voltage component.

Due to the residual DC voltage components shown in FIGS. 11A and 12A, the absolute values of the positive voltage V1 + and the negative voltage V1- applied to the liquid crystal cell are different as shown in FIG. 13A, resulting in an afterimage on the liquid crystal panel. Is formed.

In order to remove such residual DC components, the first compensation common voltage PVcom1 having a negative impulse shape is applied to the liquid crystal panel 70 as shown in FIG. 13B. The first compensation common voltage PVcom1 has a relatively narrow pulse width like a gate high pulse, causing a relatively strong discharge in a short time, and remaining in the second insulating layer 42 as shown in FIGS. 11B and 12B. Will remove the positive charges. Accordingly, the positive voltage V2 + applied to the liquid crystal cell by the negative charges remaining in the second insulating layer 42 is greater than the negative voltage V1- as shown in FIG. 13B. As small as ΔV.

Thereafter, as shown in FIG. 13C, the first compensation common voltage PVcom is converted into the second compensation common voltage PVcom2 having a low potential by ΔV. Due to the second compensation common voltage PVcom2, negative charges remaining in the second insulating layer 42 are removed as shown in FIGS. 11C and 12C. Thereby, the absolute value of the positive voltage V + and the negative voltage V- applied to the liquid crystal cell becomes equal.

As described above, the first and second compensation common voltages PVcom1 and PVcom2 compensating the common voltage Vcom may ensure symmetry of the negative and positive voltages applied to the liquid crystal cell Clc, thereby eliminating afterimages. do.

14A to 14C are diagrams illustrating a driving method of a liquid crystal display device to remove an afterimage by using a compensation common voltage signal having a positive impulse shape.

As shown in FIG. 14A, the residual DC voltage component causes an afterimage to form on the liquid crystal panel because the absolute values of the positive voltage V1 + and the negative voltage V1- applied to the liquid crystal cell are different.

In order to remove such residual DC components, as shown in FIG. 14B, the first compensation common voltage PVcom1 having a positive impulse shape is applied to the liquid crystal panel 70. The first compensation common voltage PVcom1, like the gate high pulse, has a relatively narrow pulse width, thereby causing a relatively strong discharge in a short time to remove negative charges remaining in the second insulating layer 42. Accordingly, the negative voltage V2- applied to the liquid crystal cell by the positive charges remaining in the second insulating layer 42 is smaller by ΔV than the positive voltage V1 +.

Thereafter, as shown in FIG. 14C, the first compensation common voltage PVcom1 is converted into the second compensation common voltage PVcom2 having a high potential by ΔV. Thereby, the absolute value of the positive voltage V + and the negative voltage V- applied to the liquid crystal cell becomes equal.

As described above, the first and second compensation common voltages PVcom1 and PVcom2 compensating the common voltage Vcom may ensure symmetry of the negative and positive voltages applied to the liquid crystal cell Clc, thereby eliminating afterimages. do.

As described above, the liquid crystal display and the driving method thereof according to the present invention are applied to at least one remaining in the insulating layer by applying a first compensation common voltage in the form of an impulse to the common electrode and the storage line to remove the afterimage appearing in the liquid crystal panel. One charge is removed. Thereafter, the remaining charge remaining in the insulating layer is offset by the second compensation common voltage obtained by converting the first compensation common voltage level applied to the common electrode and the storage line. As such, the residual image displayed on the liquid crystal panel may be minimized by removing electric charges remaining in the insulating layer, thereby improving 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 (7)

Supplying a first compensation common voltage in the form of an impulse to the liquid crystal cell to remove any one of the positive and negative residual charges accumulated in the liquid crystal cell; And supplying the liquid crystal cell with a second compensation common voltage whose first compensation common voltage level is modulated to remove remaining residual charges accumulated in the liquid crystal cell. The method of claim 1, The first compensation common voltage is formed of a negative impulse to remove the positive residual charges, and the second compensation common voltage is lower than the first compensation common voltage to remove the negative residual charges. A method of driving a liquid crystal display device, characterized in that it is formed to have. The method of claim 1, The first compensation common voltage is formed of a positive impulse to remove the negative residual charges, and the second compensation common voltage is of a higher level than the first compensation common voltage to remove the positive residual charges. A driving method of a liquid crystal display device, characterized in that formed. The method of claim 1, And wherein the first compensation common voltage has an impulse having a pulse width similar to a gate pulse applied to the gate terminal of the liquid crystal cell. A liquid crystal panel in which a data line and a gate line cross each other and a liquid crystal cell is formed at an intersection thereof; A first compensation common voltage generator for generating an impulse first compensation common voltage applied to the liquid crystal panel to remove the bipolar DC voltage accumulated in the liquid crystal cell; And a second compensation common voltage generation unit configured to generate a second compensation common voltage correcting the first compensation common voltage level. The method of claim 5, wherein And a control signal generator for controlling the first and second compensation common voltage generators. The method of claim 5, wherein The first compensation common voltage generator An operational amplifier connected between the high potential voltage source and the low potential voltage source, A first resistor connected between the inverting terminal of the operational amplifier and an input line; A second resistor and a first capacitor connected in parallel between the inverting terminal of the operational amplifier and an output line; A second capacitor connected between the output line and a base voltage source; A first transistor connected between the high potential voltage source and an output line; A second transistor connected between the low potential voltage source and an output line; A third resistor, a variable resistor and a fourth resistor connected in series between the high potential voltage source and the base voltage source; A third capacitor connected between the non-inverting terminal of the operational amplifier and a ground voltage source; And a fifth resistor connected between the output terminal of the operational amplifier and the gate terminals of the first and second transistors.