KR101323469B1 - Driving liquid crystal display and apparatus for driving the same - Google Patents

Abstract

The present invention relates to a liquid crystal display device and a driving method thereof to improve the display quality of a liquid crystal display device driven by a 2-dot inversion method.

The liquid crystal display includes: a liquid crystal panel in which data lines supplied with analog data voltages and gate lines supplied with scan signals are crossed and liquid crystal cells are arranged in a matrix; A control signal generation circuit for generating a polarity control signal for instructing polarity inversion of the data voltage in units of N (N is a positive integer of two or more) horizontal periods and for generating a compensation polarity control signal having a period shorter than the polarity control signal; And a data driving circuit which modulates a value of digital video data in response to the compensation polarity control signal, converts the modulated digital video data into the analog data voltage, and supplies the modulated digital video data to the data lines.

Description

Liquid crystal display and its driving method {DRIVING LIQUID CRYSTAL DISPLAY AND APPARATUS FOR DRIVING THE SAME}

1 is a diagram schematically showing data polarity of a liquid crystal panel driven in a 1-dot-version system.

FIG. 2 is a diagram schematically illustrating data polarity of a liquid crystal panel driven in a two dot inversion scheme. FIG.

3 is a waveform diagram showing a polarity control signal and a data voltage generated in a one dot inversion scheme.

4 is a waveform diagram showing a polarity control signal and a data voltage generated in a 2-dot inversion scheme.

5 is a block diagram schematically illustrating a liquid crystal display device driven in a two dot inversion scheme.

6 is an enlarged view illustrating a 4 × 4 liquid crystal cell matrix in the liquid crystal panel of FIGS. 3 and 8.

FIG. 7 is a waveform diagram illustrating a data voltage and a scan pulse of a 2-dot inversion method charged in a liquid crystal cell matrix as shown in FIG. 6.

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

9 is a waveform diagram illustrating a polarity control signal, a compensation polarity control signal, and a data voltage shown in FIG. 8;

FIG. 10 is a circuit diagram showing in detail the data driving circuit shown in FIG. 8; FIG.

Description of the Related Art

41, 81: timing controller 42, 82: data drive circuit

43, 83: gate driving circuit 44, 84: liquid crystal panel

101: shift register 102: latch

103: subtractor 104: digital-to-analog converter

105: output circuit 106: register

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 for improving display quality of a liquid crystal display device driven by a 2-dot inversion method.

The liquid crystal display displays an image by adjusting the light transmittance of the liquid crystal cells according to a video signal. In an active matrix liquid crystal display device, switching elements are formed for each liquid crystal cell, which is advantageous for displaying a moving image. A thin film transistor (hereinafter referred to as "TFT") is mainly used as a switching element.

The LCD is driven in an inversion manner to reduce flicker and afterimage by periodically inverting the polarity of data charged in the liquid crystal cell. The inversion method includes a line inversion method of inverting the polarity of data between adjacent liquid crystal cells in the vertical line direction, a version method of inverting the polarity of data between adjacent liquid crystal cells in the horizontal line direction, a vertical line direction and a horizontal line direction There is a dot inversion method in which the polarity of data between adjacent liquid crystal cells is reversed. Among these inversion methods, the dot inversion method shows little flicker in the vertical and horizontal directions.

1, the polarity of data supplied to adjacent liquid crystal cells in the vertical direction is opposite to the polarity of data supplied to adjacent liquid crystal cells in the horizontal direction. The polarity of the data is inverted every frame (Fn-1, Fn). This one-dot inversion method is most commonly used in liquid crystal display devices because flicker is small in both the vertical and horizontal directions.

In the two-dot inversion scheme, as shown in FIG. 2, the polarity of the data is inverted by two dots in the vertical direction, that is, two liquid crystal cells. The two-dot inversion method has lower power consumption and relatively smaller flicker in both the vertical and horizontal directions than the one-dot inversion method as shown in FIG.

3 shows an example of the data voltage and the polarity control signal POL1 in the one dot inversion scheme. 4 shows an example of the data voltage and the polarity control signal POL2 in the 2-dot inversion scheme.

3 and 4, the polarity control signals POL1 and POL2 select the positive data voltage and the negative data voltage output from the digital-analog converter in the data drive integrated circuit. Therefore, the polarity of the data voltage is determined by the polarity control signals POL1 and POL2. The polarity control signal POL1 of the one dot inversion scheme as shown in FIG. 3 is inverted in the unit of one horizontal period 1H and inverted in every horizontal period of the polarity of the data voltage supplied to the data lines. The polarity control signal POL2 of the two-dot inversion method as shown in FIG. 4 inverts polarity in units of two horizontal periods 2H and inverts every two horizontal periods of polarity of data voltages supplied to the data lines.

5 schematically illustrates a conventional liquid crystal display device driven in a two dot inversion method. FIG. 6 is an equivalent circuit diagram of a lower array substrate of a 4 × 4 liquid crystal cell matrix of the liquid crystal panel illustrated in FIG. 5.

Referring to FIGS. 5 and 6, the liquid crystal display according to the related art has a liquid crystal in which data lines D1 to Dm and gate lines G1 to Gn intersect and TFTs for driving the liquid crystal cell Clc are formed at the intersections thereof. Scan pulses are applied to the panel 44, the data driver circuit 42 for supplying data to the data lines D1 to Dm of the liquid crystal panel 44, and the gate lines G1 to Gn of the liquid crystal panel 44. A gate driving circuit 43 for supplying, and a timing controller 41 for controlling the data driving circuit 42 and the gate driving circuit 43 are provided.

The data driving circuit 42 inverts the polarity of the data voltage supplied to the data lines D1 to Dm in units of two horizontal periods in response to the polarity control signal POL2 supplied from the timing controller 41. The voltage is supplied to the data lines D1 to Dm.

The gate driving circuit 43 sequentially supplies scan pulses to the gate lines G1 to Gn under the control of the timing controller 41.

The timing controller 41 controls the gate control signal GDC and the data driving circuit 42 for controlling the gate driving circuit 43 by using the vertical / horizontal synchronization signals V and H and the clock CLK. To generate a data control signal DDC. The data control signal DDC includes a source start pulse SSP, a source shift clock SSC, a source output enable signal SOE, a polarity control signal POL2, and the like. The gate control signal GDC includes a gate shift clock GSC, a gate output enable GOE, a gate start pulse GSP, and the like.

FIG. 7 illustrates polarities and scan pulses of the data voltages supplied to the first to fourth liquid crystal cells A to D arranged in the first column in the 4 × 4 liquid crystal cell matrix shown in FIG. 6. In FIG. 7, reference numerals GP1 to GP4 denote scan pulses applied to the gate lines G1 to G4.

6 and 7, the liquid crystal display of the two dot inversion method inverts the polarity of the data voltage every two horizontal periods. Therefore, among the liquid crystal cells A to D of the first column supplied with data by the first data line DL1, the liquid crystal cell A of the first horizontal line and the liquid crystal cell B of the second horizontal line are common. While a positive data voltage higher than the voltage Vcom is applied, the liquid crystal cell C of the third horizontal line HL3 and the liquid crystal cell D of the fourth horizontal line HL4 are less than the common voltage Vcom. A low negative data voltage is applied.

However, in the two-dot inversion method, the amount of charge of the data charged in the liquid crystal cell to which the positive data voltage rising from the negative data voltage is applied and the liquid crystal cell to which the other positive data voltage is supplied subsequent to the positive data voltage are different. . In addition, in the two-dot inversion method, the amount of charge of data charged in a liquid crystal cell to which a negative data voltage descending from the positive data voltage is applied is different from a liquid crystal cell to which another negative data voltage is applied subsequent to the negative data voltage. do.

This means that the rising time of changing from the negative data voltage to the positive data voltage of the opposite polarity or the falling time of changing from the positive data voltage to the negative data voltage of the opposite polarity is very long. . On the contrary, the rising time of changing from the positive data voltage to the positive data voltage of such polarity or the falling time of changing from the negative data voltage to the negative data voltage of such polarity is relatively small.

Due to such a difference in charging characteristics, even when the data voltage of the same gray level is compared with the liquid crystal cells A and C of the first and third horizontal lines HL1 and HL3 in the normally white mode, The liquid crystal cells B and D of the second and fourth horizontal lines HL2 and HL4 appear brighter, and the liquid crystals of the first and third horizontal lines HL1 and HL3 are displayed in the normally white mode. Compared to the cells A and C, the liquid crystal cells B and D of the second and fourth horizontal lines HL2 and HL4 appear darker. As a result, in the two-dot inversion method, the luminance difference between the horizontal lines is generated according to whether or not the polarity of the previously generated data voltage and the subsequent data voltage is changed.

Accordingly, an object of the present invention is to provide a liquid crystal display device and a driving method thereof to improve the display quality of a liquid crystal display device driven by a 2-dot inversion method.

In order to achieve the above object, a liquid crystal display according to an exemplary embodiment of the present invention includes a liquid crystal panel in which data lines supplied with analog data voltages and gate lines supplied with scan signals are crossed and liquid crystal cells are arranged in a matrix form; A control signal generation circuit for generating a polarity control signal for instructing polarity inversion of the data voltage in units of N (N is a positive integer of two or more) horizontal periods and for generating a compensation polarity control signal having a period shorter than the polarity control signal; And a data driving circuit which modulates a value of digital video data in response to the compensation polarity control signal, converts the modulated digital video data into the analog data voltage, and supplies the modulated digital video data to the data lines.

The data driver circuit may include a shift register configured to sequentially generate a sampling signal; A latch for sequentially latching and simultaneously outputting the digital video data; A subtractor for subtracting the digital video data input from the latch by a predetermined compensation value; A digital-to-analog converter for converting the digital video data subtracted by the subtractor into the analog data voltage; And an output circuit for selecting the polarity of the analog data voltage from the digital-analog converter in response to the polarity control signal and supplying the polarity to the data lines.

The logic control signal is inverted in a logic value in units of two horizontal periods, and the compensation polarity control signal is inverted in a logic value in units of one horizontal period.

The logic value of the compensation polarity control signal is inverted when the logic value of the polarity control signal is inverted and inverted within a period in which the logic value of the polarity control signal is maintained.

A method of driving a liquid crystal display according to an exemplary embodiment of the present invention includes generating a polarity control signal instructing polarity inversion of a data voltage in units of N (N is a positive integer of 2 or more) horizontal period; Generating a compensation polarity control signal having a shorter period than the polarity control signal; Performing modulation to lower the value of the digital video data in response to the compensation polarity control signal; And converting the modulated digital video data into the analog data voltage and supplying the modulated digital video data to data lines of a liquid crystal panel.

Other objects and advantages of the present invention in addition to the above object will become apparent from the description of the preferred embodiment of the present invention with reference to the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 8 to 10.

8 and 9, the liquid crystal display according to the exemplary embodiment of the present invention converts the value of the digital video data in response to the compensation polarity control signal POL_comp and in response to the two-dot polarity control signal POL2. A data driving circuit 82 for converting polarities of analog data voltages to be supplied to the liquid crystal panel 84 and a gate driving circuit 83 for supplying scan pulses to the gate lines G1 to Gn of the liquid crystal panel 84. And a timing controller 81 for controlling the data driving circuit 82 and the gate driving circuit 83.

The liquid crystal panel 84 is a liquid crystal is injected between the two glass substrates, the data lines (D1 to Dm) and the gate lines (G1 to Gn) are formed on the lower glass substrate to be perpendicular to each other. The TFTs formed at the intersections of the data lines D1 to Dm and the gate lines G1 to Gn liquid crystal the data on the data lines D1 to Dm in response to a scan pulse from the gate lines G1 to Gn. It is supplied to the cell Clc. To this end, the gate electrode of the TFT is connected to the gate lines G1 to Gn, and the source electrode thereof is connected to the data lines D1 to Dm. The drain electrode of the TFT is connected to the pixel electrode of the liquid crystal cell Clc. A common voltage (Vcom) is supplied to the common electrode facing the pixel electrode. Reference numeral 'Cst' denotes a storage capacitor. The storage capacitor Cst may be formed between the liquid crystal cell Clc connected to the k-th gate line (where k is a positive integer between 1 and n) and the k-1 th front gate line.

The data driving circuit 82 transmits the digital data RGB input from the timing controller 81 to the data lines D1 to Dm with the same polarity in response to the compensation polarity control signal POL_comp from the timing controller 81. The charging property of the second data is compensated for by comparing the first data by subtracting a preset compensation value to the digital video data corresponding to the second of the two data to be supplied continuously. One period of the compensation polarity control signal POL_comp corresponds to two horizontal periods 2H as shown in FIG. 9, and its pulse width corresponds to one horizontal period 1H. The period of the 2-dot polarity control signal POL corresponds to 4 horizontal periods as shown in FIG. 9, and the pulse width corresponds to 2 horizontal periods 2H.

The data driving circuit 82 converts the digital video data into an analog gamma compensation voltage to generate analog data voltages to be supplied to the data lines D1 to Dn, and the 2-dot polarity control signal from the timing controller 81 In response to POL), the polarities of the analog data voltages are inverted in units of two horizontal periods. A detailed description of the data driving circuit 82 will be described in detail with reference to FIG. 10.

The gate driving circuit 83 sequentially supplies scan pulses to the gate lines G1 to Gn in response to the control signal GDC from the timing controller 81.

The timing controller 81 controls the gate control signal GDC and the data driving circuit 82 to control the gate driving circuit 83 by using the vertical / horizontal synchronization signals V and H and the clock CLK. Generates a data control signal DDC (POL2) and a compensation polarity control signal POL_comp. The data control signal DDC POL2 includes a source start pulse SSP, a source shift clock SSC, a source output signal SOE, a polarity control signal POL, and the like. The gate control signal GDC includes a gate shift clock GSC, a gate output signal GOE, a gate start pulse GSP, and the like.

6 and 9, the two-dot inversion driving of the liquid crystal display according to the present invention will be described as follows.

6 and 9, the two-dot inversion driving method according to the present invention includes a two-dot polarity control signal POL2 and a two-dot polarity control signal POL whose polarities are inverted in units of two horizontal periods (2H). A compensation polarity control signal POL_comp is generated which is inverted to a low potential at each of the rising edge and the falling edge of and is inverted to a high potential at a half time point of the pulse width period of the 2-dot polarity control signal POL.

In the two-dot inversion method, positive data is included in the liquid crystal cell A of the first horizontal line HL1 and the liquid crystal cell B of the second horizontal line HL2 among the liquid crystal cells A to D in the first column. Voltage is supplied. At this time, the two-dot polarity control signal POL2 maintains a high voltage, and the compensation polarity control signal POL_comp is low during the period in which the liquid crystal cell A of the first horizontal line HL1 maintains the positive polarity data voltage. After the voltage is maintained, at the time when the positive data voltage is supplied to the liquid crystal cell B of the second horizontal line HL2, the voltage is inverted to a high voltage and the high voltage is maintained for one horizontal period 1H. When the compensation polarity control signal POL_comp changes to a high voltage, the value of the digital video data RGB is the positive data voltage (or absolute value) charged in the liquid crystal cell B of the second horizontal line HL2 at the same gray level. Voltage is reduced by a predetermined compensation value. That is, according to the present invention, the value of the digital video data RGB corresponding to the positive data voltage to be charged in the liquid crystal cell B of the second horizontal line HL2 is modulated lower and thus the positive data voltage lower than the original voltage. The liquid crystal cell B can be charged.

A negative data voltage is supplied to the liquid crystal cell C of the third horizontal line HL3 and the liquid crystal cell D of the fourth horizontal line HL4 among the liquid crystal cells A to D in the first column. At this time, the two-dot polarity control signal POL2 maintains a low voltage, and the compensation polarity control signal POL_comp is provided during the period in which the liquid crystal cell C of the third horizontal line HL3 maintains the negative data voltage. After the low voltage is maintained, the voltage is inverted to a high voltage at the time when the negative data voltage starts to be supplied to the liquid crystal cell D of the fourth horizontal line HL4, and the high voltage is maintained for one horizontal period 1H. At the time when the compensation polarity control signal POL_comp changes to a high voltage, the value of the digital video data RGB increases the negative data voltage charged in the liquid crystal cell D of the fourth horizontal line HL4 at the same gray level. It is reduced by a preset compensation value (or to lower the absolute value of the negative data voltage). That is, according to the present invention, the value of the digital video data RGB corresponding to the negative data voltage to be charged in the liquid crystal cell D of the fourth horizontal line HL4 is modulated lower and thus higher than the original voltage. The liquid crystal cell B can be charged.

For example, in the two-dot inversion driving method according to the embodiment of the present invention, as shown in FIG. 10, the digital video data RGB is 6 bits, the gradation value is "31", and the compensation value is experimentally determined as "1". Then, the tone value of the original digital video data RGB is modulated to " 30 " to 011111 (RGB) -000001 (compensation value). The analog positive or negative data voltage supplied to the data lines D1 to Dn by the low modulated digital video data RGB is gamma corresponding to the gray scale value "30" lower than the original gray scale value "31". Convert to compensation voltage.

By the modulation of the digital video data, the liquid crystal display according to the exemplary embodiment of the present invention applies liquid crystal cells of the first and third horizontal lines HL1 and HL3 in the normally black mode when the 2-dot inversion driving method is applied. Compared to (A, C), it is possible to prevent the liquid crystal cells B and D of the second and fourth horizontal lines HL2 and HL4 from appearing brighter, and the first and third horizontal lines in the normally white mode. Compared to the liquid crystal cells A and C of the lines HL1 and HL3, the phenomenon in which the liquid crystal cells B and D of the second and fourth horizontal lines HL2 and HL4 appear darker can be prevented.

10 schematically shows the data driving circuit 82.

Referring to FIG. 10, the data driving circuit 82 includes a plurality of data integrated circuits, each of which register 106 receives digital video data RGB from the timing controller 81. ), A shift register 101 which sequentially generates a sampling signal, a latch 102, a subtractor 103, and a digital-to-analog converter (Digital to analog), which are connected in a cascade between the register 106 and the data lines D1 to Dm. Analog Convertor (hereinafter referred to as "DAC") 104, and an output circuit 105 are provided.

The register 106 temporarily stores the digital video data RGB from the timing controller 81 and supplies the digital video data RGB to the latch 102.

The shift register 101 shifts the source start pulse SSP from the timing controller 81 in accordance with the source shift clock signal SSC to generate a sampling signal. In addition, the shift register 101 shifts the source start pulse SSP and transfers the carry signal to the next stage integrated circuit.

The latch 102 sequentially samples and latches the digital video data RGB according to the sampling signal input from the shift register 101, and then simultaneously supplies the latched digital video data RGB to the subtractor 103. .

The subtractor 103 subtracts the compensation value C previously stored in the digital video data RGB input from the latch 102 in response to the compensation polarity control signal POL_comp, and subtracts the subtracted digital video data RGB from the DAC. Supply to 94.

According to the present invention, the data voltages of the 2-dot inversion method are applied to the liquid crystal panel 84, and the charging characteristics are measured for each gray level. The compensation value C is determined by experimentally obtaining a subtraction value in which the charging characteristic is equal to the charging characteristic of the first data. Here, the compensation value C may be optimized for each gray level or for each gray level region including a plurality of gray levels and may be stored in the memory means in the subtractor 103 or in the memory in the timing controller 81.

The DAC 104 converts the digital video data RGB modulated by the subtractor 103 into a positive analog gamma compensation voltage GCV and a negative analog gamma voltage GCV.

The output circuit 105 is connected to each of the data lines D1 to Dm to output an output buffer for reducing the loss of data voltages supplied to the data lines D1 to Dm, a positive data voltage and a negative data voltage. It includes a multiplexer for selection. The multiplexer of the output circuit 105 selects the positive data voltage or the negative data voltage in response to the polarity control signal POL2 from the timing controller 81, and selects the data voltages of different polarities in units of two horizontal periods. The selected positive data voltage or negative data voltage is supplied to the data lines D1 to Dm.

As described above, the liquid crystal display device and the driving method thereof according to the present invention, when driving the liquid crystal panel in a two-dot inversion method, the second data having a larger charging characteristics than the first data of the two data of the same polarity By subtracting the digital value corresponding to to prevent the fringes that can occur due to the difference in the charging characteristics. As a result, the liquid crystal display device according to the present invention can display an image with high quality in which streaks do not appear when driven in the 2-dot inversion method.

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. For example, although the embodiment of the present invention has been described based on the dot inversion method, N (where N is a positive integer of 2 or more) may also be applied to the dot inversion method. In addition, embodiments disclosed in the detailed description of the invention may be used in combination. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims.

Claims (7)

A liquid crystal panel in which data lines supplied with an analog data voltage and gate lines supplied with scan signals are crossed and liquid crystal cells are arranged in a matrix; A control signal generation circuit for generating a polarity control signal for instructing polarity inversion of the data voltage in units of N (N is a positive integer of two or more) horizontal periods and for generating a compensation polarity control signal having a period shorter than the polarity control signal; And A data driving circuit which modulates a value of digital video data in response to the compensation polarity control signal, converts the modulated digital video data into the analog data voltage, and supplies the converted data to the data lines; The polarity control signal is inverted by a logic value in units of two horizontal periods, And the logic value of the compensation polarity control signal is inverted in units of one horizontal period. The method of claim 1, The data driving circuit, A shift register for sequentially generating sampling signals; A latch for sequentially latching and simultaneously outputting the digital video data; A subtractor for subtracting the digital video data input from the latch by a predetermined compensation value; A digital-to-analog converter for converting the digital video data subtracted by the subtractor into the analog data voltage; And And an output circuit for selecting the polarity of the analog data voltage from the digital-analog converter in response to the polarity control signal and supplying the polarity to the data lines. delete The method of claim 1, And the logic value of the compensation polarity control signal is inverted when the logic value of the polarity control signal is inverted and inverted within a period in which the logic value of the polarity control signal is maintained. A liquid crystal display comprising a liquid crystal panel in which data lines supplied with an analog data voltage and gate lines provided with scan signals are crossed and liquid crystal cells are arranged in a matrix form. Generating a polarity control signal instructing polarity inversion of the data voltage in units of N (N is a positive integer of 2 or more) horizontal period; Generating a compensation polarity control signal having a shorter period than the polarity control signal; Performing modulation to lower the value of the digital video data in response to the compensation polarity control signal; Converting the modulated digital video data into the analog data voltage and supplying the modulated digital video data to data lines of the liquid crystal panel; The polarity control signal is inverted by a logic value in units of two horizontal periods, And the logic value of the compensation polarity control signal is inverted in units of one horizontal period. delete 6. The method of claim 5, And the logic value of the compensation polarity control signal is inverted when the logic value of the polarity control signal is inverted and inverted within a period in which the logic value of the polarity control signal is maintained.

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