LIQUID CRYSTAL DISPLAY AND METHOD OF DRIVING THE SAME

• US 20090251451A1
• Filed: 10/09/2008
• Published: 10/08/2009
• Est. Priority Date: 04/08/2008
• Status: Active Grant

• Current Assignee: LG Display Co., Ltd.
• Original Assignee: LG Display Co., Ltd.
• Inventors: Cha, Donghoon, Jang, Suhyuk, Lee, Hwanjoo
• Granted Patent: US 8,232,950 B2
• Time in Patent Office: Days
• US Class Current: 345/211
• CPC Class Codes: G09G 2310/027 Details of drivers for data electrodes, the drivers handling digital grey scale data, e.g. use of D/A converters
• CPC Class Codes: G09G 2320/0204 Compensation of DC component across the pixels in flat panels
• CPC Class Codes: G09G 2320/0242 Compensation of deficiencies in the appearance of colours
• CPC Class Codes: G09G 2320/0276 for the purpose of adaptation to the characteristics of a display device, i.e. gamma correction
• CPC Class Codes: G09G 3/2092 Details of a display terminals using a flat panel, the details relating to the control arrangement of the display terminal and to the interfaces thereto suitable for both CRT and flat panel G09G5/003; specific for a CRT G09G1/165
• CPC Class Codes: G09G 3/3614 Control of polarity reversal in general
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence
• CPC Class Codes: G09G 3/3688 suitable for active matrices only

Abstract

A liquid crystal display and a method of driving the same are disclosed. The liquid crystal display includes a liquid crystal display panel including data lines and gate lines crossing each other, and liquid crystal cells arranged in a matrix forma, a horizontal polarity controller that compares digital video data with a critical value and inverts a logic state of a horizontal polarity conversion signal when polarities of the digital video data lean based on the comparative result, a data drive circuit that converts the digital video data into positive and negative data voltages and controls horizontal polarity inversion periods of the data voltages in response to the horizontal polarity conversion signal, and a gate drive circuit that supplies scan signals to the gate lines.

Claims

1. A liquid crystal display comprising:

a liquid crystal display panel including data lines and gate lines crossing each other, and liquid crystal cells arranged in a matrix format;

a horizontal polarity controller that compares digital video data with a critical value and inverts a logic state of a horizontal polarity conversion signal when polarities of the digital video data lean based on the comparative result;

a data drive circuit that converts the digital video data into positive and negative data voltages and controls horizontal polarity inversion periods of the data voltages in response to the horizontal polarity conversion signal; and

a gate drive circuit that supplies scan signals to the gate lines.

2. The liquid crystal display of claim 1, wherein the horizontal polarity conversion signal whose logic state is inverted controls the data drive circuit to control the horizontal polarity inversion periods of the data voltages during a next frame period.

3. The liquid crystal display of claim 1, wherein the critical value includes:

a first critical value that is compared with the digital video data;

a second critical value that is compared with a difference between the number of data to be displayed as a positive data voltage and the number of data to be displayed as a negative data voltages among the digital video data equal to or larger than the first critical value; and

a third critical value that is compared with the total number of unbalanced lines, in which the difference is equal to or larger than the second critical value, during one frame period, the unbalanced line being a line in which polarities of the data lean to any one polarity.

4. The liquid crystal display of claim 3, wherein the horizontal polarity controller includes:

a polarity counter that extracts the digital video data equal to or larger than the first critical value from the digital video data, counts the number of positive data and the number of negative data among the extracted data, and outputs a positive polarity data count and a negative polarity data count;

an unbalanced line counter that calculates a difference between the positive polarity data count and the negative polarity data count in each horizontal line of the liquid crystal display panel, counts the horizontal line, in which the difference is equal to or larger than the second critical value, as the unbalanced line, and outputs an unbalanced line count;

an unbalanced line count deciding unit that when the unbalanced line count during one frame period is equal to or larger than the third critical value, generates a control signal for differently controlling horizontal polarity inversion periods of data to be displayed on the liquid crystal display panel; and

a horizontal polarity conversion signal generating unit that inverts a logic state of the horizontal polarity conversion signal in response to the control signal.

5. The liquid crystal display of claim 1, wherein the data drive circuit lengthens horizontal polarity inversion periods of data voltages to be supplied to the data lines of the liquid crystal display panel during a next frame period in response to the horizontal polarity conversion signal.

6. The liquid crystal display of claim 5, wherein the data drive circuit lengthens the horizontal polarity inversion periods of the data voltages to be supplied to the data lines during the next frame period from a horizontal 1 dot inversion scheme to a horizontal 2 dot inversion scheme in response to the horizontal polarity conversion signal.

7. The liquid crystal display of claim 1, wherein the data drive circuit shortens horizontal polarity inversion periods of data voltages to be supplied to the data lines of the liquid crystal display panel during a next frame period in response to the horizontal polarity conversion signal.

8. The liquid crystal display of claim 7, wherein the data drive circuit shortens the horizontal polarity inversion periods of the data voltages to be supplied to the data lines during the next frame period from a horizontal 2 dot inversion scheme to a horizontal 1 dot inversion scheme in response to the horizontal polarity conversion signal.

9. A method of driving a liquid crystal display including a liquid crystal display panel including data lines and gate lines crossing each other and liquid crystal cells arranged in a matrix format, the method comprising:

comparing digital video data with a critical value and inverting a logic state of a horizontal polarity conversion signal when polarities of the digital video data lean based on the comparative result;

converting the digital video data into positive and negative data voltages and controlling horizontal polarity inversion periods of the data voltages in response to the horizontal polarity conversion signal; and

supplying scan signals to the gate lines.

10. The method of claim 9, wherein the horizontal polarity conversion signal whose the logic state is inverted controls the horizontal polarity inversion periods of the data voltages during a next frame period.

11. The method of claim 9, wherein the critical value includes:

a first critical value that is compared with the digital video data;

a second critical value that is compared with a difference between the number of data to be displayed as a positive data voltage and the number of data to be displayed as a negative data voltages among the digital video data equal to or larger than the first critical value; and

a third critical value that is compared with the total number of unbalanced lines, in which the difference is equal to or larger than the second critical value, during one frame period, the unbalanced line being a line in which polarities of the data lean to any one polarity.

12. The method of claim 11, wherein inverting the logic state of the horizontal polarity conversion signal includes:

extracting the digital video data equal to or larger than the first critical value from the digital video data, counting the number of positive data and the number of negative data among the extracted data, and outputting a positive polarity data count and a negative polarity data count;

calculating a difference between the positive polarity data count and the negative polarity data count in each horizontal line of the liquid crystal display panel, counting the horizontal line, in which the difference is equal to or larger than the second critical value, as the unbalanced line, and outputting an unbalanced line count;

generating a control signal for differently controlling horizontal polarity inversion periods of data to be displayed on the liquid crystal display panel when the unbalanced line count during one frame period is equal to or larger than the third critical value; and

inverting a logic state of the horizontal polarity conversion signal in response to the control signal.

13. The method of claim 9, wherein controlling the horizontal polarity inversion periods of the data voltages includes lengthening horizontal polarity inversion periods of data voltages to be supplied to the data lines of the liquid crystal display panel during a next frame period in response to the horizontal polarity conversion signal.

14. The method of claim 9, wherein controlling the horizontal polarity inversion periods of the data voltages includes shortening horizontal polarity inversion periods of data voltages to be supplied to the data lines of the liquid crystal display panel during a next frame period in response to the horizontal polarity conversion signal.