HIGH-SPEED ANALOG PHOTON COUNTER AND METHOD

• US 20120057152A1
• Filed: 09/06/2010
• Published: 03/08/2012
• Est. Priority Date: 09/06/2010
• Status: Active Grant

• Current Assignee: King Abdullah University of Science and Technology
• Original Assignee: King Abdullah University of Science and Technology
• Inventors: ELDESOUKI, MUNIR, Deen, Mohamed Jamal, Fang, Qiyin
• Granted Patent: US 8,338,773 B2
• Time in Patent Office: Days
• US Class Current: 356/226
• CPC Class Codes: G01J 1/46 using a capacitor
• CPC Class Codes: H04N 25/773 comprising photon counting circuits, e.g. single photon detection [SPD] or single photon avalanche diodes [SPAD]

Abstract

A high speed analog photon counter and method is provided. In one aspect, the method includes delivering an electric charge to a circuit of the high speed analog photon counter through a current source of the circuit. The method also includes accumulating the electric charge in a capacitor of the circuit electrically coupled to the current source. The method further includes comparing the electric charge accumulated in the capacitor of the circuit with a reference voltage through a comparator of the circuit electrically coupled to an output of the capacitor. The output of the capacitor of the circuit is coupled to an input of the comparator of the circuit, and the reference voltage is coupled to another input of the comparator of the circuit. The method furthermore includes resetting the capacitor of the circuit when the electric charge accumulated in the capacitor of the circuit matches the reference voltage.

Claims

1. A method comprising:

delivering an electric charge to a circuit through a current source of the circuit;

accumulating the electric charge in a capacitor of the circuit electrically coupled to the current source;

comparing the electric charge accumulated in the capacitor of the circuit with a reference voltage through a comparator of the circuit electrically coupled to an output of the capacitor;

resetting the capacitor of the circuit when the electric charge accumulated in the capacitor of the circuit matches the reference voltage; and

measuring an intensity of light through the circuit.

2. The method in claim 1, further comprising:

generating a digital pulse at an output of a photodiode corresponding to a photon incident on the photodiode, wherein the output of the photodiode is coupled to an input of the current source;

delivering an amount of the electric charge proportional to a pulse width of the digital pulse;

increasing an output voltage of the capacitor of the circuit proportional to each of the electric charge accumulated in the capacitor, wherein the increase in the output voltage of the capacitor to correspond to the photon incident on the photodiode; and

accumulating the electric charge until the output voltage of the capacitor of the circuit is to match the reference voltage at the comparator of the circuit.

3. The method of claim 1, further comprising:

generating a reset pulse at an output of the comparator of the circuit when the output of the capacitor of the circuit matches the reference voltage at the comparator of the circuit; and

resetting the capacitor through a first reset transistor of the circuit electrically coupled to the output of the comparator of the circuit.

clearing the circuit through a second reset transistor, wherein the second reset transistor to receive a signal external to the circuit to clear the circuit.

4. The method of claim 3:

wherein the output of the capacitor of the circuit is coupled to an input of the comparator of the circuit, and

wherein the reference voltage is coupled to another input of the comparator of the circuit.

5. The method of claim 1:

wherein the reference voltage to correspond to a threshold number of counts of photons incident on a photodiode, and

wherein the reference voltage is determined based on an application of a measurement device.

6. The method of claim 3, wherein the accumulation and comparison operation to reduce a number of transistors used to implement the circuit and the comparator to approximately 20 transistors.

7. The method of claim 6, further comprising:

increasing a fill factor of a pixel through reducing the number of transistors to implement the circuit and the comparator of the circuit, wherein increasing the fill factor of the pixel to increase a resolution of an output of a measurement device.

8. The method of claim 1,

wherein the circuit and a photodiode is implemented inside a pixel, and

wherein the circuit to count a number of photons incident on the photodiode and determine an intensity of a light.

9. The method of claim 8, further comprising:

increasing a speed of operation of a measurement device through implementing the circuit inside the pixel.

10. The method of claim 6, wherein a maximum number of incident photons countable through the circuit is independent of the number of transistors in the circuit.

11. The method of claim 10, further comprising:

serially coupling an n-number of the circuit to increment the maximum number of incident photons countable through the circuit; and

activating an nth circuit of the n-number of the circuit through the output of an (n-1)^th circuit of the n-number of the circuit, wherein n is an integer value greater than 1.

12. The method in claim 11, wherein the capacitor of the n^th circuit is electrically coupled to the output of the comparator of the (n-1)^th circuit through an nth current source, wherein the capacitor of a first circuit is electrically coupled to the output of a photodiode through the current source.

13. The method claim 11, further comprising:

determining the n-number through a threshold fill factor of a pixel, wherein a fill factor of the pixel is an area occupied by an active area of a photodiode as compared to a combined layout area of the photodiode, the circuit, the n-number of the circuit, the comparator and the current source in the pixel.

14. The method of claim 11:

wherein the increment in a maximum number of incident photons that the circuit can count to increase a dynamic range of a measurement device, and

wherein the serial coupling of the n-number of the circuit to reduce the sensitivity requirements of the comparator through limiting the maximum count of each stage to have a large count step size.

15. A method comprising:

accumulating an electric charge in a capacitor of a circuit electrically coupled to a current source of the circuit;

comparing the electric charge accumulated in the capacitor of the circuit with a reference voltage through a comparator of the circuit electrically coupled to an output of the capacitor; and

increasing a speed of operation of a measurement device through implementing the circuit inside a pixel.

16. The method of claim 15 further comprising:

delivering the electric charge to the circuit through the current source;

resetting the capacitor of the circuit when the electric charge accumulated in the capacitor of the circuit matches the reference voltage; and

measuring an intensity of light through the circuit and the comparator of the circuit.

17. The method in claim 15, further comprising:

generating a digital pulse at an output of a photodiode corresponding to a photon incident on the photodiode, wherein the output of the photodiode is coupled to an input of the current source;

delivering an amount of the electric charge proportional to a pulse width of the digital pulse; and

increasing an output voltage of the capacitor of the circuit proportional to each of the electric charge accumulated in the capacitor, wherein the increase in the output voltage of the capacitor to correspond to the photon incident on the photodiode.

18. The method of claim 15, further comprising:

accumulating the electric charge until the output voltage of the capacitor of the circuit to match the reference voltage at the comparator of the circuit.

generating a reset pulse at an output of the comparator of the circuit when the output of the capacitor of the circuit matches the reference voltage at the comparator of the circuit;

resetting the capacitor through a first reset transistor of the circuit electrically coupled to the output of the comparator of the circuit; and

clearing the circuit through a second reset transistor, wherein the second reset transistor to receive a signal external to the circuit to clear the circuit.

19. An image sensor device comprising:

a pixel circuit; and

an intensity measurement circuit implemented in the pixel circuit;

to measure an intensity of light and to increase a speed of operation of the image sensor device.

20. The image sensor device of claim 19, wherein the intensity measurement circuit further comprising:

a first circuit to deliver an electric charge to the intensity measurement circuit through a current source;

a second circuit to accumulate the electric charge in a capacitor of the intensity measurement circuit electrically coupled to the current source; and

a third circuit to compare the electric charge accumulated in the capacitor of the intensity measurement circuit with a reference voltage through a comparator of the intensity measurement circuit electrically coupled to an output of the capacitor.

21. The image sensor device of claim 20:

wherein the capacitor of the intensity measurement circuit to reset when the electric charge accumulated in the capacitor of the intensity measurement circuit matches the reference voltage,

wherein the comparator to generate a reset pulse at an output of the comparator of the intensity measurement circuit when the output of the capacitor of the intensity measurement circuit matches the reference voltage at the comparator of the intensity measurement circuit,

wherein the capacitor of the intensity measurement device to reset through a first reset transistor of the intensity measurement circuit electrically coupled to the output of the comparator of the intensity measurement circuit,

wherein the intensity measurement circuit to reset through a second reset transistor, and

wherein the second reset transistor to receive a signal external to the circuit to clear the circuit

22. The image sensor device of claim 19 further comprising:

a photodiode external to the intensity measurement circuit to;

generate a digital pulse at the output of the photodiode, wherein the output of the photodiode is electrically coupled to an input of the current source of the intensity measurement circuit, and

deliver an amount of the electric charge proportional to a pulse width of the digital pulse to the intensity measurement circuit through the current source of the intensity measurement circuit.

23. The image sensor device of claim 22:

wherein an output voltage of the capacitor of the intensity measurement circuit to increase directly proportional to each of the electric charge accumulated in the capacitor, wherein the increase in the output voltage of the capacitor to correspond to the number of photons incident on the photodiode, and

wherein the photodiode is implemented inside the pixel circuit.

24. The image sensor device of claim 19, wherein the intensity measurement circuit to detect photons from n-number of photodiodes through coupling additional current sources between each of the n-number of photodiodes and the intensity measurement circuit when the image sensor device includes n-number of photodiodes, such that the input of each current source is coupled with each photodiode and an output of each current source is coupled with the intensity measurement circuit.

25. The image sensor device of claim 19:

wherein the current source is a voltage controlled current source;

wherein the intensity measurement circuit to accumulate the electric charge until an output voltage of the capacitor of the intensity measurement circuit matches the reference voltage at the comparator of the intensity measurement circuit, and

wherein the reference voltage to correspond to a threshold number of counts of photons incident on a photodiode