Ambient light sensing circuit and flat panel display including ambient light sensing circuit

• US 20090015166A1
• Filed: 12/26/2007
• Published: 01/15/2009
• Est. Priority Date: 12/27/2006
• Status: Active Grant

• Current Assignee: Industry-University Cooperation Foundation Hanyang University, Samsung Display Company Limited (Samsung Electronics Co. Ltd.)
• Original Assignee: Iucf-hyu Industry-university Cooperation Foundation Hanyang University, Samsung SDI Company Limited
• Inventors: Kwon, Ohkyong
• Granted Patent: US 7,859,486 B2
• Time in Patent Office: Days
• US Class Current: 315/156
• CPC Class Codes: G01J 1/4204 with determination of ambient light solar light G01J2001/4266
• CPC Class Codes: G01J 1/46 using a capacitor
• CPC Class Codes: G09G 2300/0852 being a dynamic memory with more than one capacitor
• CPC Class Codes: G09G 2300/0861 with additional control of the display period without amending the charge stored in a pixel memory, e.g. by means of additional select electrodes
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• CPC Class Codes: G09G 2360/144 the light being ambient light
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence
• CPC Class Codes: H04N 5/58 in dependence upon ambient light

Abstract

An ambient light sensing circuit includes a transistor, a first storage capacitor coupled to the transistor and adapted to compensate for a threshold voltage of the transistor, a second storage capacitor coupled to the first storage capacitor, a photodiode coupled to the first storage capacitor and the second storage capacitor and adapted to change a coupling voltage of the first and second storage capacitors based on ambient light incident thereon, a first switch adapted to selectively apply the first power supply voltage to the output load coupled to the transistor, and a second switch coupled to a first electrode of the transistor and the output load, and adapted to allow a charge stored in the storage capacitor to be discharged through the transistor based on the coupling voltage of the first storage capacitor and the second storage capacitor.

Claims

1. An ambient light sensing circuit adapted to be electrically coupled to a first power supply for supplying a first power supply voltage and an output load coupled to a storage capacitor, the ambient light sensing circuit comprising:

a transistor;

a first storage capacitor coupled to the transistor and adapted to compensate for a threshold voltage of the transistor;

a second storage capacitor coupled to the first storage capacitor;

a photodiode coupled to the first storage capacitor and the second storage capacitor, the photodiode being adapted to change a coupling voltage of the first storage capacitor and the second storage capacitor based on ambient light incident thereon;

a first switch adapted to selectively apply the first power supply voltage to the output load coupled to the transistor; and

a second switch including a first electrode coupled to a first electrode of the transistor, and a second electrode coupled to the output load and a first electrode of the first switch, the second switch being adapted to allow a charge stored in the storage capacitor to be discharged through the transistor based on the coupling voltage of the first storage capacitor and the second storage capacitor.

2. The ambient light sensing circuit as claimed in claim 1, further comprising:

a third switch including a first electrode coupled to a first electrode of the first storage capacitor and adapted to controllably supply a reference voltage to the first storage capacitor; and

a fourth switch coupled to a second electrode of the first storage capacitor and between a control electrode of the transistor and a second electrode of the transistor, and adapted to allow an adjusted reference voltage based on the threshold voltage of the transistor to be applied to the second electrode of the first storage capacitor and to selectively connect the transistor in a diode-coupled state.

3. The ambient light sensing circuit as claimed in claim 2, further comprising a fifth switch coupled to the first electrode of the transistor and adapted to supply a reference voltage to the transistor, wherein the adjusted reference voltage is based on the reference voltage supplied via the fifth switch and the threshold voltage of the transistor.

4. The ambient light sensing circuit as claimed in claim 1, further comprising a sixth switch coupled to a second electrode of the transistor and adapted to allow the storage capacitor coupled to the output load to be at least partially discharged to a second power supply based on the coupling voltage of the first storage capacitor and the second storage capacitor.

5. The ambient light sensing circuit as claimed in claim 1, further comprising a third storage capacitor coupled to the photodiode and adapted to increase an inverse bias potential of the photodiode.

6. The ambient light sensing circuit as claimed in claim 5, further comprising a seventh switch arranged between the third storage capacitor and the photodiode and adapted to couple the third storage capacitor to the photodiode in parallel.

7. The ambient light sensing circuit as claimed in claim 1, wherein the photodiode is one of a PIN diode, a PN diode, and a photo coupler, in which a cathode thereof is coupled to a reference power supply and an anode thereof is coupled to a second power supply.

8. The ambient light sensing circuit as claimed in claim 1, wherein the photodiode is one of a PIN diode, a PN diode, and a photo coupler, in which a cathode thereof is coupled to a second power supply and an anode thereof is coupled to a reference power supply.

9. The ambient light sensing circuit as claimed in claim 1, wherein the first electrode of the transistor is coupled to an ambient light control processor.

10. The ambient light sensing circuit as claimed in claim 9, wherein the ambient light control processor includes:

an analog-digital converter that is electrically coupled with the first electrode of the transistor;

a first memory that is electrically coupled with the analog-digital converter and stores a digital value in accordance with present ambient light;

a controller that is electrically coupled with the first memory and calculates and outputs brightness of the present ambient light; and

a second memory that is electrically coupled with the controller and has predetermined digital values corresponding to ambient light of various brightness levels stored therein.

11. The ambient light sensing circuit as claimed in claim 10, wherein the analog-digital converter comprises:

the output load coupled to the transistor, and

the storage capacitor coupled to the output load, wherein the storage capacitor is coupled between the output load and the second power supply.

12. The ambient light sensing circuit as claimed in claim 1, wherein the storage capacitor coupled to the output load is a parasitic wire capacitance.

13. A flat panel display, comprising:

an ambient light sensing circuit adapted to be electrically coupled to a first power supply for supplying a first power supply voltage and an output load coupled to a storage capacitor, the ambient light sensing circuit including;

a transistor;

a first storage capacitor coupled to the transistor and adapted to compensate for a threshold voltage of the transistor;

a second storage capacitor coupled to the first storage capacitor;

a photodiode coupled to the first storage capacitor and the second storage capacitor, and adapted to change a coupling voltage of the first storage capacitor and the second storage capacitor based on ambient light incident thereon;

a first switch adapted to selectively apply the first power supply voltage to the output load coupled to the transistor; and

a second switch including a first electrode coupled to a first electrode of the transistor, and a second electrode coupled to the output load and a first electrode of the first switch, the second switch being adapted to allow a charge stored in the storage capacitor to be discharged through the transistor based on the coupling voltage of the first storage capacitor and the second storage capacitor;

an ambient light control processor coupled to the second electrode of the second switch of the ambient light sensing circuit, and adapted to calculate an amount of present ambient light based on an analog signal supplied from the first electrode of the transistor and to output a digital value corresponding to the amount of present ambient light; and

a timing controller that outputs a control corresponding to the present ambient light based on the digital value output by the ambient light control processor.

14. The flat panel display as claimed in claim 13, further comprising:

a data driver that outputs a data signal corresponding to the present ambient light based on the control signal output by the timing controller; and

an organic light emitting display panel that emits light based on the data signal output by the data driver.

15. The flat panel display as claimed in claim 14, wherein the data signal output by the data driver is a data voltage that is proportional to the present ambient light sensed by the ambient light sensing circuit.

16. The flat panel display as claimed in claim 13, wherein the timing controller comprises:

a lookup table including predetermined digital values corresponding to ambient light of various brightness levels stored therein; and

a brightness selector that compares the digital value output by the ambient light control processor with the predetermined digital values stored in the lookup table, selects a control signal corresponding to the present ambient light, and outputs the control signal corresponding to the present ambient light.

17. The flat panel display as claimed in claim 13, further comprising:

an emission control driver that outputs a light emission control signal corresponding to the present ambient light based on the control signal output by the timing controller; and

an organic light emitting display panel that emits light based on the light emission control signal output by the light emission control driver.

18. The flat panel display as claimed in claim 17, wherein the light emission control signal output by the light emission control driver controls an on-time of a light emission control signal supplied to the organic light emitting display panel, and the on-time of the light emission control signal is proportional to the present ambient light sensed by the ambient light sensing circuit.

19. The flat panel display as claimed in claim 13, further comprising:

a power supply controller that outputs a power supply voltage corresponding to the present ambient light based on the control signal output by the timing controller; and

an organic light emitting display panel that emits light based on the power supply voltage output by the power supply controller.

20. The flat panel display as claimed in claim 13, further comprising:

a buffer that boosts and outputs a power supply voltage corresponding to the present ambient light based on the control signal output by the timing controller;

a backlight that is lighted by a voltage supplied from the buffer; and

a liquid crystal display panel that displays an image using light emitted from the backlight.