Apparatus and method for automatic brightness control for use in liquid crystal display device

• US 20020122020A1
• Filed: 09/25/2001
• Published: 09/05/2002
• Est. Priority Date: 12/29/2000
• Status: Active Grant

• Current Assignee: Samsung Display Company Limited (Samsung Electronics Co. Ltd.)
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Moon, Seung-Hwan, Kim, Sang-Soo, Park, Dong-Won, Choi, Hyeong-Bae
• Granted Patent: US 6,762,742 B2
• Time in Patent Office: Days
• US Class Current: 345/89
• CPC Class Codes: G09G 2320/0238 Improving the black level
• 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 2320/0606 Manual adjustment
• CPC Class Codes: G09G 2320/0613 The adjustment depending on the type of the information to be displayed
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2320/0653 Controlling or limiting the speed of brightness adjustment of the illumination source
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: G09G 3/3413 Details of control of colour illumination sources

Abstract

An LCD device having a backlight generates a backlight brightness control signal in response to a duty rate signal corresponding to an average gray level or/and a color state of image data to be displayed on the LCD device and a brightness control voltage generated from the main body of the computer by user, and controls a brightness of the backlight automatically according to the backlight brightness control signal.

Claims

1. An apparatus for automatic brightness control for use in an LCD device having a backlight, comprising:

control signal generating means for receiving an image data to be displayed on the LCD device, calculating an average gray level of the image data, and generating a brightness control signal in proportion to the average gray level; and

an inverter for automatically controlling brightness of the backlight in response to the brightness control signal from said control signal generating means.

2. The apparatus for automatic brightness control according to claim 1, wherein said control signal generating means is one selected from a timing controller, a graphic controller, and an LCD panel.

3. An apparatus for automatic brightness control for use in an LCD device having a backlight, comprising:

first control signal generating means for receiving an image data to be displayed on the LCD device, calculating an average gray level of the image data, and generating a first brightness control signal in proportion to the average gray level;

second control signal generating means for generating a second brightness control signal to control brightness of the backlight by user operation;

third control signal generating means for generating a third brightness control signal in response to the first brightness control signal and the second brightness control signal from said first control signal generating means and said second control signal generating means; and

an inverter for controlling the brightness of the backlight in response to the third brightness control signal from said third control signal generating means.

4. The apparatus for automatic brightness control according to claim 3, wherein said first control signal generating means is one selected from a timing controller, a graphic controller, and a LCD panel, and said second control signal generating means is a computer.

5. The apparatus for automatic brightness control according to claim 3, wherein said third control signal generating means includes:

a gating circuit for selectively outputting the second brightness control signal generated from said second control signal generating means when the first brightness control signal generated from said first control signal generating means is a high level; and

an R-C circuit for accumulating the second brightness control signal outputted selectively from the gating circuit, and generating the third brightness control signal.

6. The apparatus for automatic brightness control according to claim 5, wherein said R-C circuit includes:

a resistor connected between said first control signal generating means and said inverter; and

a capacitor connected between the resistor and ground.

7. The apparatus for automatic brightness control according to claim 5, wherein said gating circuit includes a transistor having one end connected through a first resistor to said first control signal generating means, another end connected with said second control signal generating means and the other end connected through a second resistor to ground.

8. The apparatus for automatic brightness control according to claim 7, wherein the transistor is one selected from an N-type transistor and a P-type transistor.

9. The apparatus for automatic brightness control according to claim 7, wherein the transistor can be a circuit element such as a calculation amplifier.

10. The apparatus for automatic brightness control according to claim 8, further including a level shift circuit for swinging the transistor fully by lowering a voltage level of the first brightness control signal outputted from said first control signal generating means as much as a given level when the transistor is a P-type transistor.

11. The apparatus for automatic brightness control according to claim 10, wherein the level shift circuit includes:

a transistor having a current passage connected in serial between a power source for supplying voltage and said third control signal generating means, and a control end connected to said first control signal generating means;

a third resistor connected in serial to the current passage of said transistor;

a diode connected in serial between said third resistor and the ground; and

a fourth resistor connected in parallel with said diode.

12. The apparatus for automatic brightness control according to claim 3, wherein the third brightness control signal forming a variable brightness control voltage satisfies the following formula:

Vduty={Vo+(Vc−

Vo)×

[1−

EXP[−

T1/(R×

C)]]}×

EXP[(T1−

1H)/(R×

C)]

13. The apparatus for automatic brightness control according to claim 3, wherein said control signal generating means further includes a function that determines a color state of the image data and then make the brightness control signal to have a duty rate for controlling the brightness of the backlight corresponding to the determined color state.

14. The apparatus for automatic brightness control according to claim 13, wherein said duty rate of said brightness control signal is reduced in order of green, red, and blue when the determined color state is green, red, and blue.

15. The apparatus for automatic brightness control according to claim 14, wherein the duty rate of the brightness control signal is set to have a rate of green:

red;

blue=1;

0.66;

0.49 when the determined color state is green, red, and blue.

16. The apparatus for automatic brightness control according to claim 14, wherein said control signal generating means is a timing controller.

17. The apparatus for automatic brightness control according to claim 14, wherein said control signal generating means includes:

a control unit for controlling various operations of said control signal generating means to determine the color state of the image data and to generate the brightness control signal;

a pixel data acquisition and conversion unit for receiving the image data and converting the image data according to the determined color state, under the control of said control unit;

a computing unit for computing the converted data logically and outputting a certain data, under the control of said control unit;

a down-counter for down-counting the certain data under the control of said control unit; and

a pulse generator for generating the brightness control signal corresponding to an output signal of said down-counter, wherein said control unit controls to generate the brightness control signal corresponding to the output signal of said down-counter until it comes to a logic low level.

20. The apparatus for automatic brightness control according to claim 19, wherein the brightness control signal has a duty rate reduced in order of green, red, and blue when the determined color state is green, red, and blue.

21. The apparatus for automatic brightness control according to claim 20, wherein the duty rate of the brightness control signal is set to have a rate of green:

red;

blue=1;

0.66;

0.49 when the determined color state is green, red, and blue.

22. The apparatus for automatic brightness control according to claim 20, wherein said control signal generating means is a timing controller.

23. The apparatus for automatic brightness control according to claim 20, wherein said control signal generating means includes:

a control unit for controlling various operations of said control signal generating means to determine the color state of the pixel data and to generate the brightness control signal;

a pixel data acquisition and conversion unit for receiving the pixel data from the host and converting the pixel data according to the determined color state, under the control of said control unit;

a computing unit for computing the converted data logically and outputting a certain data, under the control of said control unit;

a down-counter for down-counting the certain data under the control of said control unit; and

a pulse generator for generating the brightness control signal corresponding to an output signal of said down-counter,

wherein said control unit controls to generate the brightness control signal corresponding to the output signal of said down-counter until it comes to a logic low level.

25. The method for automatic brightness control according to claim 24, wherein said converting step further comprises converting said pixel data to have a duty rate corresponding to a brightness reduced in order of green, red, and blue when the determined color state is green, red, and blue.

26. The method for automatic brightness control according to claim 25, wherein the pixel data are converted into data corresponding to 100%, 66% and 49% of the maximum brightness when the determined color state is green, red, and blue, respectively.

18. A method for automatic brightness control for use in an LCD device, comprising the steps of:

calculating an average gray level of image data to be displayed on said LCD device;

generating a first brightness control signal in proportion to the average gray level;

generating a second brightness control signal generated from the main body of the computer;

generating a third brightness control signal in response to the first brightness control signal and the second brightness control signal; and

controlling a brightness of said backlight in response to said third brightness control signal.

19. An apparatus for automatic brightness control for use in an LCD device having a backlight used with a host of outputting a video information, comprising:

control signal generating means for receiving a pixel data corresponding to said video information, determining a color state of said pixel data, and generating a brightness control signal having a duty rate for controlling a brightness of the backlight to correspond to the determined color state; and

an inverter for controlling the brightness of the backlight automatically in response to said brightness control signal from said control signal generating means.

24. A method for automatic brightness control for use in an LCD device having a backlight used with a host of outputting a video information, comprising the steps of:

receiving a pixel data corresponding to the video information;

determining a color state of the pixel data;

converting the pixel data according to the determined color state;

determining whether the pixel data is a last data of one horizontal line period;

outputting a brightness control signal corresponding to the pixel data when the pixel data is the last data of one horizontal line period; and

controlling a brightness of the backlight in response to the brightness control signal.