CMOS READOUT ARCHITECTURE AND METHOD FOR PHOTON-COUNTING ARRAYS

• US 20110235771A1
• Filed: 03/23/2010
• Published: 09/29/2011
• Est. Priority Date: 03/23/2010
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Renzi, Matthew J., Aull, Brian F., Reich, Robert K., Schuette, Daniel R.
• Granted Patent: US 8,426,797 B2
• Time in Patent Office: Days
• US Class Current: 377/19
• CPC Class Codes: H04N 25/57 Control of the dynamic range
• CPC Class Codes: H04N 25/772 comprising A/D, V/T, V/F, I/T or I/F converters

Abstract

Embodiments of the present invention include complementary metal-oxide-semiconductor (CMOS) readout architectures for photon-counting arrays with a photon-counting detector, a digital counter, and an overflow bit in each of the sensing elements in the array. Typically, the photon-counting detector is a Geiger-mode avalanche photodiode (APD) that emits brief pulses every time it detects a photon. The pulse increments the digital counters, which, in turn, sets the overflow bit once it reaches a given count. A rolling readout system operably coupled to each sensing element polls the overflow bit, and, if the overflow bit is high, initiates a data transfer from the overflow bit to a frame store. Compared to other photo-counting imagers, photon-counting imagers with counters and overflow bits operate with decreased transfer bandwidth, high dynamic range, and fine spatial resolution.

Claims

1. An apparatus for detecting and counting photons, comprising:

sensing elements, each sensing element including;

a photon-counting detector;

a digital counter operably coupled to the photon-counting detector and responsive to signals from the photon-counting detector;

an overflow bit operably coupled to the digital counter and responsive to the digital counter; and

a rolling readout system operably coupled to each sensing element and configured to poll the overflow bit.

2. An apparatus as in claim 1, wherein the photon-counting detector is a Geiger-mode avalanche photodiode.

3. An apparatus as in claim 2, wherein each sensing element includes a reset circuit configured to charge the Geiger-mode avalanche photodiode between arrival of successive photons.

4. An apparatus as in claim 1, wherein the digital counter includes at least one of a binary counter, a ripple counter, and a pseudorandom counter.

5. An apparatus as in claim 1, wherein the apparatus transfers data from the overflow bit if the overflow bit is high when polled.

6. An apparatus as in claim 1, wherein the apparatus does not transfer data from the overflow bit if the overflow bit is low when polled.

7. An apparatus as in claim 1, wherein the overflow bit is a bit in the digital counter.

8. An apparatus as in claim 7, wherein the overflow bit is a most-significant bit in the digital counter.

9. An apparatus as in claim 7, further including:

a selector operably coupled to the digital counter and configured to select the overflow bit from among bits in the digital counter.

10. An apparatus as in claim 1, further including:

logic coupled to the digital counter and the overflow bit, the logic configured to set the overflow bit based on a count stored in the digital counter.

11. An apparatus as in claim 1, wherein the overflow bit is configured to be polled periodically at a polling period.

12. An apparatus as in claim 11, wherein the polling period is longer than a time between detection of successive photons.

13. An apparatus as claim 11, further including:

a residue readout system operably coupled to the digital counter and configured to read out the entire digital counter periodically at an interrogation period longer than the polling period.

14. An apparatus as in claim 1, wherein the rolling readout system is configured to control when the overflow bit is polled.

15. An apparatus as in claim 1, further including:

a sensing line operably coupled to at least one sensing element and configured to transfer data from the sensing element.

16. An apparatus as in claim 1, further including:

a frame-store accumulator operably coupled to the overflow bit and configured to store data from the overflow bit.

17. An apparatus as in claim 1, in combination with an external processor or external memory operably coupled to the overflow bit and configured to store or process data from the overflow bit.

18. A detector array as in claim 1 in combination with an imaging system.

19. A method of detecting and counting photons, comprising:

detecting photons at a particular sensing element in an array of sensing elements;

incrementing a digital counter in the particular sensing element in response to detection of each photon by the sensing element;

setting an overflow bit in the particular sensing element responsive to the digital counter'"'"'s indicating that a certain number of photons has been counted; and

polling the overflow bit to yield an indication that the certain number of photons has been counted.

20. A method as in claim 19, wherein detecting photons includes detecting photons with a Geiger-mode avalanche photodiode.

21. A method as in claim 20, further including:

resetting the Geiger-mode avalanche photodiode after detection of a photon.

22. A method as in claim 19, wherein the digital counter includes at least one of a binary counter, a ripple counter, and a pseudorandom counter.

23. A method as in claim 19, further including:

transferring data from the overflow bit if the overflow bit is high when polled.

24. A method as in claim 19, wherein the overflow bit is a bit in the digital counter.

25. A method as in claim 24, wherein the overflow bit is a most-significant bit in the digital counter.

26. A method as in claim 19, further including:

selecting the overflow bit from among bits in the digital counter.

27. A method as in claim 26, wherein setting the overflow bit includes incrementing the overflow bit based on data stored in the digital counter.

28. A method as in claim 19, wherein polling the overflow bit occurs periodically at a polling period.

29. A method as in claim 19, wherein polling the overflow bit occurs less frequently than detecting photons.

30. A method as claim 19, further including:

interrogating the digital counter less frequently than the polling of the overflow bit.

31. A method as in claim 19, further including:

controlling when the overflow bit is polled.

32. A method as in claim 19, further including:

transferring data from the overflow bit to a frame-store accumulator.

33. A method as in claim 19, further including:

transferring data from the overflow bit to an off-chip processor or off-chip memory; and

processing the overflow bit with the off-chip processor or storing the overflow bit with the off-chip memory.

34. A method as in claim 19, further including:

forming an image based on indications of the number of detected photons from at least one of the digital counters and the overflow bits.

35. A sensing element, comprising:

a photon-counting detector;

a digital counter operably coupled to the photon-counting detector and responsive to signals from the photon-counting detector; and

an overflow bit operably coupled to the digital counter and responsive to the digital counter.