Higher dynamic range image sensor with signal integration

• US 7,202,463 B1
• Filed: 09/16/2005
• Issued: 04/10/2007
• Est. Priority Date: 09/16/2005
• Status: Expired due to Fees

• Current Assignee: Adobe Systems Incorporated (Adobe Inc.), Agilent Technologies, Inc.
• Original Assignee: Adobe Systems Incorporated (Adobe Inc.)
• Inventors: Cox, Christopher B.
• Primary Examiner(s): Allen; Stephone B.
• Assistant Examiner(s): MONBLEAU, DAVIENNE N
• Application Number:
  US11/229,330
• Time in Patent Office: 571 Days
• Field of Search: 250/208.1, 250/214.R, 250/214.DC, 250/214.SW, 327/514, 348/296, 348/297, 348/308, 348/310
• US Class Current: 250/214.00R
• CPC Class Codes: G01J 1/44 Electric circuits for command of an exposure part G03B7/02
• CPC Class Codes: G01J 1/46 using a capacitor
• CPC Class Codes: G01J 2001/4406 Plural ranges in circuit, e.g. switchable ranges; Adjusting sensitivity selecting gain values
• CPC Class Codes: H04N 25/00 Circuitry of solid-state image sensors [SSIS]; Control thereof
• CPC Class Codes: H04N 25/772 comprising A/D, V/T, V/F, I/T or I/F converters

Abstract

Briefly, in accordance with one embodiment of the invention, a higher dynamic range image sensor may be implemented by comparing a voltage across the sensor to a threshold voltage during image capture. At the threshold voltage, a count may be registered and the image sensor may be reset for continued image capture until an exposure is complete. A final image signal may be obtained by multiplying the threshold voltage by the number of counts registered and adding the final image sensor voltage.

Claims

1. An apparatus, comprising:

a comparator;

an image sensor coupled to an input of said comparator, wherein the output of said comparator is triggered in the event a voltage of said image sensor meets and/or exceeds a threshold voltage;

a counting circuit coupled to an output of said comparator, said counting circuit comprising a capacitor to be charged in proportion to a number of times the comparator is triggered by said image sensor, wherein said counting circuit comprises a lower range counting circuit and a higher range counting circuit;

wherein an output signal, representative at least in part of a light signal detected by said image sensor, is based at least in part on a voltage of the capacitor and a charge on the image sensor.

2. An apparatus as claimed in claim 1, wherein said image sensor comprises a photodiode.

3. An apparatus as claimed in claim 1, further comprising a switch to reset said image sensor in the event the comparator is triggered.

4. An apparatus as claimed in claim 1, further comprising a pulse shaper coupled to the output of said comparator to shape the output of the comparator for said counting circuit.

5. An apparatus as claimed in claim 1, further comprising a switch coupled in series with said image sensor and a capacitor coupled in parallel with said image sensor to function as a shutter control.

6. An apparatus as claimed in claim 1, wherein one of said lower range counting circuit or said higher range counting circuit comprises a higher precision counting circuit and another of said lower range counting circuit or said higher range counting circuit comprises a lower precision counting circuit.

7. An apparatus as claimed in claim 1, wherein said lower range counting circuit comprises a higher precision circuit, or said higher range counting circuit comprises a lower precision circuit, or combinations thereof.

8. An apparatus as claimed in claim 1, further comprising a second comparator having an input coupled to said lower range counting circuit, and said higher range counting circuit coupled to an output of said second comparator.

9. A method, comprising:

comparing a voltage of an image sensor to a threshold voltage;

registering a count when the voltage of the image sensor meets and/or exceeds a threshold voltage, said registering comprising counting over a lower range of counts with a first counting circuit and counting over a higher range of counts with a second counting circuit;

resetting the image sensor when a count is registered;

continuing with said comparing, said registering, and said resetting until an exposure is complete; and

providing an output voltage representing a number of counts, and a voltage of the image sensor.

10. A method as claimed in claim 9, further comprising performing pulse shaping of a signal that causes said registering to occur.

11. A method as claimed in claim 9, further comprising executing said comparing, said registering, said resetting, said continuing and said providing while a shutter switch is closed.

12. A method as claimed in claim 9, said registering comprising counting at a lower precision with the second counting circuit and counting at a higher precision with the first counting circuit.

13. An apparatus, comprising:

means for comparing a first input with a second input;

means for providing a voltage in response to a light signal, said voltage providing means being coupled to the first input of said comparing means, wherein an output of said comparing means is triggered in the event a voltage of said voltage providing means meets and/or exceeds a threshold voltage applied to the second input of said comparing means; and

a means for accumulating a charge, said charge accumulating means being coupled to the output of said comparing means, wherein said accumulating means accumulates a charge proportional to a number of times said comparing means is triggered by said voltage providing means, wherein said accumulating means comprises a lower range accumulating means and a higher range accumulating means;

wherein an output signal, representative at least in part of a light signal detected by said voltage providing means, is based at least in part on a charge accumulated by said accumulating means and a voltage of said voltage providing means.

14. An apparatus as claimed in claim 13, wherein said voltage providing means comprises a photodiode.

15. An apparatus as claimed in claim 13, further comprising means for controlling a current path to reset said voltage providing means in the event said comparing means is triggered.

16. An apparatus as claimed in claim 13, further comprising means for shaping a pulse, said pulse shaping means being coupled to the output of said comparing means, said pulse shaping means to shape the output of the comparing means for said accumulating means.

17. An apparatus as claimed in claim 13, further comprising means to selectively activate said voltage providing means.

18. An apparatus as claimed in claim 13, wherein one of said lower range accumulating means or said higher range accumulating means comprises a higher precision accumulating means and another of said lower range accumulating means or said higher range accumulating means comprises a lower precision accumulating means.

19. An apparatus as claimed in claim 13, wherein said lower range accumulating means comprises a lower range, higher precision counting circuit and said higher range accumulating means comprises a higher range, lower precision counting circuit.

20. An apparatus as claimed in claim 13, further comprising a second comparing means having an input coupled to said lower range accumulating means, and said higher range accumulating means coupled to an output of said second comparing means.

21. An apparatus, comprising:

means for comparing a voltage of an image sensor to a threshold voltage;

means for registering a count when the voltage of the image sensor meets and/or exceeds a threshold voltage, said registering means comprising first counting means for counting over a lower range of counts and second means for counting over a higher range of counts;

means for resetting the image sensor when a count is registered; and

means for providing an output voltage representing a number of counts, and a voltage of the image sensor.

22. An apparatus as claimed in claim 21, further comprising means for pulse shaping of a signal that activates said registering means.

23. An apparatus as claimed in claim 21, further comprising means for selectively activating said comparing means.

24. An apparatus as claimed in claim 21, said second means comprising means for counting at a lower precision and said first means comprising second counting means for counting at a higher precision.