Ambient light detection circuit

• US 20050127278A1
• Filed: 12/15/2003
• Published: 06/16/2005
• Est. Priority Date: 12/15/2003
• Status: Active Grant

• Current Assignee: Eastman Kodak Company
• Original Assignee: Eastman Kodak Company
• Inventors: Cok, Ronald S.
• Granted Patent: US 7,271,378 B2
• Time in Patent Office: Days
• US Class Current: 250/214.AL
• 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: G02F 1/13318 Circuits comprising a photodetector
• CPC Class Codes: G02F 1/133603 with LEDs

Abstract

A circuit for detecting light is disclosed comprising: a) a light-integrating photo-sensor circuit having one or more thin-film photosensors and being responsive to a variable integration period signal and to ambient light for producing a photo signal representing the intensity of the ambient light, wherein the photo signal may be in one of at least three states including a no-signal state, an in-range state, and a saturated state; and b) a control circuit for receiving the photo signal and automatically increasing the period of the integration period signal when the photo signal is in the no-signal state and decreasing the period of the integration period signal when the photo signal is in the saturated state so as to result in the photo signal being in the in-range state and producing a corresponding ambient light signal. In particular embodiments of the invention, the circuit for detecting light is employed as a component of a flat panel display, and the ambient light signal is used for adjusting the brightness of the flat-panel display. The invention enables an improved dynamic range for thin-film photosensors, particularly when used with a flat-panel display.

Claims

1. A circuit for detecting light comprising:

a) a light-integrating photo-sensor circuit having one or more thin-film photosensors and being responsive to a variable integration period signal and to ambient light for producing a photo signal representing the intensity of the ambient light, wherein the photo signal may be in one of at least three states including a no-signal state, an in-range state, and a saturated state; and

b) a control circuit for receiving the photo signal and automatically increasing the period of the integration period signal when the photo signal is in the no-signal state and decreasing the period of the integration period signal when the photo signal is in the saturated state so as to result in the photo signal being in the in-range state and producing a corresponding ambient light signal.

2. The circuit claimed in claim 1, wherein the photosensor is a photodiode.

3. The circuit claimed in claim 1, wherein the photosensor is a photo capacitor.

4. The circuit claimed in claim 1, wherein the photosensor is a phototransistor.

5. The circuit claimed in claim 1, wherein the photosensor is an organic photosensor.

6. The circuit claimed in claim 1, wherein the photosensor is a silicon photosensor.

7. The circuit claimed in claim 1, wherein the photo-signal states are represented by digital signals.

8. The circuit claimed in claim 1, wherein the photo-signal states are represented by analog signals.

9. The circuit claimed in claim 1, wherein the value of the integration period signal is stored as a digital value.

10. The circuit claimed in claim 1, wherein the integration period signal is generated by a digital counter.

11. The circuit claimed in claim 1 further comprising a plurality of photosensor circuits producing a plurality of respective photo signals and wherein the control circuit is responsive to the plurality of photo signals.

12. A flat-panel display, comprising

a) a substrate and a plurality of light-emitting elements located thereon in a display area;

and

b) a circuit for detecting light incident on the flat-panel display comprising;

i) a light-integrating photo-sensor circuit having one or more thin-film photosensors located on the substrate and being responsive to a variable integration period signal and to ambient light for producing a photo signal representing the intensity of the ambient light incident on the flat-panel display, wherein the photo signal may be in one of at least three states including a no-signal state, an in-range state, and a saturated state; and

ii) a control circuit for receiving the photo signal and automatically increasing the period of the integration period signal when the photo signal is in the no-signal state and decreasing the period of the integration period signal when the photo signal is in the saturated state so as to result in the photo signal being in the in-range state and producing a corresponding ambient light signal.

13. The circuit claimed in claim 12, wherein the photosensor circuit includes a detector circuit and wherein the detector circuit and/or the control circuit is a thin-film device located on the substrate.

14. The circuit claimed in claim 12, wherein the photosensor circuit includes a detector circuit and wherein the detector circuit and/or the control circuit are located externally to the substrate.

15. The flat-panel display claimed in claim 12, wherein the display area is rectangular and the photosensor is located at an edge or a corner of the rectangular display area.

16. The display claimed in claim 12, wherein the light emitting elements are organic light emitting diodes.

17. The display claimed in claim 12 further comprising a plurality of photosensor circuits producing a plurality of respective photo signals and wherein the control circuit is responsive to the plurality of photo signals.

18. A method for controlling a flat-panel display, comprising:

a) providing a flat-panel display comprising a substrate and a plurality of light-emitting elements located thereon in a display area;

b) providing a light-integrating photo-sensor circuit having one or more thin-film photosensors located on the substrate and responding to a variable integration period signal and to ambient light for producing a photo signal representing the intensity of the ambient light incident on the flat-panel display, wherein the photo signal may be in one of at least three states including a no-signal state, an in-range state, and a saturated state;

c) iteratively receiving the photo signal and automatically increasing the period of the integration signal when the photo signal is in the no-signal state and decreasing the period of the integration signal when the photo signal is in the saturated state so as to result in the photo signal being in the in-range state and producing a corresponding ambient light signal; and

d) adjusting the brightness of the flat-panel display in response to the ambient light signal.