Apparatus and method for eliminating artifacts in active pixel sensor (APS) imagers

• US 8,063,965 B2
• Filed: 06/27/2008
• Issued: 11/22/2011
• Est. Priority Date: 03/09/1999
• Status: Expired due to Fees

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Micron Technology, Inc.
• Inventors: Wang, Yibing (Michelle)
• Primary Examiner(s): Tran; Sinh
• Assistant Examiner(s): Peterson; Christopher K
• Application Number:
  US12/216,033
• Publication Number:
  US 20090015700A1
• Time in Patent Office: 1,243 Days
• Field of Search: 348308-310, 348/303, 348/246, 348/247, 348/294, 348/302
• US Class Current: 348/308
• CPC Class Codes: H04N 23/76 by influencing the image signals
• CPC Class Codes: H04N 25/627 Detection or reduction of inverted contrast or eclipsing effects
• CPC Class Codes: H04N 25/75 Circuitry for providing, modifying or processing image signals from the pixel array
• CPC Class Codes: H04N 25/78 Readout circuits for addressed sensors, e.g. output amplifiers or A/D converters

Abstract

An active pixel sensor (APS) that includes circuitry to eliminate artifacts in digital images. The APS includes a comparator for comparing a signal level from a pixel to an adjusted saturation voltage to determine if the pixel is saturated. If the pixel is saturated, the signal output from the pixel is replaced with an analog voltage having a maximum value corresponding to a brightest pixel in the image.

Claims

1. An imaging device comprising:

a pixel comprising a photo detector; and

a readout circuit coupled to said pixel, said readout circuit providing a first pixel signal representing a reset voltage of said pixel and a second pixel signal representing light incident voltage produced from said photo detector;

a circuit for producing a pixel output voltage from said first and second pixel voltage signals;

a detecting circuit for determining when said pixel is in at least a near saturated condition; and

a circuit responsive to said detecting circuit for substituting a different pixel output voltage for a produced pixel output voltage when said at least near saturated condition is detected.

2. The imaging device as in claim 1, further comprising an analog to digital converter for converting a pixel output voltage to a digital value.

3. The imaging device as in claim 1, wherein said detecting circuit compares a voltage level of said second signal to a reference voltage level to determine said at least near saturated condition.

4. The imaging device as in claim 1, wherein said at least near saturated condition is associated with a drop in said first pixel signal reset voltage.

5. The imaging device as in claim 1, wherein said different pixel output voltage represents a predetermined brightness level.

6. The imaging device as in claim 5, wherein said predetermined brightness level is a highest brightness level which said producing circuit can produce without said pixel being in a saturated condition.

7. An imaging device comprising:

a pixel comprising a photo detector; and

a readout circuit coupled to said photo detector, said readout circuit providing a first pixel signal representing a reset voltage of said pixel and a second pixel signal representing light incident voltage produced from said photo detector;

a circuit for producing a pixel output signal voltage from said first and second pixel voltage signals;

a circuit responsive to a signal produced by said pixel for detecting at least a near saturated pixel condition; and

a circuit responsive to said detecting circuit for changing said pixel output voltage when said at least near saturated condition is detected.

8. An active pixel sensor comprising:

a pixel comprising a photo detector and readout circuit for providing respective output signals representing a pixel voltage reset and a pixel detected light voltage;

a circuit for producing a pixel output voltage based on said reset voltage and detected light voltage;

a detecting circuit for determining when said pixel is in an at least near saturated condition; and

a circuit for substituting a predetermined output signal voltage for said pixel output signal voltage when said at least near saturated condition is detected.

9. An active pixel sensor, comprising:

a pixel comprising a photodiode to receive light, the pixel to provide a pixel value;

a first circuit to compare the pixel value to a reference signal to determine if the photodiode of the pixel is at least nearly saturated by the light; and

a second circuit to provide a first signal, associated with the pixel, if the first circuit indicates that the pixel value is above the reference signal, and to provide a second signal, associated with a constant value which is independent of saturation of the photodiode by the light, if the first circuit indicates that the pixel value is below the reference signal.

10. The active pixel sensor as in claim 9, wherein the pixel value corresponds to a pixel voltage representing received light.

11. The active pixel sensor as in claim 9, wherein the first signal corresponds to a pixel received light value.

12. The active pixel sensor as in claim 11, wherein the second signal corresponds to a brightest-possible pixel value.

13. The active pixel sensor as in claim 9, wherein the first signal is dependent on saturation of the photodiode by the light.

14. The active pixel sensor as in claim 9, wherein the second signal corresponds to a brightest-possible pixel value.

15. The active pixel sensor of claim 9, wherein said pixel generates a reset signal value and an incident light signal value, and further comprising a correlated double sampling circuit for sampling said reset and incident light signal values.

16. The active pixel sensor of claim 9, further comprising an analog to digital converter for producing a digital pixel value from signals generated by said pixel.

17. The active pixel circuit of claim 16, wherein said second circuit is upstream of said analog to digital converter.

18. The active pixel circuit of claim 16, wherein said second circuit is provided downstream of said analog to digital converter.

19. An active pixel sensor comprising:

a pixel for providing a pixel voltage on a column output line;

a first circuit coupled to the column output line for comparing the pixel voltage on the column output line to a reference voltage to determine if the pixel is at least near a saturated condition;

an output circuit coupled to the column output line for providing an output signal representing the amount of light detected by the pixel when the pixel is not at least near a saturated condition; and

a circuit coupled to the first circuit for substituting a constant voltage for the output signal when the pixel is at least near a saturated condition.

20. An active pixel sensor, comprising:

a pixel comprising a photodiode to receive light, the pixel to provide a pixel value;

a comparator to compare the pixel value to a reference signal to determine if the photodiode of the pixel is at least nearly saturated by the light;

a multiplexer to provide a first signal associated with the pixel, if the comparator indicates that the pixel value is above the reference signal, and to provide a second signal, corresponding to a predetermined value which is independent of photodiode received light, if the first circuit indicates that the pixel value is below the reference signal.

21. Am active pixel sensor as in claim 20, wherein the pixel value corresponds to a received light pixel signal voltage.

22. The active pixel sensor as in claim 20, wherein the first signal corresponds to a received light pixel value.

23. The active pixel sensor as in claim 22, wherein the second signal corresponds to a highest-possible pixel value.

24. The active pixel sensor as in claim 20, wherein the first signal is dependent on saturation of the photodiode by the light.

25. The active pixel sensor as in claim 20, wherein the second signal corresponds to a highest-possible pixel value.

26. The active pixel sensor of claim 20, wherein said pixel generates a reset signal value and an incident light signal value and further comprising a correlated double sampling circuit for sampling said reset and incident light signal values.

27. The active pixel sensor of claim 20, further comprising an analog to digital converter for producing a digital pixel value from signals generated by said pixel.

28. The active pixel circuit of claim 27, wherein said multiplexer circuit is upstream of said analog to digital converter.

29. A method comprising:

receiving light at a photodiode of a pixel in an active pixel sensor;

providing a pixel voltage value to a column output line from the pixel; and

replacing a first signal, corresponding to a pixel value, with a predetermined signal that is substantially independent of a measurement of received light if the photodiode is at least nearly saturated by light to generate a pixel voltage value corresponding to a predetermined brightness state.

30. The method of claim 29, wherein the pixel value corresponds to a pixel received light signal voltage.

31. The method of claim 29, wherein said predetermined brightness state is a highest brightness state which can be generated by a pixel.

32. The method of claim 29, wherein the first signal is dependent on saturation of the photodiode by the light.

33. The method of claim 29, wherein said pixel generates a reset pixel value and a received light pixel value which are captured in a correlated double sampling operation.

34. The method of claim 29, further comprising analog to digitally converting the first signal or the predetermined replacement signal.

35. The method of claim 29, further comprising analog to digitally converting said first signal to a digital value and performing said replacement in a digital domain.

36. The method of claim 29, further comprising comparing the pixel value to a reference value to determine if the photodiode is at least nearly saturated by the light.

37. A method comprising:

generating a pixel value from an imaging pixel;

comparing the pixel value to a reference signal to determine if said pixel is in at least a nearly saturated state;

providing a first pixel output signal if the pixel value is above the reference signal and providing a second pixel output signal corresponding to a constant value which is independent of pixel received light if the pixel value is below the reference signal.

38. The method of claim 37, wherein the pixel value corresponds to a pixel voltage representing received light.

39. The method of claim 37, wherein the first signal corresponds to a pixel received light value.

40. The method of claim 39, wherein the second signal corresponds to a brightest-possible pixel value.

41. The method of claim 39, wherein said pixel generates a reset signal value and an incident light signal value, said method further comprising performing correlated double sampling of said reset signal value and incident light signal value.

42. The method of claim 39, further comprising analog to digital converting signals generated by said pixel.

43. The method of claim 42, wherein said providing said first pixel output signal or second pixel output signal is performed before said analog to digital converting.

44. The method of claim 42, wherein said providing said first pixel output signal or second pixel output signal is performed after said analog to digital converting.

45. The method of claim 37, wherein the first signal is dependent on saturation of a photodiode of the pixel by the light.

46. The method of claim 45, wherein the second signal corresponds to a brightest-possible pixel value.

47. A method comprising:

providing a pixel voltage on a column line;

comparing the pixel voltage provided on the column line to a reference voltage to determine if the pixel is near or at a saturated condition;

providing an output signal representing the amount of light detected by the pixel when said pixel is not at least near saturation;

providing a predetermined constant value pixel output signal when the pixel is at least near saturation.

48. A method comprising:

generating a pixel value from an imaging pixel;

comparing the pixel value to a reference signal to determine if a photodiode of the pixel is at least nearly saturated by light;

providing a first signal associated with the pixel if the pixel value is above the reference signal;

providing a second signal corresponding to a predetermined value which is independent of photodiode received light, if the pixel value is below the reference signal.

49. The method of claim 48, wherein the pixel value corresponds to a received light pixel signal voltage.

50. The method of claim 48, wherein the first signal corresponds to a received light pixel value.

51. The method of claim 50, wherein the second signal corresponds to a brightest-possible pixel value.

52. The method of claim 48, the first signal is dependent on saturation of the photodiode by the light.

53. The method of claim 48, wherein the second signal corresponds to a brightest-possible pixel value.

54. The method of claim 48, wherein the pixel generates a reset signal value and an incident light signal value, said method further comprising performing a correlated double sampling of said reset signal value and incident light signal value.