KR101003694B1 - Driving unit of liquid crystal display - Google Patents

Abstract

The present invention relates to a driving unit of a liquid crystal display device, wherein the driving unit of the liquid crystal display device of the present invention selects a gray voltage corresponding to image information and outputs the pixel voltage as a pixel voltage, and a pixel voltage generated at a falling edge of a scan signal. And selectively outputs a compensation voltage for compensating for the variation of the voltage, and applies the compensation voltage before the falling edge of the scan signal to charge the pixel voltage before applying the compensation voltage and the voltage level of the pixel voltage. A voltage compensator for compensating for the variation of the pixel voltage to be equal to a voltage level, a first charger for charging with the gray voltage of the gray voltage part, and a second charger for charging with a compensation voltage of the voltage compensator; The gray voltage unit and the first charging unit electrically connected to each other according to a control signal, Charge the first charging unit and cut off the output or cut off the connection of the gradation voltage unit and the first charging unit and electrically connect the first charging unit and the output to receive the gradation voltage charged in the first charging unit. The output is cut off according to the first switching unit and the second control signal to be output and electrically connected to the voltage compensating unit and the second charging unit, and the compensation voltage of the voltage compensating unit is charged to the second charging unit or the voltage compensation is performed. And a second switching unit which cuts off the connection between the unit and the second charging unit and outputs the compensation voltage charged in the second charging unit.

Voltage drop, gradation voltage, coupling, scan signal, R-STRING

Description

DRIVING UNIT OF LIQUID CRYSTAL DISPLAY}

1 is a diagram showing a digital-analog conversion circuit using R-STRING.

2 is a waveform diagram showing driving of image information according to a scanning signal in a pixel;

3 is a view briefly showing charging characteristics of a pixel;

4 is a waveform diagram showing a relationship between a scan signal and a pixel voltage according to a high potential scan signal conversion (Vgh modulation) method;

5 is a block diagram of a driving unit of the liquid crystal display according to the first embodiment of the present invention.

FIG. 6 is a block diagram of the liquid crystal display driver shown in FIG. 5 in an equivalent circuit; FIG.

7 is a waveform diagram showing an operating waveform of a driving unit of a liquid crystal display according to a first embodiment of the present invention;

DESCRIPTION OF REFERENCE NUMERALS

100,200: gradation voltage section 102,202: voltage compensation section

111: first switching unit 112: first charging unit

121: second switching unit 122: second charging unit

SOE: first control signal VP_C: second control signal

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving unit of a liquid crystal display, and more particularly, to a driving unit of a liquid crystal display device for compensating image information dropped when the potential of the scan signal changes.

In general, a liquid crystal display device is a thin film transistor array substrate and a color filter substrate facing each other are bonded at regular intervals, the liquid crystal display device in a space spaced between the thin film transistor array substrate and the color filter substrate A liquid crystal display panel (Liquid Crystal Display Panel) formed with a liquid crystal layer and a driving unit for supplying a scan signal and image information to the liquid crystal panel to drive the liquid crystal panel.

In the liquid crystal display panel, a plurality of gate lines arranged to be horizontally spaced apart from each other and a plurality of data lines arranged to be vertically spaced apart from each other cross each other, and a quadrangle in which the gate lines and the data lines cross each other and are partitioned. Pixels are formed in the area.

In addition, a color filter of red, green, and blue is formed at a position corresponding to the pixels on the color filter substrate, and a black matrix for preventing color interference of light passing through the color filter includes the color matrix. The common electrode is formed in a net shape surrounding the outside of the filter and applies an electric field to the liquid crystal layer together with the pixel electrode of the thin film transistor array substrate.

A pixel electrode and a common electrode are provided on an inner surface of the thin film transistor array substrate and the color filter substrate so that the liquid crystal is driven by the voltage difference between the pixel electrode and the common electrode, and the size of the image information applied to the pixels. Accordingly, the luminance of the image displayed on the liquid crystal display panel is changed.

Switching elements such as thin film transistors are individually provided in the pixels, wherein a gate electrode of the thin film transistor is electrically connected to the gate lines, a source electrode is electrically connected to the data lines, and a drain electrode. Is electrically connected to a pixel electrode provided in the pixel, the source electrode receives image information through the data lines, and the image information is applied to the pixel electrode through the drain electrode. A voltage difference is generated between them, and the liquid crystal is driven.

The driving unit sequentially applies a scanning signal to the gate lines every frame to the liquid crystal display panel, and applies image information to the pixel through the data lines in response to the scanning signal of the gate driving unit. It consists of a data driver.

The gate driver sequentially applies a scan signal to the gate lines every frame unit. At this time, the switching elements having a gate electrode electrically connected to the gate line to which the scan signal is applied are turned on, and the image information supplied from the data driver to the data lines is applied to the scan signal. Is applied to the pixel via the switching element turned on.

In recent years, the image medium is easy to compress the information to provide a high-quality image to viewers, and mainly uses a digital image information that can implement a large-capacity and high-quality image information. The liquid crystal display also displays an image on the screen by digital image information. However, due to the characteristics of the liquid crystal display device which drives the liquid crystal due to the voltage difference between the pixel electrode and the common electrode, the digital image information cannot be directly used. The liquid crystal is driven by converting the digital image information into analog image information. This conversion is called digital-analog convert (DAC).

If the digital image information includes 4 bits of information, 2 ⁴ = 16 gradations, that is, 16 kinds of luminance can be expressed. As such, there is a method of using R-STRING to convert image information in the form of a plurality of bits into a voltage capable of driving a liquid crystal. The R-STRING method is a method of connecting a plurality of resistors in series, dropping a power supply voltage by the plurality of resistors, and selecting and applying a voltage corresponding to a bit value of digital image information to a pixel.

The R-STRING digital-analog conversion scheme as described above will be described in detail with reference to the accompanying drawings.

1 is a diagram illustrating a digital-analog conversion circuit using R-STRING.

Referring to Fig. 1, as an R-STRING for converting 4-bit image information, it is an R-STRING structure for converting 4-bit digital image information to a voltage of 16 gradations.

First, the first decoder 30 and the second decoder 31 for decoding 4-bit image information by 2 bits, and the data switching element selectively turned on by the second decoder 31 ( S1 to S4 and a plurality of resistors connected in series to drop the power supply voltage VCC in order, and individually connected to the plurality of resistors to determine application and blocking of each gradation voltage. A plurality of switching elements, a plurality of word lines to which a signal is selectively applied by the first decoder 30, and a plurality of bits to which a signal is selectively applied by the second decoder 31 A plurality of lines driven by lines and a source output enable (SOE) signal to charge image information to a capacitor C1 and to apply a gray voltage charged to the pixel to the pixel. It comprises a switch (SW1, SW2).

The plurality of resistors are not arranged in a line, but are arranged in a folded state by four in a line. The image information obtained by dividing each bit by two bits into the 4 × 4 type resistor array is divided into the first decoder 30 and the second decoder 31 and applied.

The first decoder 30 applies a signal by selecting one line among four lines of word lines arranged laterally by two-bit image information input, and switching connected to the selected word line. The device receives a signal through the gate electrode and is turned on. In addition, the second decoder 31 selects one line among four lines of bit lines arranged vertically by two-bit image information received, and selects a switching device connected to the selected line ( S1 to S4 are turned on and a gray voltage is applied through the drain electrode of the corresponding switching element among the switching elements of the word line selected by the first decoder 30. As such, one of the plurality of gray voltages formed through the R-STRING is selected by the first decoder 30 and the second decoder 31.

When the SOE signal is low, the charge switch SW1 is turned on, connected to the R-STRING side point A1, and the supply switch SW2 is turned off. The pixel side point A2 is cut off, and the gray level voltage selected by the first decoder 30 and the second decoder 31 is applied through the charging switch SW1 to charge the capacitor C1. When the SOE signal is in the high state, the charging switch SW1 is turned off to be cut off from the R-STRING side point A1, and the supply switch SW2 is turned off. Is connected to the pixel side point A2, and the image information charged in the capacitor C1 is outputted to the pixel.

2 is a waveform diagram illustrating driving of image information according to a scanning signal in a pixel.

When a constant electric field is continuously applied to the liquid crystal layer of the liquid crystal display device, the liquid crystal deteriorates, resulting in afterimages generated by the DC voltage component. Therefore, in order to prevent deterioration of the liquid crystal and to remove the DC voltage component, the voltage of the image information is applied to the positive and negative repetition based on the common voltage. This driving method is called an inversion method.

The inversion driving method includes a frame inversion method in which the polarity of the image information is inverted by one frame unit of the image, a line inversion method in which the polarity of the image information is inverted and supplied in the gate line unit, and image information. There is a dot inversion scheme in which the polarities of are inverted and supplied for each adjacent pixel and are inverted and supplied in units of one frame of the image.

Referring to FIG. 2, the scan signal VG is sequentially applied to the gate line every frame, and the common voltage VCOM applied to the common electrode is applied to a DC voltage having a constant level. Then, the voltage VP1 of the image information VDATA is driven in an inversion manner based on the common voltage VCOM.

In the turn-on period of the thin film transistor to which the scan signal VG is applied at high potential, the image information VDATA applied to the pixel electrode is charged in a storage capacitor, which is represented by the pixel voltage VP1 waveform shown. .

In addition, when the scan signal VG transitions to a low potential, that is, at the falling edge of the scan signal VG, the parasitic capacitance according to the over-lap of the gate electrode and the source electrode of the thin film transistor is measured. A voltage drop occurs from the pixel voltage VP1 due to a coupling phenomenon, which is called a variation ΔVP1 of the pixel voltage.

The pixel voltage VP1 drives the liquid crystal by the voltage difference VCEL1 from the common voltage VCOM.

Meanwhile, in the turn-off period of the thin film transistor to which the scan signal VG is applied at low potential, the pixel voltage VP1 charged to the storage capacitor is continuously supplied to the pixel electrode to maintain driving of the liquid crystal.

The variation ΔVP1 of the pixel voltage generated in the transition to the low potential of the scan signal VG will be described in more detail with reference to the accompanying drawings.

3 is a view briefly illustrating charging characteristics of a pixel.

Referring to FIG. 3, a gate line for supplying a scan signal, a data line for supplying image information, a gate electrode 10 are connected to the gate line, and a source electrode 11 is connected to the data line. A storage capacitor in which charges are charged by an electric field between the switching element TFT1 having a drain electrode 12 connected to the pixel electrode, a common electrode and a pixel electrode for driving a liquid crystal by forming a constant electric field, and the common electrode and the pixel electrode. And a liquid crystal capacitor 16.

A parasitic capacitance exists between the electrodes of the switching element TFT1. A source-drain parasitic capacitance Cds, a drain-gate parasitic capacitance Cgd, and a gate-source parasitic capacitance Cgs are respectively generated.

When a high potential scan signal is applied to the gate electrode 10 of the switching element TFT1 through the gate line, the switching element TFT1 is turned on, and image information supplied from the data line is The switching element TFT1 is applied through the source electrode 11 and is applied to the pixel electrode through the drain electrode 12 at the pixel voltage. A voltage difference is generated between the common electrode to which a constant DC voltage is applied and the pixel electrode to which the pixel voltage is applied, thereby driving the liquid crystal, and the storage capacitor Cs and the liquid crystal capacitor Clc are charged.

On the other hand, when the scan signal transitioned to the low potential through the gate line is applied to the gate electrode 10 of the switching element TFT1, the switching element TFT1 is turned off. At this time, due to the transient transition from the high potential to the low potential, the coupling phenomenon causing a signal change between the parasitic capacitance, the storage capacitor Cs, and the liquid crystal capacitor Clc between the electrodes of the switching element TFT1. This occurs, causing a voltage drop from the pixel voltage. This is expressed as the following equation.

In Equation 1, ΔVP denotes a change in pixel voltage, Vgh denotes a high potential scan signal, and Vgl denotes a low potential scan signal.

The variation ΔVP of the pixel voltage caused by the voltage drop as described above causes a poor driving of the liquid crystal display device. That is, when image information representing the same image is applied with positive and negative pixel voltages, the absolute value of the voltage difference with the common voltage must be the same. However, as voltage drops occur at the positive pixel voltage and the negative pixel voltage, respectively, the voltage difference between the positive pixel voltage and the common voltage and the voltage difference between the negative pixel voltage and the common voltage do not have the same absolute value. Therefore, a flicker phenomenon may occur in which the luminance is unevenly displayed on the same screen, and there is a charge capacity that is not completely canceled by the voltage difference when the pixel voltage transitions from positive to negative or from negative to positive. The afterimage is displayed on the screen.

Conventionally, a high-potential scan signal conversion (Vgh modulation) method is mainly used to reduce bad driving of the liquid crystal display device due to the voltage drop of the pixel voltage as described above. The high potential scanning signal conversion method will be described below with reference to the accompanying drawings.

4 is a waveform diagram illustrating a relationship between a scan signal and a pixel voltage according to a high potential scan signal conversion (Vgh modulation) method.

Referring to FIG. 4, the scan signal VG is sequentially applied to the gate lines every frame, and the common voltage VCOM is applied to a DC voltage having a constant level. Then, on the basis of the common voltage VCOM, the image information VDATA is applied in an inversion manner so as to be positive and negative.

In the turn-on period of the thin film transistor to which the scan signal VG is applied at high potential, the image information VDATA applied to the pixel electrode is charged in a storage capacitor, which is represented by the pixel voltage VP2 waveform shown. .

Before the scan signal VG transitions from the high potential to the low potential, that is, before the falling edge, the voltage level is decreased for a certain period (ΔW1) of the high potential section. It is a transition.

The voltage level reduced in the high potential section of the scan signal VG is limited to a decrease by a voltage for maintaining the turn-on state of the switching element.

As described above, by reducing the voltage level of the high potential during the high potential period of the scan signal (VG), the voltage difference between the high potential and the low potential of the scan signal in the (Vgh-Vgl) portion of Equation 1, When the falling edge of the scan signal VG is obtained, the variation ΔVP2 of the pixel voltage reduced by a certain amount can be obtained.                         

Therefore, when the scan signal VG transitions to a low potential, coupling is performed according to parasitic capacitance, storage capacitance, and liquid crystal capacitance due to over-lap of the gate electrode and the source electrode of the thin film transistor. By reducing the voltage drop from the image voltage VP2 caused by the phenomenon, it is possible to reduce the driving failure of the liquid crystal display device which appears as flicker or afterimage.

However, when the voltage level is reduced in the scan signal high potential section, a slight voltage drop may occur in the pixel voltage due to the parasitic capacitance and the coupling phenomenon. Therefore, when the scan signal transitions from the high potential to the low potential, even if the voltage drop is reduced to reduce the variation of the pixel voltage, the reduction effect of the pixel voltage variation is not large.

Accordingly, the present invention has been devised to solve the above-described problems, and an object of the present invention is to accurately compensate for the variation of the pixel voltage caused by the voltage drop occurring during the potential transition of the scan signal, thereby reducing the voltage drop of the pixel voltage. Disclosed is a driving unit of a liquid crystal display device and a driving method thereof for preventing a driving failure of a liquid crystal display device such as flicker or an afterimage phenomenon that may occur.

In order to achieve the object of the present invention, the driving unit of the liquid crystal display device selects a gray voltage corresponding to image information and outputs the pixel voltage as a pixel voltage, and compensates for the variation of the pixel voltage generated at the falling edge of the scan signal. Selectively outputs a compensation voltage, and applies the compensation voltage before the falling edge of the scan signal to be equal to the voltage level of the pixel voltage dropped and the voltage level charged in the pixel voltage before applying the compensation voltage. A voltage compensator for compensating for the variation of the pixel voltage, a first charger for charging with the gray voltage of the gray voltage part, a second charger for charging with a compensation voltage of the voltage compensator, and the gray level according to the first control signal. Electrically connecting a voltage part to the first charging part and charging the gray voltage of the gray voltage part to the first charging part A first switching unit which cuts off the power or cuts off the connection between the gray voltage unit and the first charging unit and electrically connects the first charging unit and the output to output the gray voltage charged in the first charging unit. And the output is cut off according to a second control signal and electrically connected to the voltage compensating unit and the second charging unit and charging the compensation voltage of the voltage compensating unit to the second charging unit or the voltage compensating unit and the second charging unit. And a second switching unit which cuts off the connection and outputs the compensation voltage charged in the second charging unit.
The gray voltage unit is connected in series, a plurality of resistors of the R-STRING type to form a plurality of gray voltages by sequentially dropping the power supply voltage, and a first decoder and a first to select a gray voltage based on the image information. A second decoder, a plurality of switching elements individually connected to the plurality of resistors to apply or block a gray voltage, a plurality of word lines and bit lines connected to the plurality of switching elements, and the second Selective switching elements selectively driven by the decoder.
The voltage compensator is connected in series, a plurality of resistors of the R-STRING type to form a plurality of compensation voltages by sequentially dropping the power supply voltage, and a third decoder and a third decoder for selecting a compensation voltage based on image information. A fourth decoder, switching elements individually connected to the plurality of resistors to apply or block a gray voltage, a plurality of word lines and bit lines connected to the plurality of switching elements, and the fourth Selective switching elements selectively driven by the decoder.
The word lines are electrically connected to gate electrodes of the plurality of switching devices, and the bit lines are electrically connected to drain electrodes of the plurality of switching devices.
The plurality of switching elements are driven through the word lines, and a gray voltage is selectively applied from the plurality of switching elements through the bit lines.
The plurality of switching elements are driven through the word lines, and a compensation voltage is selectively applied from the plurality of switching elements through the bit lines.
When the first control signal is at a low potential, the gray voltage of the gray voltage unit is charged to the first charging unit through the first switching unit.
When the first control signal is at high potential, the gray voltage charged in the first charging unit is output through the first switching unit.

The driving unit of the liquid crystal display of the present invention as described above will be described in detail with reference to the accompanying drawings.

5 is a block diagram illustrating a driving unit of the liquid crystal display according to the first embodiment of the present invention.

Referring to FIG. 5, a gray voltage unit 100 for selecting a gray voltage corresponding to image information and outputting the pixel voltage as a pixel voltage, and a voltage compensator 102 for compensating for variations in pixel voltage occurring at the falling edge of the scan signal. ), A first charging unit 112 for charging the gray voltage of the gray voltage unit 100, a second charging unit 122 for charging the compensation voltage of the voltage compensation unit 102, and a first control signal ( The voltage compensating unit (1) by the first switching unit (111) and the second control signal (VP_C) outputting the gray level voltage of the gray voltage unit (100) to the first charging unit (112) by SOE. And a second switching unit 121 for applying a compensation voltage of the output 102 to the second charging unit.

The gray voltage unit 100 selects a gray voltage corresponding to the applied image information and applies the gray voltage to the first switching unit 111. The first switching unit 111 electrically connects the gray voltage unit 100 and the first charging unit 112 and cuts an output when the first control signal SOE is applied at a low potential. The gray voltage selectively applied from the gray voltage unit 100 is charged in the first charging unit 112 through the first switching unit 111. In addition, when the first control signal SOE is applied at high potential, the first switching unit 111 cuts off the connection between the gradation voltage unit 100 and the first charging unit 112 and the first switching unit SOE. As the charging unit 112 and the output side are electrically connected, the gray voltage charged in the first charging unit 112 is output through the first switching unit 111.

Meanwhile, the voltage compensator 102 selectively applies a compensation voltage corresponding to the applied image information to the second switching unit 121. The second switching unit 121 is driven by the second control signal VP_C. When the second control signal VP_C has a low potential, the second switching unit 121 cuts an output and the voltage The compensation unit 102 and the second charging unit 122 are electrically connected to each other, and the compensation voltage selectively applied by the voltage compensation unit 102 may be applied to the second charging unit 122 through the second switching unit 121. ) Is charged. When the second control signal VP_C is applied at high potential, the second switching unit 121 cuts off the connection between the voltage compensating unit 102 and the second charging unit C21, and the second The compensation voltage charged in the charging unit 122 is output through the second switching unit 121.

Therefore, the gray level voltage output through the first switching unit 111 and the compensation voltage output through the second switching unit 121 are combined and output.

FIG. 6 is a block diagram of the liquid crystal display driver of FIG. 5 in an equivalent circuit.

Referring to FIG. 6, a liquid crystal display driving unit is connected in series to form a plurality of gray voltages by sequentially dropping a power supply voltage to form a plurality of gray voltages, and one gray voltage by image information. A first decoder 230 and a second decoder 231 for selecting the switching element, switching elements TFT11 connected to the plurality of resistors separately to apply or block a gray voltage, and the switching element TFT11 Gradation including a plurality of word lines and bit lines connected to the plurality of lines, and selection switching elements S11 to S14 selectively driven by the second decoder 231. A voltage unit 200; A third decoder 240 connected in series to sequentially lower the power supply voltage to form a plurality of compensation voltages, and selecting one compensation voltage based on image information; A fourth decoder 241, switching elements TFT11 that are individually connected to the plurality of resistors to apply or block a gray voltage, and a plurality of word lines that are connected to the switching elements TFT11. A voltage compensator 202 including LINEs and bit lines, and selection switching elements S21 to S24 selectively driven by the fourth decoder 241; A first charging unit C11 for charging a gradation voltage selectively applied by the gradation voltage unit 200; A second charging unit C21 for charging a compensation voltage selectively applied by the voltage compensation unit 202; A first switching unit SW11 for applying the gradation voltage selected by the gradation voltage unit 200 to the first charging unit C11 or outputting the gradation voltage from the first charging unit C11; And a second switching unit SW21 for applying the compensation voltage selected by the voltage compensating unit 202 to the second charging unit C21 or outputting it from the second charging unit C21.

The driving unit of the liquid crystal display device is illustrated when the digital image information is 4 bits. For example, the gray voltage unit 200 has a plurality of resistors connected in series, and the plurality of resistors have a folded R-STRING type. It is composed. Then, a power supply voltage is applied to one side of the R-STRING, and the voltage drops sequentially to form a plurality of gray voltages.

The first decoder 230 applies a signal by selecting one line among a plurality of word lines based on 2 bits of image information among 4 bits of image information.

A plurality of switching elements are individually connected to the plurality of resistors, a gate electrode of the switching element is connected to a word line, and a drain electrode of the switching element is connected to a bit line. A plurality of switching elements are connected to a word line of the switch line, and the switching elements are individually connected to the plurality of resistors.

The first decoder 230 applies a signal through a word line corresponding to the applied image information, and switching elements connected to the word line are turned on, and the switching element The gray voltages corresponding to the first and second gray voltages are applied to the plurality of bit lines through the drain electrode of the switching elements. The second decoder 231 selects and turns on one of the plurality of selection switching elements S11 to S14 based on 2 bit image information among 4 bit image information. BIT LINE is selectively applied to the first switching unit SW11 through the turned-on selection switching elements S11 to S14.

The first switching unit SW11 is connected to the terminal A11 of the gradation voltage unit when the first control signal, that is, the SOE signal (not shown) is at a low potential, and is applied from the gradation voltage unit 200. The selected gray voltage is charged in the first charging unit C11 through the first switching unit SW11. When the SOE signal is in a high potential state, the first switching unit SW11 is connected to an output terminal A12 so that the gray level voltage charged in the first charging unit C11 is changed to the first switching unit SW11. Is printed through).

The voltage compensator 202 has the same configuration as the gray voltage part 200.

The voltage compensator 202 is configured in a folded state in which a plurality of resistors are connected in series, and forms a plurality of compensation voltages by sequentially dropping a power supply voltage applied to one side of the series connected resistors.

Switching elements TFT11 are individually connected to the plurality of resistors to individually select the plurality of resistors.

The third decoder 240 selectively applies a signal to one word line among the plurality of word lines by the applied image information, and connects the signal to the selected word line. The switching elements TFT11 are turned on, and compensation voltages corresponding to the switching element TFT11 are applied to the bit line BIT LINE through the switching element TFT11. In addition, when the fourth decoder 241 selects one of the plurality of selection switching elements S21 to S24 and applies a signal according to the image information to be applied, the fourth switching unit 241 selects the selection switching element. In the turn-on state, a compensation voltage is selectively applied from the word line selected by the third decoder 240 through the bit line, and the compensation voltage is applied to the second switching unit. (SW21).                     

The second switching unit SW21 is electrically connected to the voltage compensating unit terminal A21 when the second control signal is at a low potential, and the voltage compensating unit 202 and the second charging unit C21 are electrically connected to each other. Since it is connected, the compensation voltage selected by the voltage compensator 202 is charged to the second charger C21 through the second switching unit SW21.

In addition, when the second control signal is in a high potential state, the second switching unit SW21 is connected to the output side terminal A22 so that the voltage compensating unit 202 and the second charging unit C21 are electrically connected. Since it is blocked by, the compensation voltage charged in the second charging unit (C21) is output through the second switching unit (SW21).

Accordingly, by adding the compensation voltage output from the voltage compensator 202 to the gray voltage output from the gray voltage unit 200, the liquid crystal display device compensates for the variation of the pixel voltage at the falling edge of the scan signal in advance. It is possible to prevent the drive failure of the.

7 is a waveform diagram illustrating an operating waveform of a driving unit of a liquid crystal display according to a first embodiment of the present invention.

Referring to FIG. 7, the scan signal VG is sequentially applied to the gate lines every frame, and the common voltage VCOM is applied to a DC voltage having a constant level. Then, on the basis of the common voltage VCOM, the image information VDATA is applied in an inversion manner so as to be positive and negative.

In the turn-on period of the thin film transistor to which the scan signal VG is applied at high potential, the image information VDATA applied to the pixel electrode is charged in a storage capacitor, which is represented by the pixel voltage VP11 waveform shown. .

Meanwhile, in the turn-off period of the thin film transistor to which the scan signal VG is applied at low potential, the pixel voltage VP11 charged in the storage capacitor is continuously supplied to the pixel electrode to maintain driving of the liquid crystal.

The image information is charged to the storage capacitor during the high potential period from the rising edge to the falling edge of the scan signal, and the pixel is coupled to the coupling phenomenon due to the parasitic capacitance of the gate electrode and the source electrode of the switching element at the falling edge of the scan signal. The voltage drop of the voltage occurs. However, in the present invention, the pixel voltage is applied before the falling edge of the scan signal by applying the compensation voltage output from the voltage compensator described in FIGS. 5 and 6 to the pixel electrode at a predetermined time T10 in the high potential section of the scan signal. Raise the voltage level. That is, by applying the compensation voltage of the variation of the pixel voltage (ΔVP11) output from the voltage compensator before the falling edge of the scanning signal, the voltage level after the voltage drop of the pixel voltage at the falling edge is charged by the original image information. Set the voltage level to

Therefore, by applying a compensation voltage according to the respective image information applied to each pixel, it is possible to have a voltage level charged by the original image information after the voltage drop, to prevent flicker or afterimage, and to prevent driving failure of the liquid crystal display device. do.

As described above, the driving unit of the liquid crystal display according to the present invention applies a compensation voltage to the high potential section of the scan signal in advance to compensate for the variation of the pixel voltage caused by the voltage drop occurring at the falling edge of the scan signal. When the voltage level of the pixel voltage dropped on the falling edge of the scanning signal is set to the charged voltage level of the pixel voltage before applying the compensation voltage, flicker or afterimage caused by the fluctuation of the pixel voltage generated on the falling edge of the scanning signal Can prevent the driving failure of the liquid crystal display device.

Claims (9)

A gray voltage unit for selecting a gray voltage corresponding to the image information and outputting the gray voltage; And selectively outputs a compensation voltage for compensating for the variation of the pixel voltage occurring at the falling edge of the scan signal, and applies the compensation voltage before the falling edge of the scan signal to reduce the voltage level of the pixel voltage and the compensation voltage. A voltage compensator for compensating for the variation of the pixel voltage so as to be equal to the voltage level charged in the pixel voltage before applying? A first charging unit which is charged by receiving the gray voltage of the gray voltage unit; A second charging unit which charges by applying a compensation voltage of the voltage compensating unit; Electrically connecting the gradation voltage unit and the first charging unit according to a first control signal, charging the gradation voltage of the gradation voltage unit to the first charging unit and blocking the output, or blocking the output of the gradation voltage unit and the first charging unit A first switching unit which cuts off a connection and electrically connects the first charging unit and the output to output the gray scale voltage charged in the first charging unit; And According to a second control signal, the output is cut off, and the voltage compensation unit and the second charging unit are electrically connected to each other and the compensation voltage of the voltage compensation unit is charged to the second charging unit or the voltage compensation unit and the second charging unit And a second switching unit which cuts off a connection and outputs the compensation voltage charged in the second charging unit. The gradation voltage unit of claim 1, wherein the gradation voltage unit is connected in series, and the gradation voltage is selected based on a plurality of resistors having an R-STRING type to form a plurality of gradation voltages by sequentially lowering the power supply voltage. A first decoder and a second decoder, switching elements individually connected to the plurality of resistors to apply or block a gray voltage, and a plurality of word lines and bit lines connected to the plurality of switching elements. And selective switching elements selectively driven by the second decoder. The voltage compensation unit of claim 1, wherein the voltage compensation unit is connected in series, and selects a compensation voltage based on a plurality of resistors having an R-STRING type for forming a plurality of compensation voltages by sequentially lowering the power supply voltage. A third decoder and a fourth decoder, switching elements individually connected to the plurality of resistors to apply or block a gray voltage, and a plurality of word lines and bit lines connected to the plurality of switching elements. And selective switching elements selectively driven by the fourth decoder. The liquid crystal of claim 2 or 3, wherein the word lines are electrically connected to gate electrodes of the plurality of switching elements, and the bit lines are electrically connected to drain electrodes of the plurality of switching elements. Drive part of display device. 3. The driving unit of claim 2, wherein the plurality of switching elements are driven through the word lines, and a gray level voltage is selectively applied from the plurality of switching elements through the bit lines. 4. The driving unit of claim 3, wherein the plurality of switching elements are driven through the word lines, and a compensation voltage is selectively applied from the plurality of switching elements through the bit lines. delete The driving unit of claim 1, wherein the gray voltage of the gray voltage unit is charged to the first charging unit through the first switching unit when the first control signal is at a low potential. 2. The driving unit of claim 1, wherein the gray level voltage charged in the first charging unit is output through the first switching unit when the first control signal is at high potential.

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