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Ambient light detection technique for an imaging array

Imported: 23 Feb '17 | Published: 22 Oct '02

John Scott-Thomas, Alex Roustaei, Paul Vulpoiu

USPTO - Utility Patents

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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanying drawings, wherein:

FIG. 1 schematically illustrates a voltage supply coupled to an array of light sensitive pixels as well as a pixel circuit that may be used in the present invention;

FIG. 2

a illustrates a block diagram of the present invention;

FIG. 2

b illustrates a block diagram of the present invention having a single current monitor;

FIG. 2

c illustrates a block diagram of the present invention having multiple voltage supplies;

FIG. 2

d illustrates a block diagram of the present invention having isolated power rails;

FIG. 3

a illustrates a block diagram of the ambient light detector;

FIG. 3

b illustrates a circuit that may be used as a current monitor in the ambient light detector;

FIGS. 4

a,

4

b,

4

c and

4

d illustrate various possible layouts for the imaging array for the detection of ambient light in specific areas of an array.

FIG. 5 illustrates a block diagram of an exposure control system with which the ambient light detector in accordance with the present invention may be used; and

FIG. 6 illustrates the face of an image scanner.

Claims

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

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

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:

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:

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

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:

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:

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:

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:

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

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:

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:

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:

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.