KR101390315B1 - LCD including Discharging circuit and driving method of the same - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a driving device of a liquid crystal display device and a driving method thereof, including a discharge circuit which improves an afterimage defect occurring during power-off.

According to an embodiment of the present invention, a liquid crystal capacitor connected to a thin film transistor by supplying a discharge signal of a potential close to the gate high signal through each gate wiring of the liquid crystal panel at the time of power-off of the liquid crystal display device; The charge charged in the storage capacitor is discharged more quickly.

Therefore, it is possible to prevent a phenomenon that an afterimage remains on the screen when the LCD is turned off.

Power supply voltage VCC, gate high signal VGH, gate low signal VGL

Description

Liquid crystal display including a discharge circuit and a driving method thereof {LCD including Discharging circuit and driving method of the same}

1A is an equivalent circuit diagram of one pixel in a conventional liquid crystal display device.

FIG. 1B is a block diagram schematically illustrating a signal flow of a liquid crystal panel including a pixel of FIG. 1A, a driving circuit, and a power supply unit.

2 is a graph showing driving characteristics of a thin film transistor.

3 is a diagram illustrating an example of a discharge circuit provided in a conventionally proposed liquid crystal display device.

4 is a diagram schematically showing the structure of a liquid crystal display according to a first embodiment of the present invention.

FIG. 5 is a view showing an example of a preferable structure of the discharge circuit shown in FIG. 4 and a configuration part connected thereto.

6 is a diagram schematically showing the structure of a liquid crystal display according to a second embodiment of the present invention.

FIG. 7 is a view showing an example of a preferable structure of the discharge circuit shown in FIG. 6 and a configuration part connected thereto.

FIG. 8 is a diagram illustrating an example of a form different from the discharge circuit illustrated in FIG. 7.

<Explanation of symbols for the main parts of the drawings>

100: liquid crystal panel 120: drive circuit

130: timing controller 140: gate drive circuit

150: source driving circuit 160: power supply

180: discharge circuit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and a driving method thereof, including a discharge circuit that improves an after-image defect caused during power-off.

The liquid crystal display device has an image realization principle using optical anisotropy and polarization property of liquid crystal. As is well known, liquid crystal has a thin and long molecular structure, and when it is placed in an electric field with optical anisotropy having different refractive indices according to the arrangement direction, It has a polarization property in which the direction of arrangement changes.

Accordingly, the liquid crystal display device includes a liquid crystal panel in which a pair of substrates on which a transparent field generating electrode is formed to face each other with the liquid crystal interposed therebetween and a driving circuit provided thereon are connected to each other. The arrangement direction of the liquid crystals is artificially adjusted according to the electric field size between the two field generating electrodes.

The liquid crystal panel cross-links a plurality of X wires and Y wires in a matrix to form a pixel that is a minimum unit for expressing gray levels of an image, and sequentially supplies common voltages and data voltages to the X and Y wires, respectively. There is a passive matrix (PM) method for displaying an image, and an active matrix (AM) method for controlling each pixel individually by including a switching element in the pixel, and is currently an active matrix method. This is mainstream.

In the active matrix method, since the X and Y wirings are connected to the gate terminal and the source terminal of the switching element, the following description will be referred to as gate wiring and source wiring.

In addition, the drain terminal of the switching device is connected to the liquid crystal capacitor and the storage capacitor.

FIG. 1A is an equivalent circuit diagram of one pixel in a conventional LCD, and FIG. 1B is a block diagram schematically illustrating a signal flow of a liquid crystal panel including a pixel of FIG. 1A, a driving circuit, and a power supply unit.

The liquid crystal panel 1 includes a plurality of pixels P, and the pixels P include a gate line GL and a source line DL that cross each other, and a liquid crystal capacitor to which a common voltage Vcom is applied. Clc) and a storage capacitor Cst, a gate terminal and a source terminal are connected to the gate and source wiring GL and DL, respectively, and a drain terminal is connected to the liquid crystal capacitor Clc and the storage capacitor Cst. It consists of a transistor (TFT).

In addition, the gate and source driver circuits 4 and 5 convert a gate high signal for driving the liquid crystal panel 1 and a video signal supplied temporally and spatially to control a plurality of signal lines under the control of an external system. The data voltage corresponding to each pixel P is supplied through the pixel P.

The power supply unit 6 generates a plurality of operating voltages for driving the gate and source driving circuits 4 and 5 and supplies them to each device. In particular, the liquid crystal panel 1 supplies a common voltage Vcom supplied to the pixels. Create and supply.

Hereinafter, a driving mode according to a signal flow of a conventional liquid crystal display device will be described in detail with reference to the accompanying drawings.

First, the power supply unit 6 generates a common voltage Vcom and supplies it to the liquid crystal panel 1, and generates a power supply voltage VCC, a gate high signal VGH, and a gate low signal VGL to generate a gate driving circuit ( 4), a power supply voltage VCC, a driving voltage VDD, and a gamma voltage GMA, which is a conversion reference signal of the data signal Vdata, are generated and supplied to the source driving circuit 5.

Subsequently, when the gate high signal VGH is applied to the liquid crystal panel 1 through the gate line GL from the gate driver circuit 4, the thin film transistor TFT having the gate terminal connected to the gate line GL is formed. Is turned on. In addition, when the data signal Vdata is applied to the liquid crystal panel 1 from the source driver circuit 5 through the source wiring DL, the data signal Vdata is applied to the source terminal of each thin film transistor TFT. As a result, the voltage difference between both ends of the liquid crystal capacitor Clc connected to the drain terminal of the turned-on thin film transistor TFT is changed to change the light refractive index of the liquid crystal, thereby displaying the gray scale of the image.

Here, the data signal Vdata is applied to one end of the liquid crystal capacitor Clc, and the common voltage Vcom generated from the power supply unit 6 is applied to the other end.

Subsequently, the gate low signal VGL is applied to the liquid crystal panel 1 from the gate driver circuit 4 through the gate wiring GL to turn off the thin film transistor TFT, and thus the liquid crystal capacitor Clc is turned off. ), The charge stored in the C) may not escape through the thin film transistor TFT to maintain a voltage difference between both ends of the liquid crystal capacitor Clc for one frame. At this time, the storage capacitor Cst is charged at the same time as the liquid crystal capacitor Clc, thereby reducing the voltage drop of the liquid crystal capacitor Clc due to leakage current when the thin film transistor TFT is turned off. Gradient expression is stably displayed during the frame.

This driving is due to the driving characteristics of the thin film transistor (TFT).

FIG. 2 is a graph illustrating driving characteristics of a thin film transistor and illustrates a drain-source current I _DS according to a gate-source voltage difference V _GS .

As shown in the drawing, when the turn-on voltage V _ON is applied to the gate terminal, the corresponding turn-on current I _ON flows to the drain-source terminal so that the liquid crystal capacitor Clc is applied. To be applied).

In addition, when the turn-off voltage V _OFF is applied to the gate terminal, only the turn-off current I _OFF close to zero flows to prevent the charge applied to the storage capacitor Cst from escaping.

Such a liquid crystal display has a problem in that an afterimage remains during power-off. That is, when the power supply voltage of the driving liquid crystal display device is cut off, since the gate low signal VGL is applied to most of the gate lines GL1 to GLn, the thin film transistor TFT is turned off. Residual charges remain in the storage capacitor Cst.

In order to overcome this problem, a method of discharging the charge charged in the liquid crystal capacitor (Clc) at the time of power-off by providing a discharge circuit at the output terminal of the gate driving circuit.

3 is a diagram illustrating an example of a discharge circuit provided in a conventionally proposed liquid crystal display device.

As shown, the conventional discharge circuit 38 is composed of a capacitor C1, a diode D1, and a P-channel metal oxide silicon (PMOS) transistor. In this case, whether the power-off is detected through the capacitor C1 and the diode D1 and the ground voltage GND is applied to the gate wiring through the PMOS transistor T1 are applied to the storage capacitor (see FIG. 1). Cst) is a structure for discharging the charge charged.

This increases the drain-source current by making the gate electrode of the thin film transistor of the liquid crystal panel to the ground voltage (GND) potential during power-off. This means that the gate driving signal (VGH) for turning on the thin film transistor is turned on. The discharge speed is low because the drain-source current is smaller than when it is applied, and thus the afterimage removal rate is also slow.

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal display device including a discharge circuit for removing an afterimage generated when the liquid crystal display device is turned off and a driving method thereof.

In order to achieve the above object, the discharge circuit of the liquid crystal display according to the preferred embodiment of the present invention is a driving circuit connected to a power supply unit for supplying first to third voltages through first to third voltage terminals, respectively. An inverter having an input terminal coupled to the first voltage terminal; A first switching device connected to an output terminal of the inverter and having a source grounded; A second switching device having a gate connected to the drain of the first switching device, and a source and a drain connected to the second and third voltage terminals, respectively; A first stage is connected to the second voltage terminal and a source of the second switching element, and the second stage includes a first resistor connected to the drain of the first switching element and the gate of the second switching element. It features.

The first switching device is characterized in that the N-channel metal oxide transistor (NMOS).

The second switching device is characterized in that the P-channel metal oxide transistor (PMOS).

The first voltage may be a power supply voltage of the liquid crystal display, and the second voltage and the third voltage may be turn-on and turn-off voltages of the thin film transistor provided in the liquid crystal display, respectively.

The second switching device may further include a capacitor to which a source and one electrode are connected, and the capacitor may include another electrode grounded.

And a second resistor connected between the drain terminal of the first switching device and the gate of the second switching device.

In order to achieve the above object, a liquid crystal display device according to a preferred embodiment of the present invention, a liquid crystal including a thin film transistor, a liquid crystal capacitor and a storage capacitor connected to the thin film transistor at the intersection of the gate wiring and the data wiring. A panel; A gate driving circuit for supplying a gate high signal VGH and a gate low signal VGL which are turn-on and off signals of the thin film transistor; A source driving circuit for applying a data voltage to the liquid crystal capacitor and the storage capacitor; A discharge circuit configured to discharge the data voltage by turning on the thin film transistor in response to the power supply voltage VCC; And a power supply configured to generate the power supply voltage VCC, the gate high signal VGH, and the gate low signal VGL.

The discharge circuit is connected to the gate wiring and generates a discharge signal and supplies the thin film transistor when the power supply voltage VCC is cut off.

The discharge circuit may generate and supply a discharge signal to the thin film transistor when the power supply voltage VCC is cut off by being connected to the gate high signal VGH input terminal of the gate driving circuit.

The discharge signal is a signal having a potential smaller than the gate high signal VGH and larger than the ground voltage.

The discharge circuit may further include delay means for delaying the potential drop of the gate high signal VGH when the power supply voltage VCC is cut off.

The delay means may be a capacitor in which one electrode is grounded and the other electrode is connected to the gate high signal VGH input terminal of the discharge circuit.

In order to achieve the above object, a method of driving a liquid crystal display according to an exemplary embodiment of the present invention includes a thin film transistor provided at a point where a gate wiring and a data wiring cross, a liquid crystal capacitor connected to the thin film transistor, and storage. A liquid crystal panel including a capacitor, a gate driving circuit for supplying a gate high signal VGH as a turn-on signal and a gate low signal VGL as a turn-off signal, and a power supply voltage, A driving method of a liquid crystal display device comprising a discharge circuit for discharging a voltage charged in the liquid crystal capacitor and the storage capacitor, the method comprising: determining whether the power supply voltage is applied; Sequentially applying the gate high signal (VGH) and the gate low signal (VGL) to the thin film transistor through the gate wiring when the power supply voltage is applied; When the power supply voltage is cut off, generating a discharge signal through the gate high signal VGH to discharge the voltage charged in the liquid crystal capacitor and the storage capacitor.

When the power supply voltage is cut off, discharging the voltage charged in the liquid crystal capacitor and the storage capacitor may include: supplying the discharge signal through the gate wiring; Turning on the thin film transistor by the discharge signal; And discharging the voltages charged in the liquid crystal capacitor and the storage capacitor through the thin film transistor and the data wiring.

The discharge signal is smaller than the gate high signal VGH and has a potential higher than the ground voltage.

Hereinafter, a liquid crystal display and a driving method thereof including a discharge circuit according to a preferred embodiment of the present invention with reference to the drawings.

4 is a diagram schematically showing the structure of a liquid crystal display according to a first embodiment of the present invention.

As shown in the drawing, the liquid crystal display device according to an exemplary embodiment of the present invention converts each signal wiring by converting the liquid crystal panel 100 displaying an image largely and a video signal supplied from an external system in time and space. A driving circuit unit 120 for supplying a data voltage corresponding to each pixel through the power supply unit; a power supply unit 160 for supplying driving power to the liquid crystal panel 100 and the driving circuit unit 120; a discharge circuit 180 for discharging the pixel at the time of off.

Here, the driving circuit unit 120 receives a video signal from an external system (not shown), generates a plurality of control signals, and generates a data signal having information about an image and a timing controller 130. And a gate driver circuit 140 for enabling the liquid crystal panel 100 in horizontal lines, and a source driver circuit 150 for converting the digital data signal into an analog data voltage and supplying the liquid crystal panel 100 to the liquid crystal panel 100. It consists of

Hereinafter, the structure and operation 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.

In the liquid crystal panel 100, gate wirings GL1 to GLn formed in one direction on the substrate and source wirings DL1 to DLm intersecting with each other are arranged in a matrix form, and the liquid crystal capacitor Clc is disposed at each crossing point. And a thin film transistor (TFT), which is a switching element connected to the storage capacitor Cst. Here, a point at which the wirings intersect is defined as a pixel.

The driving circuit unit 120 receives a data signal from the gate driver circuit 140 for turning on / off the thin film transistor TFT through a plurality of gate wirings GL1 to GLn and a timing controller 130. The data driving circuit 150 generates a data voltage Vdata corresponding to the voltage GMA, and supplies the data voltage Vdata to the source electrode of the thin film transistor TFT through source wirings DL1 to DLm.

The timing controller 130 includes control signal generation means (not shown) for generating a control signal for controlling the gate driver circuit 140 and the source driver circuit 150 according to the input video signal, and the liquid crystal panel 100. And data processing means (not shown) for generating a data signal in accordance with the driving method and structure.

The power supply unit 160 includes a plurality of circuits for generating a plurality of driving voltages for operating the driving circuit 120 and a common voltage signal Vcom which is an opposite voltage of the data voltage.

In particular, the gate driver circuit 140 supplies the power supply voltage VCC, the gate high signal VGH, and the gate low signal VGL, and the source driver circuit 150 supplies the power supply voltage VCC and the drive voltage VDD. And gamma voltage (GMA).

The discharge circuit 180 detects a power-on / off state of the system by receiving a part of the signal output from the power supply unit 160, and supplies a discharge signal to the liquid crystal panel 100 accordingly. The output terminal of the supply unit 160 is connected to the gate lines GL1 to GLn.

Here, a plurality of discharge circuits 180 are connected to the gate wirings GL1 to GLn, respectively.

The operation of the liquid crystal display according to the exemplary embodiment of the present invention configured as described above is as follows.

First, when a video signal is input to the timing controller 130 from an external system (not shown), the timing controller 130 generates a control signal and a data signal in response to the video signal, and generates a gate and source driving circuit. Supply to the furnace (140, 150).

The gate driver circuit 140 sequentially turns on the thin film transistor TFT on the same horizontal line by sequentially applying the gate high signal VGH to each of the gate lines GL1 to GLn in response to the control signal.

The source driver circuit 150 simultaneously applies the data voltage Vdata corresponding to the thin film transistor TFT turned on by applying the gate high signal VGH through the data wirings DL1 to DLl. Supply to the liquid crystal capacitor (Cst) connected to the source terminal of the turned on thin film transistor (TFT).

Therefore, the liquid crystal capacitor Cst is charged with the charge corresponding to the data voltage Vdata.

In other words, an electric field is formed in the liquid crystal capacitor Cst by a voltage difference between the common voltage Vcom applied from the power supply unit 160 and the data voltage Vdata, and thus the refractive index of the liquid crystal is applied to the gray level of the image. It will change to the corresponding size.

Thereafter, the gate driving circuit 140 turns off the thin film transistor TFT by sequentially applying the gate low signal VGL through the gate wirings GL1 to GLn, and is charged in the liquid crystal capacitor Clc. The electric charge is maintained so that the gray scale of the image is displayed for one frame. In this case, the storage capacitor Cst is simultaneously charged with the liquid crystal capacitor Clc to reduce the voltage drop of the liquid crystal capacitor Clc due to leakage current when the thin film transistor TFT is turned off.

The discharge circuit 180 determines the power-on / off state of the system by sensing the magnitude of the power supply voltage VCC.

Here, the power-off state means that a plurality of voltages output from the power supply unit 160 are not supplied, and the potential changes to the level of the ground voltage after a predetermined time.

Referring to the operation of the discharge circuit 180 in more detail, the discharge circuit 180 does not operate when the system is in the power-on state, the gate supplied from the power supply unit 160 in the power-off state The discharge signal generated by the high signal VGH is supplied to the liquid crystal panel 100.

Accordingly, the discharge signal is supplied to the liquid crystal panel 100 through the gate lines GL1 to GLn and the thin film transistor TFT is turned on.

Accordingly, the charges stored in the liquid crystal capacitor Clc and the storage capacitor Cst are discharged through the data wirings DL1 to DLm as discharge paths so that the afterimage displayed on the liquid crystal panel 100 is removed at a faster time.

Hereinafter, the operation of the liquid crystal display according to the exemplary embodiment of the present invention at the time of power-off will be described in detail with reference to the drawings showing an example of the discharge circuit in detail.

FIG. 5 is a view showing an example of a preferable structure of the discharge circuit shown in FIG. 4 and a configuration part connected thereto.

As shown, the discharge circuit 180 according to the embodiment of the present invention is connected to the gate wirings GL1 to GLn of the liquid crystal panel 100 and the output terminal of the power supply unit 160.

Here, the discharge circuit 180 has an input terminal connected to the power supply unit 160, an output terminal connected to the gate wirings GL1 to GLn, and its components include an inverter I1 and a first and second transistors ( T1 and T2 and a resistor R1.

More specifically, the inverter I1 has an input terminal connected to a power supply voltage VCC terminal of the power supply unit 160 and an output terminal connected to a gate of the first transistor T1.

The source of the first transistor T1 is grounded, and the drain thereof is connected to the first node N1. The first transistor T1 is preferably an N-channel metal oxide transistor (NMOS).

In the second transistor T2, a gate is connected to the first node N1, a source is connected to the gate high signal VGH terminal of the power supply unit 160, and a drain is connected to the second node N2. The second transistor T1 is preferably a P-channel metal oxide transistor (PMOS).

The resistor R1 is connected between the drain terminal of the second transistor T2 and the first node N1.

Here, the first node N1 is defined as a point connected to the drain of the first transistor T1, the gate of the second transistor T2, and one end of the resistor R1, and the second node N2 is The drain of the second transistor T2 and a point connected to the gate wirings GL1 to GLn are defined.

Hereinafter, the operation of the discharge circuit of the liquid crystal display according to the preferred embodiment of the present invention with reference to the drawings.

At power-on, the power supply voltage VCC is input from the power supply unit 160 to the inverter I1 of the discharge circuit 180 as a logically high level, which is inverted. It is input to the gate of the first transistor T1 as a low-level. Accordingly, the first transistor T1 is turned off and the first node N1 is in a floating state.

In addition, since the first node N1 is in a floating state, the second transistor T2 also does not operate.

Subsequently, during power-off, the power supply voltage VCC is logically input from the power supply unit 160 to the inverter I1 of the discharge circuit 180 as a low level. Inverted and input to the gate of the first transistor T1 as a high-level. Accordingly, the first transistor T1 is turned on and the first node N1 has a potential of the ground voltage GND.

Accordingly, the second transistor T2 is turned on by applying the ground voltage GND and the gate high signal VGH to the gate and the source, respectively. Accordingly, the discharge signal VGH ′ is obtained by subtracting the threshold voltage V _TH of the second transistor T2 from the second node N2 connected to the drain of the second transistor T2.

Here, the second node N2 is connected to the gate lines GL1 to GLn, and thus the discharge signal VGH ′ is applied to all the gate lines GL1 to GLn.

Accordingly, all the thin film transistors TFT of the liquid crystal panel 100 are turned on to discharge charges stored in the liquid crystal capacitor Clc and the storage capacitor Cst through the data lines DL1 to DLm.

This is because the amount of drain-source current of the thin film transistor TFT is increased by supplying a signal having a higher potential than a conventional liquid crystal display device which supplies a signal having a ground voltage (GND) level to the gate wiring. The discharge drive is performed quickly.

6 is a diagram schematically showing the structure of a liquid crystal display according to a second embodiment of the present invention.

As shown in the drawing, the liquid crystal display device according to an exemplary embodiment of the present invention converts each signal wiring by converting the liquid crystal panel 200 displaying a large image and the video signal supplied from an external system in time and space. A driving circuit unit 220 for supplying data voltages corresponding to individual pixels through the power supply unit, a power supply unit 260 for supplying driving power to the liquid crystal panel 200 and the driving circuit unit 220, and a power-off power- a discharge circuit 280 for discharging the pixel at the time of off.

Here, the driving circuit unit 220 receives a video signal from an external system (not shown), generates a plurality of control signals, and generates a data signal having information about an image and a timing controller 230. And a gate driver circuit 240 for enabling the liquid crystal panel 200 in horizontal lines, and a source driver circuit 250 for converting the digital data signal into an analog data voltage and supplying the liquid crystal panel 200 to the liquid crystal panel 200. It is composed of

The liquid crystal display device according to the second embodiment of the present invention having such a structure is the same as the first embodiment described above in operation, and the following description focuses on the operation of the discharge circuit 280 at power-off. do.

The discharge circuit 280 does not operate when the system is in the power-on state. When the system is in the power-off state, the discharge circuit 280 gates the gate low signal VGL supplied from the power supply unit 260 to the gate driving circuit 240. The signal is converted to a potential close to the signal VGH and supplied to the gate driver circuit 240.

Accordingly, the output signal of the gate driver circuit 240 is supplied to the liquid crystal panel 200 through the gate wirings GL1 to GLn as the gate high signal VGH and the gate low signal VGL having a potential close thereto. (TFT) is turned on.

Accordingly, the charges stored in the liquid crystal capacitor Clc and the storage capacitor Cst are discharged through the data wirings DL1 to DLm as discharge paths so that the afterimages displayed on the liquid crystal panel 200 are removed at a faster time.

Hereinafter, the operation of the liquid crystal display according to the exemplary embodiment of the present invention at the time of power-off will be described in detail with reference to the drawings showing an example of the discharge circuit in detail.

FIG. 7 is a view showing an example of a preferable structure of the discharge circuit shown in FIG. 6 and a configuration part connected thereto.

As shown, the discharge circuit 280 according to the embodiment of the present invention, the input terminal and the power supply unit 260 of the gate driving circuit 240 connected to the liquid crystal panel 200 through the gate wiring GL1 to GLn. It is connected to the output terminal.

Here, the discharge circuit 280 has an input terminal connected to the power supply unit 260, the output terminal is connected to the gate driving circuit 240, its components are an inverter (I1), the first and second transistors (T1) , T2) and a resistor R1.

In more detail, the inverter I1 has an input terminal connected to a power supply voltage VCC terminal of the power supply unit 260 and an output terminal connected to a gate of the first transistor T1.

The source of the first transistor T1 is grounded, and the drain thereof is connected to the first node N1. The first transistor T1 is preferably an N-channel metal oxide transistor (NMOS).

In the second transistor T2, a gate is connected to the first node N1, a source is connected to a gate high signal VGH terminal of the power supply unit 260, and a drain is a gate low signal of the gate driving circuit 240. VGL) stage. The second transistor T1 is preferably a P-channel metal oxide transistor (PMOS).

The resistor R1 is connected between the drain terminal of the second transistor T2 and the first node N1.

Here, the first node N1 is defined as a point connected to the drain of the first transistor T1, the gate of the second transistor T2, and one end of the resistor R1, and the second node N2 is It is defined as a point connected to the drain of the second transistor T2 and the gate low signal VGL terminal of the gate driver circuit 240 and the power supply unit 260.

Hereinafter, the operation of the discharge circuit of the liquid crystal display according to the preferred embodiment of the present invention with reference to the drawings.

At power-on, the power supply voltage VCC is input from the power supply unit 260 to the inverter I1 of the discharge circuit 280 as a logically high level, which is inverted. It is input to the gate of the first transistor T1 as a low-level. Accordingly, the first transistor T1 is turned off and the first node N1 is in a floating state.

In addition, since the first node N1 is in a floating state, the second transistor T2 also does not operate.

Subsequently, during power-off, the power supply voltage VCC is logically inputted from the power supply unit 260 to the inverter I1 of the discharge circuit 280 at a low level. Inverted and input to the gate of the first transistor T1 as a high-level. Accordingly, the first transistor T1 is turned on and the first node N1 has a potential of the ground voltage GND.

Accordingly, the second transistor T2 is turned on by applying the ground voltage GND and the gate high signal VGH to the gate and the source, respectively. Accordingly, the discharge signal VGH ′ is obtained by subtracting the threshold voltage V _TH of the second transistor T2 from the second node N2 connected to the drain of the second transistor T2.

Here, the second node N2 is connected to the gate low signal VGL input terminal of the gate driving circuit 240. Accordingly, the second node N2 is connected to the gate lines GL1 to GLn in the state where the gate low signal VGL is applied. The discharge signal VGH 'is applied.

Of course, the gate high signal VGH is naturally applied to the gate line to which the gate high signal VGH is applied among the gate lines GL1 to GLn immediately before the power-off.

Accordingly, all the thin film transistors TFT of the liquid crystal panel 200 are turned on to discharge charges stored in the liquid crystal capacitor Clc and the storage capacitor Cst through the data lines DL1 to DLm.

In addition, although not shown, a delay means for the gate high signal VGH may be further provided for more stable driving between the power supply unit and the discharge circuit.

The delay means means that all the voltages and signals drop to the ground voltage potential over a predetermined time during the power-off of the liquid crystal display, so that the potential of the gate high signal VGH supplied from the power supply unit gradually decreases with time. .

As a result, the potential of the source terminal of the second transistor of the discharge circuit gradually decreases, so that the voltage difference between the gate and the source of the second transistor also decreases, so that the potential of the discharge signal VGH ′ applied to the gate wiring also decreases. There is a possibility that a situation arises.

In order to overcome this, it is preferable to provide a delay means between the power supply and the discharge circuit to delay the signal change of the gate high signal VGH.

The delay means may be implemented in various ways, but the proposed method includes a capacitor between the power supply and the discharge circuit.

That is, when a capacitor having one electrode grounded at the second transistor source terminal of the discharge circuit is provided, the capacitor can be discharged at power-off to delay the potential drop of the gate high signal VGH.

FIG. 8 is a diagram illustrating an example of a form different from the discharge circuit illustrated in FIG. 7.

As shown, the discharge circuit 280 according to another embodiment of the present invention, although not shown, is provided between the gate driving circuit (240 in FIG. 7) and the power supply unit (260 in FIG. 7).

Here, the discharge circuit 380 receives the power supply voltage VCC and the gate high signal VGH from the power supply unit 360 in FIG. 5, and the gate driving circuit (FIG. A discharge signal is applied to the gate low signal VGL input terminal of 240 of 7.

The configuration of the discharge circuit 380 includes an inverter I1, first and second transistors T1 and T2, and first and second resistors R1 and R2. Here, the connection form of the components is the same as the discharge circuit (280 in FIG. 7) of the second embodiment described above, except that the second resistor R2 is connected between the drain terminal of the first transistor T1 and the first node N1. This is further provided.

This is to control the voltage applied to the gate terminal of the second transistor T2, and the voltage applied to the first node N1 is determined as the ratio of the resistance values of the first and second resistors R1 and R2. do. Therefore, the output current of the second transistor T2 can be controlled more easily only by adjusting the resistance values of the first and second resistors R1 and R2.

In addition, the discharge circuit 380 of this type can be applied to the discharge circuit of the first embodiment as it is.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention as defined in the appended claims. It can be understood that

As described above, the liquid crystal display device including the discharge circuit and the driving method thereof according to the preferred embodiment of the present invention are close to the gate high signal through each gate wiring of the liquid crystal panel when the liquid crystal display device is turned off. By supplying the discharge signal of the potential, the charges charged in the liquid crystal capacitor and the storage capacitor connected to the thin film transistor are discharged more quickly.

Therefore, it is possible to prevent a phenomenon that an afterimage remains on the screen when the LCD is turned off.

Claims (15)

A driving circuit connected to a power supply unit for supplying first to third voltage through the first to third voltage terminals, respectively, An inverter having an input terminal connected to the first voltage terminal; A first switching device connected to an output terminal of the inverter and having a source grounded; A second switching device having a gate connected to the drain of the first switching device, and a source and a drain connected to the second and third voltage terminals, respectively; A first resistor connected to a first terminal of the second voltage terminal and a source of the second switching device, and a second resistor of the first terminal to a drain of the first switching device and a gate of the second switching device; Discharge circuit of the liquid crystal display device comprising a. The method of claim 1, The first switching device is an N-channel metal oxide transistor (NMOS), the discharge circuit of the liquid crystal display device. The method of claim 1, And the second switching element is a P-channel metal oxide transistor (PMOS). The method of claim 1, Wherein the first voltage is a power supply voltage of the liquid crystal display, and the second voltage and the third voltage are turn-on and turn-off voltages of the thin film transistors provided in the liquid crystal display, respectively. Circuit. The method of claim 1, The second switching device further includes a capacitor connected to a source and one electrode, wherein the capacitor is the other electrode is grounded discharge circuit of the liquid crystal display device. The method of claim 1, And a second resistor connected between the drain of the first switching element and the gate of the second switching element. A liquid crystal panel including a thin film transistor, a liquid crystal capacitor and a storage capacitor connected to the thin film transistor at a point where the gate wiring and the data wiring cross each other; A gate driving circuit for supplying a gate high signal VGH and a gate low signal VGL which are turn-on and off signals of the thin film transistor; A source driving circuit for applying a data voltage to the liquid crystal capacitor and the storage capacitor; A discharge circuit configured to discharge the data voltage by turning on the thin film transistor in response to a power supply voltage VCC; A power supply unit generating the power voltage VCC, the gate high signal VGH, and the gate low signal VGL. Including, The discharge circuit includes an inverter having an input terminal connected to the first voltage terminal; A first switching device connected to an output terminal of the inverter and having a source grounded; A second switching device having a gate connected to the drain of the first switching device, and a source and a drain connected to second and third voltage terminals, respectively; A first stage is connected to the second voltage terminal and a source of the second switching element, and a second stage includes a resistor connected to the drain of the first switching element and the gate of the second switching element. Liquid crystal display device. The method of claim 7, wherein And the discharge circuit is connected to the gate wiring and generates a discharge signal and supplies the discharge signal to the thin film transistor when the power supply voltage VCC is cut off. The method of claim 7, wherein The discharge circuit is connected to the gate high signal (VGH) input terminal of the gate driving circuit when the power supply voltage (VCC) is cut off, the liquid crystal display, characterized in that for generating and supplying a discharge signal to the thin film transistor . The method according to any one of claims 8 or 9, And the discharge signal is a signal having a potential smaller than the gate high signal (VGH) and greater than a ground voltage. The method of claim 7, wherein And the discharge circuit further comprises delay means for delaying the potential drop of the gate high signal VGH when the power supply voltage VCC is cut off. The method of claim 11, And the delay means is a capacitor in which one electrode is grounded and the other electrode is connected to a gate high signal (VGH) input terminal of the discharge circuit. A liquid crystal panel including a thin film transistor provided at a point where the gate wiring and the data wiring cross, a liquid crystal capacitor and a storage capacitor connected to the thin film transistor, a gate high signal VGH which is a turn-on signal of the thin film transistor, and And a gate driving circuit for supplying a gate-low signal VGL, which is a turn-off signal, and a discharge circuit for discharging the voltage charged in the liquid crystal capacitor and the storage capacitor in response to a power supply voltage. To Determining whether the power supply voltage is applied; Sequentially applying the gate high signal (VGH) and the gate low signal (VGL) to the thin film transistor through the gate wiring when the power supply voltage is applied; Discharging the voltage charged in the liquid crystal capacitor and the storage capacitor by generating a discharge signal through the gate high signal VGH when the power supply voltage is cut off. Including, The discharge circuit includes an inverter having an input terminal connected to the first voltage terminal; A first switching device connected to an output terminal of the inverter and having a source grounded; A second switching device having a gate connected to the drain of the first switching device, and a source and a drain connected to second and third voltage terminals, respectively; A first stage is connected to the second voltage terminal and a source of the second switching element, and a second stage includes a resistor connected to the drain of the first switching element and the gate of the second switching element. A method of driving a liquid crystal display device. 14. The method of claim 13, When the power supply voltage is cut off, discharging the voltage charged in the liquid crystal capacitor and the storage capacitor, Supplying the discharge signal through the gate wiring; Turning on the thin film transistor by the discharge signal; Discharging the voltage charged in the liquid crystal capacitor and the storage capacitor through the thin film transistor and the data wiring. A driving method of a liquid crystal display device, characterized in that. 15. The method of claim 14, And the discharge signal has a potential smaller than the gate high signal (VGH) and greater than a ground voltage.

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