KR101227405B1 - LCD and driving unit and driving method thereof - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit for a liquid crystal display device and a driving method thereof for reducing abnormal display phenomena to display high quality images by improving discharge characteristics of a thin film transistor.

To this end, at least one operation signal generator for outputting an operation signal when the power of the liquid crystal display is turned off; At least one discharge circuit unit operated by receiving the operation signal and comparing one of the image signal voltages output to the respective data lines with a reference voltage and selecting and outputting one of the image signal voltages pre-output to the same data line according to the result; It provides a source driving circuit for a liquid crystal display device comprising a.

In the present invention, when the power of the liquid crystal display is turned off, each pixel of the liquid crystal display panel performing dot-inversion driving has the same discharge time so that an abnormal screen display (for example, a stray afterimage) occurs when the power is turned off. There is an effect to reduce the.

Description

Driving circuit, driving method thereof, and liquid crystal display device having the same

1 is a block diagram showing the configuration of a conventional liquid crystal display device

2 is a diagram illustrating a discharge path through which charges Q charged in a liquid crystal display panel pixel pass through a thin film transistor TFT;

3 is a diagram showing pixel driving polarity of a liquid crystal display panel of two dot-inversion driving;

4 is a diagram illustrating a voltage charged in the positive and negative pixels illustrated in FIG. 3.

FIG. 5 is a diagram illustrating an after-image of a screen stripe generated by a charging voltage of a driving pixel illustrated in FIG. 4.

6 is a block diagram showing the configuration of a source driving circuit for a liquid crystal display according to the present invention.

7 is a diagram illustrating an operation signal generator application circuit of a source driving circuit according to the present invention;

8 is a view showing a discharge circuit application circuit of the source driving circuit according to the present invention;

9 is a flowchart illustrating the operation of the source driving circuit according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

100: source driving circuit 110: the first MUX unit

120: latch portion 130: P / N decoder portion

140: second MUX unit 150: operation signal generation unit

160: discharge circuit POL: polarity inversion signal

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device, and more particularly, to a liquid crystal display device driving circuit and a driving circuit for reducing the abnormal display phenomenon to display a high quality image by improving the discharge characteristics of the thin film transistor when the liquid crystal display panel is turned off. It is about a method.

Among display devices, liquid crystal display devices have advantages of small size, thinness and low power consumption and are used in notebook computers, office automation devices, audio / video devices, and the like. In particular, an active matrix type liquid crystal display device using a thin film transistor (hereinafter referred to as "TFT") as a switching element is suitable for displaying dynamic images.

FIG. 1 is a block diagram showing the structure of a conventional liquid crystal display device, and shows a liquid crystal panel 2, a source driver circuit D, and a scan driver circuit S. As shown in FIG.

The liquid crystal panel 2 forms a plurality of pixel regions by crossing a plurality of data lines DL1 to DLm and a plurality of scan lines GL1 to GLn on a glass substrate. The thin film transistor TFT, the liquid crystal Clc, and the storage capacitor Cst are configured to display a screen.

The source driving circuit (D) is of an integrated chip (IC) type, receives a control signal, selects reference voltages of the image signals, and supplies the selected reference voltage to the liquid crystal panel 2 to control the rotation angle of the liquid crystal molecules. do.

The scan driving circuit S is also an IC type, and receives a control signal to perform on / off control of thin film transistors TFTs arranged on the liquid crystal panel 2. By sequentially enabling the scan lines GL1 to GLn by one horizontal synchronizing time, the thin film transistors TFT on the liquid crystal panel 2 are sequentially driven one by one line from the source driver circuit D. The supplied analog image signals are applied to the liquid crystal Clc connected to each thin film transistor TFT.

When each pixel of the liquid crystal display having the above configuration is turned off, as shown in a dotted line in FIG. 2, the charges Q charged in each pixel pass through the thin film transistor TFT. Discharge paths are transferred to the lines DL1 to DLm and the source driving circuit D.

However, since the channel of the TFT is closed as the power is turned off, the charged charge Q is gradually discharged. In particular, in the dot-inversion method, the positive polarity divided by the common voltage Vcom (+) Since the level of the input voltage between the pixel of the field) driving and the pixel of the negative (-field) driving is different from each other, the time required for discharge is also different between the polarities of the pixels.

In particular, in the two-dot inversion driving liquid crystal display as shown in FIG. 3, the discharge time is also different due to different input voltage levels between the positive and negative pixels, as illustrated in the pixel charging voltage example of FIG. 4. This causes a problem that afterimages of different levels of shadows remain on the screen as shown in FIG. 5 to be recognized as screen stripes.

Such stripes are more clearly recognized in the 2X2 dot-inversion driving liquid crystal display device of the dot-inversion driving liquid crystal display device.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to equalize the discharge time for each pixel that is different due to different image signal voltage levels between adjacent pixels when the LCD is turned off. Accordingly, the object of the present invention is to provide a high-quality liquid crystal display device by removing screen streaks generated when the LCD is turned off.

In order to achieve the above object, according to the present invention, a plurality of data lines and a plurality of scan lines are formed, and a positive display pixel and a voltage lower than a common voltage to which a first image signal having a voltage level higher than a common voltage are input. A driving circuit of a liquid crystal display device having a liquid crystal display panel which is divided into a negative display pixel into which a second image signal having a level is input and the polarity of the image signal input to each display pixel is inverted every frame. At least one operation signal generator for outputting an operation signal at the moment when the power of the display device is turned off; At least one discharge circuit unit operated by receiving the operation signal and comparing one of the image signal voltages output to the respective data lines with a reference voltage and selecting and outputting one of the image signal voltages pre-output to the same data line according to the result; It provides a source driving circuit for a liquid crystal display device comprising a.

The liquid crystal display panel is characterized in that the dot inversion driving is performed.

The operation signal generator is characterized in that the inverter.

The discharge circuit unit is a comparator, and the reference voltage is characterized in that the common voltage.

The discharge circuit unit outputs the first image signal pre-output to the same data line when the image signal voltage output to each data line is lower than the reference voltage, and the image signal voltage output to each data line is the reference. When the voltage is higher than the voltage, the second image signal pre-outputted to the same data line is output.

In addition, the present invention, the timing control unit for outputting the digital image data and a plurality of control signals; A plurality of liquid crystal pixels are formed in an area where the plurality of data lines and the plurality of scan lines cross each other, and the plurality of liquid crystal pixels are divided into a positive display pixel and a negative display pixel; A gate driver which sequentially outputs scan signals to the plurality of scan lines according to the control signal; In response to the scan signal, an analog image signal is output to the plurality of data lines, and when the power is turned off, the image signal voltage output to each data line is compared with a reference voltage and pre-outputted to the same data line according to the result. Provided is a liquid crystal display including a source driver for selecting and outputting one of image signal voltages.

The video signal is characterized in that the RGB data.

The liquid crystal display panel may be a display panel on which inversion driving is performed.

The source driver outputs the first image signal pre-output to the same data line when the image signal voltage output to each data line is lower than the reference voltage, and the image signal voltage output to each data line is the reference. When the voltage is higher than the voltage, the second image signal pre-outputted to the same data line is output.

In addition, the present invention, the step of detecting whether the power supplied to the liquid crystal display device; It is operated when the power is off, and provides a driving method of the source driving circuit for a liquid crystal display device comprising comparing the output image signal and the reference voltage and outputs one of the pre-output image signal according to the result.

When the output image signal voltage is lower than the reference voltage, the output image signal of a voltage level higher than the reference voltage among the pre-output image signals, and when the output image signal voltage is higher than the reference voltage, the pre-output image And outputting an image signal having a voltage level lower than the reference voltage among the signals.

Hereinafter, the present invention will be described with reference to the accompanying drawings.

6 is a block diagram showing the configuration of the source driving circuit 100 for the liquid crystal display device according to the present invention.

Referring to the configuration, the operation signal generator 150 is applied to a conventional source driving circuit configuration that receives digital RGB data and outputs analog RGB data to a liquid crystal display panel (not shown) after polarity conversion according to the polarity inversion signal POL. And a discharge circuit unit 160.

The first MUX unit 110 includes a plurality of MUX circuits to receive digital RGB data from an external circuit (for example, a timing controller), and the digital RGB data input to the MUX circuit selected according to the polarity inversion signal POL. Is entered.

The latch unit 120 includes a plurality of latch circuits, and receives and latches the RGB data output from the first MUX unit 110 and outputs the latch data.

The P / N decoder 130 receives the digital RGB data output from the latch unit 120 and decodes the analog RGB data, and determines the polarity of the output data for dot-inversion driving. In this case, the polarity of the data is determined based on the common voltage Vcom of the liquid crystal display panel. When the data polarity is higher than the common voltage Vcom, the polarity of the data is negative.

The second MUX unit 140 includes a plurality of MUX circuits, and receives the RGB data decoded by the P / N decoder unit 130 and outputs the RGB data to the LCD panel.

The operation signal generator 150 is a circuit unit that outputs a set signal (hereinafter, the operation signal DS) when the driving voltage Vcc supplied to the liquid crystal display panel (or liquid crystal display device) is turned off. For example, when the driving voltage Vcc is turned off using an inverter (that is, a NOT gate) receiving the driving voltage Vcc as shown in FIG. 7, an operation signal of "high level" or logic "1" ( Output DS). The inverter circuit may be configured at each output terminal (not shown) of the source driving circuit 100 and may be configured only one.

 The discharge circuit unit 160 is a circuit operated by receiving the operation signal DS from the operation signal generator 150 when the liquid crystal display panel is turned off, and controls the data voltage Vi output to each data line of the liquid crystal display panel. Select the positive (+ field) data (hereinafter referred to as first voltage (+ E)) or the negative (-field) data (hereinafter referred to as second voltage (-E)) pre-output to the same data line according to the voltage level. Output to each data line.

Referring to FIG. 8, the discharge circuit unit 150 will be described in more detail. The device applied to the discharge circuit unit 160 is preferably a saturation comparator, and receives the operation signal DS and drives the drive signal DS. To start.

The output voltage (Vout) of the discharge circuit unit 160 is the first voltage (+ E) or the second voltage (-E), the non-inverting terminal (+) to which the reference voltage (Verf) is input, the liquid crystal display The common voltage Vcom supplied to each pixel of the panel is input, and the data voltage Vi output to the liquid crystal display panel is input to the inverting terminal (−). In this case, when the data voltage Vi is negative data, the first voltage + E is output to the liquid crystal panel, and when the data voltage Vi is positive data, the second voltage is positive. The voltage (-E) is output to the liquid crystal display panel. The discharge circuit unit 160 that performs the above driving is configured at each output terminal of the source driving circuit 100 so as to affect all the driving pixels of the liquid crystal display panel according to the operation thereof. That is, the number of data lines through which data is transferred is configured at each output terminal of the source driving circuit 100.

Hereinafter, an operation of the source driving circuit according to the present invention configured as described above will be described with reference to the flowchart of FIG. 9.

The digital RGB data and the polarity inversion signal POL are input to the source driving circuit 100 according to the present invention, and the digital RGB data is polarized in accordance with the dot-inversion by the polarity inversion signal POL. The transfer paths to the plurality of MUX circuits configured in the first MUX unit 110 and the plurality of latch circuits configured in the latch unit 120 are selected, and then through the first MUX unit 110 and the latch unit 120. The output digital RGB data is input to the P / N decoder unit 130, converted into analog RGB data, and output to the liquid crystal display panel through the second MUX unit 140 (S1).

When the power of the liquid crystal display is turned off while the driving is performed, the driving voltage Vcc of the liquid crystal display drops, and thus an inverter (NOT gate) of the operation signal generator 150 generates an operation signal. (DS) That is, a high level signal or a "1" logic signal is output. (S2)

The discharge circuit unit 160 receiving the operation signal DS is driven, and the comparator composed of the discharge circuit unit 160 receives the data voltage Vi of the source driving circuit 100 output to the liquid crystal display panel. Compared with the common voltage Vcom, which is a reference voltage Vref (S3), and as a result, when the data voltage Vi is higher than the common voltage Vcom, the second data, which is negative data, pre-output to the same data line. When the data voltage Vi is lower than the common voltage Vcom, the first voltage + E, which is positive polarity data pre-output to the same data line, is output. That is, when the common voltage Vcom for driving the pixel of the liquid crystal display panel is 3V, the first voltage (+ E) pre-output to the Mth data line is 5V, and the second voltage (-E) is 1V. When the output data voltage Vi is 2V, the first voltage 5V is output to the same M-th data line. When the output data voltage Vi is 4V, the second voltage 1V is output to the same Mth data line.

The driving is performed at each output terminal of the source driving circuit 100. In the liquid crystal display device which is driven by the scan signal output and the data output for a predetermined time even after the power supply Vcc is turned off, the output is performed after the power supply Vcc is turned off. The first voltage (+ E) or the second voltage (-E) pre-output to the same data line according to the level of the data voltage (Vi) is input to each pixel in accordance with the scan signal output period, so that each In the data line, since the voltage of the positive pixel and the voltage of the negative pixel become the same for each polarity, the discharge time between the positive (+) driving pixel and the negative (-) driving pixel is the same, and the screen when the power is turned off Streaks are not recognized on the image.

As described above, the source driving circuit and the driving method thereof according to the present invention, when the power supply of the liquid crystal display device is turned off, each pixel of the liquid crystal display panel performing dot-inversion driving has the same discharge time, so that when the power off There is an effect of reducing the occurrence of abnormal screen display (e.g., streaks of afterimage) that occur.

Claims (11)

A plurality of data lines and a plurality of scan lines are formed, and a positive display pixel to which a first image signal having a voltage level higher than the common voltage is input and a negative polarity to which a second image signal having a voltage level lower than the common voltage are input. A driving circuit of a liquid crystal display device having a liquid crystal display panel, which is divided into display pixels, and the polarity of an image signal input to each display pixel is inverted every frame. At least one operation signal generator for outputting an operation signal when the power of the liquid crystal display is turned off; At least one discharge circuit unit operated by receiving the operation signal and comparing one of the image signal voltages output to the respective data lines with a reference voltage and selecting and outputting one of the image signal voltages pre-output to the same data line according to the result; Including; The discharge circuit unit outputs the first image signal pre-output to the same data line when the image signal voltage output to each data line is lower than the reference voltage, and the image signal voltage output to each data line is the reference. When the voltage is higher than the voltage source driving circuit for the liquid crystal display device characterized in that for outputting the second image signal pre-output to the same data line The method according to claim 1, The liquid crystal display panel is a source driving circuit for the liquid crystal display device characterized in that the dot inversion driving is performed The method according to claim 1, The operation signal generator is an inverter; The method according to claim 1, And the discharge circuit portion is a comparator, and the reference voltage is the common voltage. delete A timing controller for outputting digital image data and a plurality of control signals; A plurality of liquid crystal pixels are formed in an area where the plurality of data lines and the plurality of scan lines cross each other, and the plurality of liquid crystal pixels are divided into a positive display pixel and a negative display pixel; A gate driver which sequentially outputs scan signals to the plurality of scan lines according to the control signal; The analog image signal is output to the plurality of data lines in synchronization with the scan signal, and when the power is turned off, the image signal voltage output to each of the data lines is compared with a reference voltage and pre-outputted to the same data line according to the result. A source driver which selects and outputs one of the image signal voltages, The source driver outputs a first image signal pre-output to the same data line when the image signal voltage output to each data line is lower than the reference voltage, and the image signal voltage output to each data line is the reference voltage. If it is higher than the liquid crystal display characterized in that for outputting the second image signal pre-output to the same data line The method of claim 6, And the video signal is RGB data. The method of claim 6, The liquid crystal display panel is a display panel in which inversion driving is performed. delete Detecting whether the power supplied to the liquid crystal display is turned off; Operating when the power is off, comparing the output image signal with a reference voltage and outputting one of the pre-output image signals according to the result; When the output image signal voltage is lower than the reference voltage, the output image signal of a voltage level higher than the reference voltage among the pre-output image signals, and when the output image signal voltage is higher than the reference voltage, the pre-output image A method of driving a source driving circuit for a liquid crystal display device, characterized by outputting an image signal having a voltage level lower than the reference voltage among the signals. delete

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