Light sensing circuit, backlight control apparatus having the same, and liquid crystal display device having the same

• US 20070296687A1
• Filed: 12/28/2006
• Published: 12/27/2007
• Est. Priority Date: 06/23/2006
• Status: Active Grant

• Current Assignee: LG Display Co., Ltd.
• Original Assignee: LG Philips LCD Company Limited (LG Display Co., Ltd.)
• Inventors: Yoon, Jeong-Won, Moon, Su-Hwan
• Granted Patent: US 7,804,481 B2
• Time in Patent Office: Days
• US Class Current: 345/102
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2360/144 the light being ambient light
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336

Abstract

A light sensing circuit capable of enhancing a reliability by lowering a dependency on a temperature change without using a resistor, a backlight control apparatus having the same, and an LCD device having the same. The light sensing circuit includes a first MOS-transistor; and a second MOS-transistor serially connected to the first MOS-transistor between a first power terminal and a ground terminal, in which a second power terminal is connected to each gate terminal of the first MOS-transistor and the second MOS-transistor, and an optical amount detecting terminal is connected to a common connection point between a drain terminal of the first MOS-transistor and a source terminal of the second MOS-transistor.

Claims

1. A light sensing circuit, comprising:

a first metal oxide semiconductor (MOS)-transistor; and

a second MOS-transistor serially connected to the first MOS-transistor between a first power terminal and a ground terminal,

wherein a second power terminal is connected to each gate terminal of the first MOS-transistor and the second MOS-transistor, and an optical amount detecting terminal is connected to a common connection point between a drain terminal of the first MOS-transistor and a source terminal of the second MOS-transistor.

2. The light sensing circuit of claim 1, wherein the first MOS-transistor and the second MOS-transistor respectively comprise an amorphous-silicon type MOS-transistor.

3. The light sensing circuit of claim 1, wherein the first MOS-transistor and the second MOS-transistor are disposed at an edge of an LC panel.

4. The light sensing circuit of claim 1, wherein the first MOS-transistor is disposed so as to be exposed to external light, and the second MOS-transistor is disposed so as not to be exposed to external light.

5. The light sensing circuit of claim 1, further comprising a black matrix for shielding external light positioned at an upper portion of the second MOS-transistor.

6. The light sensing circuit of claim 1, further comprising an optical amount detecting terminal (V_d) connected to the a common connection point.

7. A liquid crystal display (LCD) device, comprising:

an LC panel;

a backlight that irradiates light a rear side of the LC panel;

an inverter that supplies an output power to the backlight;

a light sensing circuit that detects an amount of external light introduced to the LC panel by a first metal oxide semiconductor (MOS)-transistor and a second MOS-transistor serially connected to each other; and

an inverter driving controller that controls a driving of an inverter based on a voltage corresponding to the optical amount from the light sensing circuit.

8. The LCD device of claim 7, further comprising a second power terminal connected to each gate terminal of the first MOS-transistor and the second MOS-transistor, and an optical amount detecting terminal connected to a common connection point between a drain terminal of the first MOS-transistor and a source terminal of the second MOS-transistor, wherein the light sensing circuit is constructed so that the first MOS-transistor and the second MOS-transistor are serially connected to each other between a first power terminal and a ground terminal.

9. The LCD device of claim 7, wherein the first MOS-transistor and the second MOS-transistor comprise an amorphous-silicon type MOS-transistor.

10. The LCD device of claim 7, wherein the first MOS-transistor and the second MOS-transistor are disposed at an edge of an LC panel.

11. The LCD device of claim 7, wherein the first MOS-transistor is disposed so as to be exposed to external light, and the second MOS-transistor is disposed so as not to be exposed to external light.

12. The LCD device of claim 11, wherein the LC panel comprises:

a lower substrate on which the first MOS-transistor and the second MOS-transistor are formed;

an upper substrate adjacent the lower substrate, and comprising a black matrix of a lattice shape thereon; and

an LC layer positioned between the upper substrate and the lower substrate,

wherein the black matrix is disposed on the upper substrate corresponding to the second MOS-transistor, and the black matrix is removed on the upper substrate corresponding to the first MOS-transistor.

13. The LCD device of claim 12, further comprising a polarizer respectively coupled onto an outer surface of the upper substrate and an outer surface the lower substrate, and wherein the polarizer attached onto the lower substrate is removed at a region corresponding to the first MOS-transistor.

14. The LCD device of claim 8, wherein an optical amount detecting terminal is connected to the common connection point.

15. A backlight control apparatus for controlling a backlight to irradiate light to a rear side of an LC panel, the apparatus comprising:

a light sensing circuit that detects an amount of external light introduced into the LC panel by a first MOS-transistor and a second MOS-transistor serially connected to each other, and outputs a voltage corresponding to the detected optical amount;

an inverter that supplies an output power to the backlight; and

an inverter driving controller that controls a driving of the inverter according to the voltage output from the light sensing circuit.

16. A liquid crystal display (LCD) device, comprising:

an LC panel;

means for irradiating a rear side of the LC panel;

means for supplying an output power to the backlight;

means for detecting an amount of external light introduced to the LC panel by a first metal oxide semiconductor (MOS)-transistor and a second MOS-transistor serially connected to each other; and

means for controlling a driving of an inverter based on a voltage corresponding to the optical amount from the light sensing circuit.

17. The LCD device of claim 16, further comprising a second power terminal connected to each gate terminal of the first MOS-transistor and the second MOS-transistor, and an optical amount detecting terminal connected to a common connection point between a drain terminal of the first MOS-transistor and a source terminal of the second MOS-transistor, wherein the light sensing circuit is constructed so that the first MOS-transistor and the second MOS-transistor are serially connected to each other between a first power terminal and a ground terminal.

18. The LCD device of claim 16, wherein the first MOS-transistor and the second MOS-transistor comprise an amorphous-silicon type MOS-transistor.

19. The LCD device of claim 16, wherein the first MOS-transistor and the second MOS-transistor are disposed at an edge of an LC panel.

20. The LCD device of claim 16, wherein the first MOS-transistor is disposed so as to be exposed to external light, and the second MOS-transistor is disposed so as not to be exposed to external light.

21. The LCD device of claim 20, wherein the LC panel comprises:

a lower substrate on which the first MOS-transistor and the second MOS-transistor are formed;

an upper substrate adjacent the lower substrate, and comprising a black matrix of a lattice shape thereon; and

an LC layer positioned between the upper substrate and the lower substrate,

wherein the black matrix is disposed on the upper substrate corresponding to the second MOS-transistor, and the black matrix is removed on the upper substrate corresponding to the first MOS-transistor.

22. The LCD device of claim 21, further comprising a polarizer respectively coupled onto an outer surface of the upper substrate and an outer surface the lower substrate, and wherein the polarizer attached onto the lower substrate is removed at a region corresponding to the first MOS-transistor.

23. The LCD device of claim 19, wherein an optical amount detecting terminal is connected to the common connection point.

24. A backlight control apparatus for controlling a backlight to irradiate light to a rear side of an LC panel, the apparatus comprising:

light sensing means for detecting an amount of external light introduced into the LC panel by a first MOS-transistor and a second MOS-transistor serially connected to each other, and outputs a voltage corresponding to the detected optical amount;

means for supplying an output power to the backlight; and

means for controlling a driving of the inverter according to the voltage output from the light sensing circuit.