Ambient light detection technique for an imaging array

• US 6,469,289 B1
• Filed: 11/21/2000
• Issued: 10/22/2002
• Est. Priority Date: 01/21/2000
• Status: Expired due to Term

• Current Assignee: Cedar Lane Technologies Inc.
• Original Assignee: Symagery Microsystems, Inc. (Motorola Solutions, Inc.)
• Inventors: Vulpoiu, Paul, Roustaei, Alex, Scott-Thomas, John
• Primary Examiner(s): LE, QUE TAN
• Application Number:
  US09/718,137
• Time in Patent Office: 700 Days
• Field of Search: 250/208.1, 250/214.AL, 250/214.1, 250/214.R, 348/294, 348/295, 348/297, 348/309, 257/290, 257/291, 257/431-435
• US Class Current: 250/208.1
• CPC Class Codes: H04N 23/71 Circuitry for evaluating the brightness variation
• CPC Class Codes: H04N 23/72 Combination of two or more compensation controls
• CPC Class Codes: H04N 23/74 by influencing the scene brightness using illuminating means
• CPC Class Codes: H04N 25/00 Circuitry of solid-state image sensors [SSIS]; Control thereof
• CPC Class Codes: H04N 25/46 by combining or binning pixels
• CPC Class Codes: H04N 25/706 Pixels for exposure or ambient light measuring
• CPC Class Codes: H04N 25/76 Addressed sensors, e.g. MOS or CMOS sensors
• CPC Class Codes: H04N 25/77 Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components
• CPC Class Codes: H04N 25/779 Circuitry for scanning or addressing the pixel array
• CPC Class Codes: H04N 25/78 Readout circuits for addressed sensors, e.g. output amplifiers or A/D converters
• CPC Class Codes: H04N 3/1512 for MOS image-sensors, e.g. MOS-CCD H04N3/1581 takes precedence
• CPC Class Codes: H04N 3/155 Control of the image-sensor operation, e.g. image processing within the image-sensor
• CPC Class Codes: H04N 3/1562 for selective scanning, e.g. windowing, zooming

Abstract

This invention is directed to a method and apparatus for determining the level of ambient light impinging on a selected number of pixels in an imaging array where each pixel includes a photodiode. The ambient light may be determined by resetting the pixels in the array and by detecting current flow through the photodiodes in a selected number of the pixels as they are being reset. Alternately, the ambient light may be determined by resetting a selected number of the pixels in the array and by detecting current flow through the photodiodes in the selected number of the pixels as they are being reset. The photodiodes are reset by applying a reverse bias voltage across them and the current flow is detected by measuring the current flow through a resistance in parallel to the selected photodiodes. The selected number of pixels may be divided into one or more groups each having at least one pixel, and the pixels in each group may be arranged in specific patterns within the array. The array may be laid out in rows and columns, and the groups may be located in predetermined rows or columns. When only a selected number of pixels are reset and these pixels are divided into groups, the groups may be sequentially reset to permit differentiation between the groups.

Claims

1. A method of determining the level of ambient light impinging on a pixel having a photodiode comprising:

a. resetting the pixel; and

b. detecting the current flow through the photodiode during the resetting step to determine the ambient light level.

2. A method of determining the level of ambient light impinging on a pixel having a photodiode as claimed in claim 1 wherein the resetting step (a) includes

a.1. applying a reverse bias voltage across the photodiode.

3. A method of determining the level of ambient light impinging on a pixel having a photodiode as claimed in claim 2 wherein the detecting step (b) includes:

b.1. detecting the current flow through a resistance in parallel to the photodiode.

4. A method of determining the level of ambient light impinging on a pixel having a photodiode as claimed in claim 3 wherein the detecting step (b) further includes:

b.2. converting the detected current flow signal to a voltage signal; and

b.3. converting the voltage signal to a digital signal.

5. A method of determining the level of ambient light on an imaging array of pixels having photodiodes comprising:

a. resetting the pixels in the array; and

b. detecting the current flow through the photodiodes in a selected number of pixels during the resetting step to determine the ambient light level.

6. A method of determining the level of ambient light impinging on an array of active pixels having photodiodes as claimed in claim 5 wherein the resetting step (a.) includes:

a.1. applying a reverse bias voltage across the photodiodes.

7. A method of determining the level of ambient light impinging on an array of active pixels having photodiodes as claimed in claim 5 wherein the selected number of pixels are divided in one or more groups of pixels.

8. A method of detecting the level of ambient light impinging on an array of active pixels having photodiodes as claimed in claim 7 wherein the pixels in the imaging array are positioned in rows and columns.

9. A method of determining, the level of ambient light impinging on an array of active pixels having photodiodes as claimed in claim 8 wherein the pixels in each group are located in a predetermined row.

10. A method of determining the level of ambient light impinging, on an array of active pixels having photodiodes as claimed in claim 8 wherein the pixels in each group are located in predetermined column.

11. A method of determining the level of ambient light impinging on an array of active pixels having photodiodes as claimed in claim 8 wherein the pixels in each group are located in a specific pattern in the array.

12. A method of determining the level of ambient light impinging on an array of active pixels having photodiodes as claimed in claim 7 wherein detecting step (b.) includes:

b.1 detecting the current flow through a resistance in parallel to the photodiodes in each group of pixels.

13. A method of determining the level of ambient light impinging on an array of active pixels having photodiodes as claimed in claim 11 wherein detecting step (b.) further includes:

b.2. converting each detected current flow signal to a voltage signal; and

b.3 converting each of the voltage signals to a digital signal.

14. A method of determining the level of ambient light impinging on an array of active pixels having photodiodes as claimed in claim 12 wherein detecting step (b.) further includes:

b.4. combining the digital signals to provide a digital signal representative of the ambient light level.

15. A method of determining the level of ambient light on an imaging array of pixels having photodiodes comprising:

a. resetting a selected number of pixels in the array; and

b. detecting the current flow through the photodiodes in the selected number of pixels during the resetting step to determine the ambient light level.

16. A method of determining the level of ambient light impinging on an array of active pixels having photodiodes as claimed in claim 15 wherein the resetting step (a.) includes:

a.1. applying a reverse bias voltage across the photodiodes.

17. A method of determining the level of ambient light impinging on an array of active pixels having photodiodes as claimed in claim 15 wherein the selected number of pixels are divided in one or more groups of pixels.

18. A method of determining the level of ambient light impinging on an array of active pixels having photodiodes as claimed in claim 15 wherein groups of pixels are reset sequentially.

19. In an imaging array of light sensitive pixels each having a photodiode and photodiode reset means adapted to apply a predetermined reset voltage across the photodiode and one or more power rails each connected to a group of one or more of the pixels for supplying power to the pixels, apparatus for determining ambient light comprising:

Current monitoring means for measuring current flow in the photodiodes of selected pixels as the photodiodes are being reset for determining the ambient light.

20. Apparatus for measuring ambient light as claimed in claim 19 wherein the current monitoring means includes one or more current monitors each connected to at least one of the power rails for monitoring the current flow in the photodiodes connected to the power rail.

21. Apparatus for measuring ambient light as claimed in claim 20 comprising analog-to-digital converter means coupled to each of the current monitors to provide a digital signal representative of the ambient light.

22. Apparatus for measuring ambient light as claimed in claim 21 comprising resistor means couple between the current monitor and the power rail.

23. Apparatus for measuring ambient light as claimed in claim 22 wherein the current monitor comprises a current-to-voltage converter.

24. Apparatus for measuring ambient light as claimed in claim 23 wherein the current-to-voltage converter comprises an op-amp having an inverting input terminal coupled to the resistor means, a non-inverting input terminal adapted to be coupled to a reference voltage and an output terminal, the output terminal being coupled to the inverting input terminal through a further resistor means.

25. Apparatus for measuring ambient light as claimed in claim 19 wherein the imaging array and the current monitoring means are integrated on the same die.

26. Apparatus for measuring ambient light as claimed in claim 19 wherein the pixels in the imaging array are positioned in rows and columns and wherein the selected pixels are located in inner rows and columns.

27. Apparatus for measuring ambient light as claimed in claim 19 wherein the pixels in the imaging array are positioned in rows and columns and wherein the selected pixels are located in outer rows and columns.

28. Apparatus for measuring ambient light as claimed in claim 19 wherein the pixels in the imaging array are positioned in rows and columns and wherein the selected pixels are located in one or more columns.

29. Apparatus for measuring ambient light as claimed in claim 19 wherein the pixels in the imaging array are positioned in rows and columns and wherein the selected pixels are located in one or more rows.

30. Apparatus for measuring ambient light as claimed in claim 19 wherein the pixels in the imaging array are positioned in rows and columns and wherein the power rail is connected to the selected pixels arranged in a specific pattern in the array.

31. Apparatus for measuring ambient light as claimed in claim 19 wherein the pixels in the imaging array are positioned in rows and columns and wherein the power rails are connected to rows of pixels.

32. Apparatus for measuring ambient light as claimed in claim 19 wherein the pixels in the imaging array are positioned in rows and columns and wherein the power rails are connected to columns of pixels.

33. Apparatus for measuring ambient light as claimed in claim 19 wherein each pixel includes a photodiode and a reset switch.

34. Apparatus for measuring ambient light as claimed in claim 33 which further includes means for controlling the reset switches to reset individual groups of pixels sequentially.

35. Apparatus for measuring ambient light as claimed in claim 19 wherein all pixels are coupled to the same power supply.

36. Apparatus for measuring ambient light as claimed in claim 19 wherein the pixels in each group are adapted to be connected to the power supply through a separate power rail.

37. Apparatus for measuring ambient light as claimed in claim 36 wherein each separate rail is adapted to be connected to a separate power supply.

38. Apparatus for measuring ambient light as claimed in claim 36 wherein each separate rail is adapted to be connected to the power supply through a diode.

39. A system for controlling the output signal during image capture of an object by an imager having an imaging array of light sensitive pixels each having a photodiode and photodiode reset means adapted to apply a predetermined reset voltage across the photodiode and one or more power rails each connected to one or more pixels on a die comprising:

ambient light detection means located on the die adjacent to the imaging array for sensing the ambient light on the object;

means for generating an electrical signal representative of the ambient light;

means for sampling the representative electrical signal; and

means for controlling the output signal as a function of the sampled representative signal.

40. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 39 wherein the ambient light detection means comprises current monitoring means for measuring current flow in the photodiodes of selected pixels as the photodiodes are being reset for determining the ambient light.

41. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 40 wherein the current monitoring means includes one or more current monitors each connected to at least one power rail for monitoring the current flow in the photodiodes connected to the power rail.

42. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 41 wherein the electrical signal generating means includes analog-to-digital converter means coupled to each of the current monitors to provide a digital signal representative of the ambient light.

43. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 42 comprising resistor means couple between the current monitor and the power rail.

44. A system for controlling the output signal during image capture of an object by an imager having an imaging any on a die as claimed in claim 43 wherein the current monitor comprises a current-to-voltage converter.

45. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 44 wherein the current-to-voltage converter comprises an op-amp having an inverting input terminal coupled to the resistor means, a non-inverting input terminal adapted to be coupled to a reference voltage and an output terminal, the output terminal being coupled to the inverting input terminal through a further resistor means.

46. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 40 wherein the means for controlling the output signal as a function of the sampled representative signal comprises a look-up table having a variety of control signal levels as a function of light intensity and a signal driver to control the output signal.

47. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 46 comprising integrator timer means coupled to the signal driver to control the exposure time of the imaging array to the object illumination.

48. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 46 comprising illumination source control means coupled to the signal driver to control the illumination intensity.

49. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 46 comprising amplifier gain control means coupled to the signal driver to control the amplification of the output signal.

50. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 47 comprising illumination source control means coupled to the signal driver to control the illumination intensity.

51. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 50 comprising amplifier gain control means coupled to the signal driver to control the amplification of the output signal.

52. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 40 comprising a light source for illuminating the object to be imaged.

53. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 52 in which the light source comprises one or more LED'"'"'s positioned about the scanning array.

54. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 52 in which the light source comprises at least one LED positioned at one or more comers of the scanning array.