Liquid crystal display apparatus with residual image eliminating function

• US 6,317,109 B1
• Filed: 05/15/1998
• Issued: 11/13/2001
• Est. Priority Date: 05/17/1997
• Status: Expired due to Term

• Current Assignee: LG Display Co., Ltd.
• Original Assignee: LG Electronics, Inc. (LG Corporation)
• Inventors: Lee, Hyun Chang
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): Laneau, Ronald
• Application Number:
  US09/078,523
• Time in Patent Office: 1,278 Days
• Field of Search: 345/87, 345/96, 345/92, 349/42, 349/43
• US Class Current: 345/87
• CPC Class Codes: G09G 2320/0204 Compensation of DC component across the pixels in flat panels
• CPC Class Codes: G09G 2320/0219 Reducing feedthrough effects in active matrix panels, i.e. voltage changes on the scan electrode influencing the pixel voltage due to capacitive coupling
• CPC Class Codes: G09G 2320/103 Detection of image changes, e.g. determination of an index representative of the image change
• CPC Class Codes: G09G 2330/04 Display protection
• 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 3/3655 Details of drivers for counter electrodes, e.g. common electrodes for pixel capacitors or supplementary storage capacitors

Abstract

A liquid crystal display apparatus with a residual image eliminating function which can display a fine picture without a residual image on a liquid crystal display panel. The liquid crystal display apparatus compares image signals from an input line in the frame unit using a still picture detector and detect if a still picture has been displayed on the liquid crystal display panel for more than a certain time. An output signal of this still picture detector allows a data compensating means to selectively compensate an image signal in the frame unit to be supplied to the liquid crystal display panel. A direct-current voltage component accumulated in the liquid crystal cells included in the liquid crystal display panel is eliminated by the compensated image signal so that a, residual image can not appear on the liquid crystal display panel.

Claims

1. A liquid crystal display apparatus for use with a liquid crystal display panel made up of liquid crystal cells, having a function of eliminating a residual image, comprising:

means for receiving image signals on an input line;

means for determining a compensation voltage corresponding to a direct-current voltage amount accumulated in a liquid crystal cell;

a still picture detector for comparing the image signals and for outputting a predetermined signal if a picture has been displayed on the liquid crystal display panel for a predetermined time; and

a data compensator for compensating the image signals with the compensation voltage in response to the predetermined signal from the still picture detector.

2. The liquid crystal display apparatus of claim 1 wherein the still picture detector compares a current frame image signal from said input line with a previous frame image signal, increments a number whenever the current frame image signal is identical to a previous frame image signal, and outputs the predetermined signal when the number reaches a predetermined value.

3. A liquid crystal display apparatus for use with a liquid crystal display panel made up of liquid crystal cells, having a function of eliminating a residual image, comprising:

means for receiving image signals on an input line;

means for determining a compensation voltage corresponding to a direct-current voltage amount accumulated in a liquid crystal cell over a period of time spanning two or more frames;

a data compensator for compensating the image signals with the compensation voltage after the period of time; and

a common voltage generator for varying a common voltage to compensate for the accumulated direct-current voltage.

4. The liquid crystal display apparatus of claim 3 wherein the data compensator compensates the image signal periodically.

5. The liquid crystal display apparatus of claim 3 wherein the common voltage generator varies the common voltage to compensate for the accumulated direct-current voltage periodically.

6. The liquid crystal display apparatus of claim 3 further including:

a still picture detector for comparing the image signals and for outputting a predetermined signal if a picture has been displayed on the liquid crystal display panel for a predetermined time, wherein the data compensator compensates the image signal in response to the predetermined signal from the still picture detector.

7. The liquid crystal display apparatus of claim 6 wherein the common voltage generator varies the common voltage in response to the predetermined signal.

8. The liquid crystal display apparatus of claim 6 wherein the still picture detector compares a current frame image signal from said input line with a previous frame image signal, increments a number whenever the current frame image signal is identical to a previous frame image signal, and outputs the predetermined signal when the number reaches a predetermined value.

9. The liquid crystal display apparatus of claim 3 wherein the common voltage generator sets the common voltage to an intermediate value between the peak values of the common voltage to compensate for the accumulated direct-current voltage.

10. In a liquid crystal display apparatus for displaying a picture on a liquid crystal display panel that switches liquid crystal cells therein using thin film transistors, a method of eliminating a residual image comprising the steps of:

receiving image signals on an input line;

determining a compensation voltage corresponding to a direct-current voltage amount accumulated in a liquid crystal cell;

comparing the image signals and outputting a predetermined signal if a picture has been displayed on the liquid crystal display panel for a predetermined time; and

compensating the image signals with the compensation voltage in response to the predetermined signal.

11. The method of claim 10, wherein the comparing and outputting step includes the steps of:

comparing a current frame image signal from said input line with a previous frame image signal;

incrementing a number whenever the current frame image signal is identical to a previous frame image signal; and

outputting the predetermined signal when the number reaches a predetermined value.

12. In a liquid crystal display apparatus for displaying a picture on a liquid crystal display panel that switches liquid crystal cells therein using thin film transistors, a method of eliminating a residual image comprising the steps of:

receiving image signals on an input line;

determining a compensation voltage corresponding to a direct-current voltage amount accumulated in a liquid crystal cell over a period of time spanning two or more frames;

compensating the image signals with the compensation voltage after the period of time; and

varying a common voltage to compensate for the accumulated direct-current voltage.

13. The method of claim 12 wherein the compensating step includes the step of:

compensating the image signal periodically.

14. The method of claim 12 wherein the varying step includes the step of:

varying the common voltage to compensate for the accumulated direct-current voltage periodically.

15. The method of claim 12 further including the steps of:

comparing the image signals and outputting a predetermined signal if a picture has been displayed on the liquid crystal display panel for a predetermined time; and

compensating the image signal in response to the predetermined signal.

16. The method of claim 15, wherein the comparing and outputting step includes the steps of:

comparing a current frame image signal from said input line with a previous frame image signal;

incrementing a number whenever the current frame image signal is identical to a previous frame image signal; and

outputting the predetermined signal when the number reaches a predetermined value.

17. The method of claim 15 wherein the varying steps includes the step of:

varying the common voltage in response to the predetermined signal.

18. The method of claim 12 wherein the varying step includes the step of:

varying the common voltage to an intermediate value between the peak values of the common voltage to compensate for the accumulated direct-current voltage.