Image sensor with dark signal reduction

• US 20040183928A1
• Filed: 05/23/2003
• Published: 09/23/2004
• Est. Priority Date: 03/18/2003
• Status: Active Grant

• Current Assignee: Candela Microsystems Incorporated
• Original Assignee: Candela Microsystems Incorporated
• Inventors: Tay, Hiok Nam
• Granted Patent: US 7,015,960 B2
• Time in Patent Office: Days
• US Class Current: 348/244
• CPC Class Codes: H04N 25/00 Circuitry of solid-state image sensors [SSIS]; Control thereof
• CPC Class Codes: H04N 25/63 applied to dark current

Abstract

An image sensor that has a temperature sensor. The temperature sensor senses the temperature of a pixel array of the image sensor. The sensed temperature is used to scale a dark frame image generated by the pixel array. The scaled dark frame image is subtracted from a light image frame generated by the pixel array. The scaled dark image frame compensates for temperature variations in the pixel array. The scaled dark image frame may be generated by multiplying the dark frame by a scale factor(s). The scale factor may be computed from an equation or determined from a look-up table. The equation or look-up table may compensate for thermal gradients across the pixel.

Claims

1. An image sensor, comprising:

a pixel array; and

,

a temperature sensor that senses a temperature of said pixel array.

2. The image sensor of claim 1, further comprising a memory, a dark frame estimator coupled to said memory and said temperature sensor, and a combiner coupled to said dark signal estimator and said pixel array.

3. The image sensor of claim 2, wherein said dark frame estimator multiplies a dark image frame with a scale factor, said combiner combines the scaled dark image frame with a light image frame generated by said pixel array.

4. The image sensor of claim 3, wherein the scale factor is computed from at least one equation.

5. The image sensor of claim 3, wherein the scale factor is determined from a look-up table.

6. The image sensor of claim 2, wherein said memory is coupled to said pixel array.

7. The image sensor of claim 2, wherein said memory is coupled to said temperature sensor.

8. The image sensor of claim 4, wherein the at least one equation provides a different scale factor for at least two different pixels of said pixel array.

9. The image sensor of claim 8, wherein at least one of the equations includes a polynomial.

10. The image sensor of claim 4, wherein the equation is dependent on temperature and exposure time.

11. An image sensor, comprising:

pixel array means for generating a dark image frame and a light image frame; and

,

temperature sensor means for sensing a temperature of said pixel array means during the dark image frame and the light image frame.

12. The image sensor of claim 11, further comprising memory means for storing the dark image frame.

13. The image sensor of claim 11, further comprising dark frame estimator means for multiplying the dark image frame with a scale factor, and combiner means for combining the scaled dark image frame with the light image frame.

14. The image sensor of claim 13, wherein the scale factor is computed from at least one equation.

15. The image sensor of claim 13, wherein the scale factor is determined from a look-up table.

16. The image sensor of claim 12, wherein said memory means stores at least one coefficient.

17. The image sensor of claim 14, wherein the at least one equation provides a different scale factor for at least two different pixels of said pixel array means.

18. The image sensor of claim 17, wherein at least one of the equations includes a polynomial.

19. The image sensor of claim 14, wherein the equation is dependent on temperature and exposure time.

20. An image sensor system, comprising:

a pixel array;

a temperature sensor that senses a temperature of said pixel array;

a memory;

a dark frame estimator coupled to said memory and said temperature sensor; and

,

a combiner coupled to said dark signal estimator and said pixel array.

21. The image sensor system of claim 20, wherein said pixel array and said temperature sensor are located on an integrated circuit.

22. The image sensor system of claim 20, wherein said dark frame estimator multiplies a dark image frame with a scale factor, said combiner combines the scaled dark image frame with a light image frame generated by said pixel array.

23. The image sensor system of claim 22, wherein the scale factor is computed from at least one equation.

24. The image sensor system of claim 22, wherein the scale factor is determined from a look-up table.

25. The image sensor system of claim 20, wherein said memory is coupled to said pixel array.

26. The image sensor system of claim 20, wherein said memory is coupled to said temperature sensor.

27. The image sensor system of claim 23, wherein the at least one equation provides a different scale factor for at least two different pixels of said pixel array.

28. The image sensor system of claim 27, wherein at least one of the equations includes a polynomial.

29. The image sensor system of claim 23, wherein the equation is dependent on temperature and exposure time.

30. An image sensor system, comprising:

pixel array means for generating a dark image frame and a light image frame;

temperature sensor means for sensing a temperature of said pixel array means during the light image frame;

memory means for storing the dark image frame;

dark frame estimator means for multiplying the dark image frame with a scale factor; and

,

combiner means for combining the scaled dark image frame with the light image frame.

31. The image sensor system of claim 30, wherein said pixel array means and said temperature sensor means are located on an integrated circuit.

32. The image sensor system of claim 30, wherein the scale factor is computed from at least one equation.

33. The image sensor system of claim 30, wherein the scale factor is determined from a look-up table.

34. The image sensor system of claim 32, wherein said memory means stores at least one coefficient.

35. The image sensor system of claim 32, wherein the at least one equation provides a different scale factor for at least two different pixels of said pixel array means.

36. The image sensor system of claim 35, wherein at least one of the equations includes a polynomial.

37. The image sensor system of claim 32, wherein the equation is dependent on temperature and exposure time.

38. A method for dark signal reduction in an image sensor, comprising:

sensing a temperature of a pixel array that generates a light image frame;

scaling a dark image frame in accordance with the sensed temperature; and

,

combining the scaled dark image frame with the light image frame.

39. The method of claim 38, wherein the dark image frame is scaled by multiplying the dark image frame with a scale factor.

40. The method of claim 39, wherein the scale factor is computed from an equation.

41. The method of claim 40, wherein the equation provides a different scale factor for at least two different pixels of the pixel array.

42. The method of claim 41, wherein at least one of the equations includes a polynomial.

43. The method of claim 39, wherein the scale factor is determined from a look-up table.

44. A program storage medium that can cause a processor to provide dark signal reduction in an image sensor system, comprising:

a processor readable storage medium that causes a processor of an image sensor system to scale a dark image frame based on a temperature of a pixel array sensed during the generation of light image frame, and combining the scaled dark image frame with the light image frame.

45. The storage medium of claim 44, wherein the dark image frame is scaled by multiplying the dark image frame with a scale factor.

46. The storage medium of claim 45, wherein the scale factor is computed from at least one equation.

47. The storage medium of claim 45, wherein the scale factor is determined from a look-up table.

48. The storage medium of claim 46, wherein the equation provides a different scale factor for at least two different pixels of said pixel array.

49. The storage medium of claim 48, wherein at least one of the equations includes a polynomial.

50. The storage medium of claim 46, wherein the equation is dependent on temperature and exposure time.