Liquid crystal display and method of driving the same

• US 9,202,419 B2
• Filed: 05/11/2010
• Issued: 12/01/2015
• Est. Priority Date: 12/15/2009
• Status: Active Grant

• Current Assignee: LG Display Co., Ltd.
• Original Assignee: LG Display Co., Ltd.
• Inventors: Kim, Jonghoon
• Primary Examiner(s): EURICE, MICHAEL
• Application Number:
  US12/777,701
• Publication Number:
  US 20110141002A1
• Time in Patent Office: 2,030 Days
• Field of Search: 345/50, 345 87- 90, 345/102, 345/207, 345/100, 345/690
• US Class Current: 1/1
• CPC Class Codes: G09G 2310/0237 Switching ON and OFF the backlight within one frame
• CPC Class Codes: G09G 2310/024 Scrolling of light from the illumination source over the display in combination with the scanning of the display screen
• CPC Class Codes: G09G 2320/0261 in the context of movement of objects on the screen or movement of the observer relative to the screen
• CPC Class Codes: G09G 2320/0271 Adjustment of the gradation levels within the range of the gradation scale, e.g. by redistribution or clipping
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2320/0646 Modulation of illumination source brightness and image signal correlated to each other
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: G09G 3/342 using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines
• CPC Class Codes: G09G 3/3426 the different display panel areas being distributed in two dimensions, e.g. matrix

Abstract

A liquid crystal display includes a liquid crystal display panel, a backlight unit including a plurality of light sources, the backlight unit configured to provide light to the liquid crystal display panel, a light source driving unit configured to drive the light sources of the backlight unit using a backlight control signal, and a backlight controller configured to select a backlight dimming value depending on an input image and vary an off-start time of the backlight control signal based on the backlight dimming value.

Claims

1. A liquid crystal display, comprising:

a liquid crystal display panel;

a backlight unit comprising a plurality of light sources arranged along a first direction, each of the plurality of light sources extending in a second direction perpendicular to the first direction to provide light to a section of the liquid crystal display panel;

a light source driving unit configured to receive backlight control signals, each of the backlight control signals indicating on-times and off-times of a corresponding light source, the light source driving unit further configured to turn on or off each of the plurality of light sources of the backlight unit according to a corresponding backlight control signal; and

a backlight controller configured to;

select backlight dimming values for blocks of an input image, the blocks arranged in the first direction and the second direction;

calculate average dimming values based on the selected backlight dimming values, each average dimming value calculated for a subset of blocks of the input image to be displayed on a section of the liquid crystal display panel that is provided with light by each of the light sources; and

generate backlight control signals to operate the plurality of light sources, a duty ratio of each of the backlight control signals corresponding to each of the light sources increased responsive to increasing of each average dimming value of the subset of blocks of the input image and decreased responsive to decreasing of each average dimming value, a phase of each of the backlight control signals delayed responsive to increasing of each average dimming value, the phase advanced responsive to decreasing of each average dimming value.

2. The liquid crystal display of claim 1, wherein each of the backlight control signals comprises at least one of a pulse width modulation (PWM) signal, pulse amplitude modulation (PAM) signal, and pulse frequency modulation (PFM) signal.

3. The liquid crystal display of claim 1, wherein the backlight controller is further configured to

progressively offset the backlight control signals to match scanning timing of corresponding light sources.

4. The liquid crystal display of claim 1, wherein the backlight controller is further configured to calculate

a gain value in each of the pixels

and compensate a pixel data by multiplying the gain value with an original pixel data.

5. The liquid crystal display of claim 1, wherein at least one of the backlight control signal indicate turning off of at least one of the light source for a single time in a frame period.

6. The liquid crystal display of claim 1, wherein the first direction is horizontal direction and the second direction is a vertical direction.

7. The liquid crystal display of claim 1, wherein a blurred edge time (BET) is decreased by advancing the phase when the duty ratio is decreased.

8. The liquid crystal display of claim 1, wherein each of the backlight control signals is a digital signal.

9. The liquid crystal display of claim 8, wherein the light source driving unit is configured to receive the backlight control signals and generate pulse width modulation (PWM) signals based on the backlight control signals.

10. A method of driving a liquid crystal display, the method compromising:

receiving an input image;

selecting backlight dimming values for blocks of the input image, the blocks arranged in a first direction and a second direction;

calculating average dimming values based on the selected backlight dimming values, each average dimming value calculated for a subset of blocks of the input image to be displayed on a section of a liquid crystal panel that is provided with light by each of the light sources;

generating backlight control signals, a duty ratio of each of the backlight control signals corresponding to each of the light sources increased responsive to increasing of each average dimming value of the subset of blocks of the input image and decreased responsive to decreasing of each average dimming value, a phase of each of the backlight control signals delayed responsive to increasing of each average dimming value, the phase advanced responsive to decreasing of each average dimming value; and

turning on or turning off each of a plurality of light sources arranged behind a liquid crystal display unit along the first direction at times as indicated by a corresponding backlight control signal, each of the plurality of light sources extending in the second direction.

11. The method of claim 10, wherein the backlight control signal comprises at least one of a pulse width modulation (PWM) signal, pulse amplitude modulation (PAM) signal, and pulse frequency modulation (PFM) signal.

12. The method of claim 10, wherein at least one of the backlight control signal indicate turning off of at least one of the light source for a single time in a frame period.

13. The method of claim 10, wherein the first direction is horizontal direction and the second direction is a vertical direction.

14. The method of claim 10, wherein a blurred edge time (BET) is decreased by advancing the phase when the duty ratio is decreased.

15. The method of claim 10, wherein each of the backlight control signals is a digital signal.

16. The method of claim 15, further comprising generating pulse width modulation (PWM) signals based on the backlight control signals.