# US 12,192,656 B2 · Low-power image sensor system with single-photon avalanche diode photodetectors

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- Number: US 12,192,656 B2
- Document ID: US12192656B2
- Status: Granted
- Kind: B2
- Application number: 17/631,303
- Filed: 2019-08-01
- Published: 2022-08-18
- Granted: 2025-01-07
- Earliest claimed: 2019-08-01
- Assignees: Ecole Polytechnique Federale de Lausanne
- Applicants: Ecole Polytechnique Federale De Lausanne (Epfl)
- Inventors: Ivan Michel Antolovic; Claudio Bruschini; Edoardo Charbon
- Web page: https://patentgrep.com/patent/US12192656B2

## CPC

- G01T 1/171: {Compensation of dead-time counting losses}
- H04N 25/77: Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components
- H04N 25/00: Circuitry of solid-state image sensors [SSIS]; Control thereof
- H04N 25/571: involving a non-linear response
- H04N 25/773: comprising photon counting circuits, e.g. single photon detection [SPD] or single photon avalanche diodes [SPAD]
- H10F 30/225: the potential barrier working in avalanche mode, e.g. avalanche photodiodes
- H10F 39/18: Complementary metal-oxide-semiconductor [CMOS] image sensors; Photodiode array image sensors
- G01T: MEASUREMENT OF NUCLEAR OR X-RADIATION (radiation analysis of materials, mass spectrometry G01N23/00; tubes for determining the presence, intensity, density or energy of radiation or particles H01J47/00)
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION
- H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION

## Abstract

The invention relates to an image sensor comprising a photodetector array including neighboring photodetector elements, each photodetector element comprising: —a photodetector cell having a photodiode and a reset unit; —a cell control unit coupled with the photodetector cell and configured to reset the photodiode by means of the reset unit; wherein the cell control unit is configured to asynchronously effect resetting of the photodiode after a given dead time after detection of a photon.

## Claims

### Claim 1

An image sensor comprising a photodetector array including neighboring photodetector elements, each photodetector element comprising:
a photodetector cell with a photodiode and a reset unit;
a cell control unit coupled with the photodetector cell and configured to reset the photodiode by means of the reset unit;
wherein the cell control unit is configured to asynchronously effect resetting of the photodiode after a given dead time after detection of a photon,
wherein a post-processing unit is configured to retrieve counter values of all photodetector elements,
wherein the post-processing unit is configured to linearize counter values of all photodetector elements independently or globally.

### Claim 2 (depends on 1)

The image sensor according to claim 1, wherein the photodiode of each photodetector element comprises an avalanche photodiode, such as a single-photon avalanche diode.

### Claim 3 (depends on 2)

The image sensor according to claim 2, wherein the resetting of the avalanche photodiode is performed by recharging an electrical field in the photodiode.

### Claim 4 (depends on 1)

The image sensor according to claim 1, wherein the cell control unit is configured to asynchronously effect resetting of the photodiode exactly with a delay of the given dead time after detection of the photon.

### Claim 5 (depends on 1)

The image sensor according to claim 1, wherein a counter unit is configured to count photon detection events in the photodiode during a given frame time.

### Claim 6 (depends on 5)

The image sensor according to claim 5, wherein the bit width U of the counter unit is set depending on frame time so that the frame time corresponds to at least the product (2U−1) and the dead time.

### Claim 7 (depends on 5)

The image sensor according to claim 5, wherein the frame time is set so that the dark counts (DC) which correspond to the product of the dark count rate and the frame time is √{square root over (DC)}<1, as to enable photon counting.

### Claim 8 (depends on 1)

The image sensor according to claim 1, having global time-gating at the pixel level, selectively enabling photon detection counting.

### Claim 9 (depends on 1)

The image sensor according to claim 1, wherein the dead time is set so that the ratio of the recorded counts in the pixel counter versus the number of photon detection events corresponding to the light intensity is lower than 0.9 preferably lower than 0.8 for more than 100 photon detection events, particularly for more than 200 photon detection events, corresponding to the light intensity.

### Claim 10 (depends on 1)

The image sensor according to claim 1, wherein the post-processing unit is configured to decompress, particularly linearize, counter values of all photodetector elements independently or globally.

### Claim 11 (depends on 1)

The image sensor according to claim 1, wherein the cell control unit of each photodetector element has an individually set dead time.

### Claim 12 (depends on 1)

The image sensor according to claim 1, wherein the cell control unit of each photodetector element is configured to variate the dead time depending on the light intensity.

### Claim 13 (depends on 1)

The image sensor according to claim 1, wherein the size of the counter unit is between 8 and 14 bits.

### Claim 14 (depends on 1)

The image sensor according to claim 1, wherein the dead time is between 0.5 to 60 μs, preferably between 2 and 20 μs.

### Claim 15 (depends on 1)

The image sensor according to claim 1, wherein the counter unit has two counters which are configured to allow an intermitting operation of counting and reading out.

### Claim 16 (depends on 1)

The image sensor according to claim 1, wherein the counter unit has one counter and a latched memory which are configured to copy the counter value into the latched memory after a frame time while continuously counting photon detection events using the counter.

### Claim 17 (depends on 1)

The image sensor according to claim 1, wherein the resistance of the photodiode is set to between 500 Ω and 1500Ω, preferable to between 800 and 1200 Ω.

### Claim 18 (depends on 17)

The image sensor according to claim 17, wherein a serial resistance is coupled with the photodiode to increase the resistance of the photodiode to between 500Ω and 1500Ω, preferable to between 800 and 1200 Ω.

### Claim 19

A method for operating an image sensor comprising a photodetector array including neighboring photodetector elements, wherein each photodetector element has a photodiode and a reset unit, wherein the photodiode is asynchronously reset after a given dead time after detection of a photon;
wherein a post-processing unit retrieves counter values of all photodetector elements and linearizes counter values of all photodetector elements independently or globally.

### Claim 20 (depends on 19)

The method according to claim 19, wherein a plurality of photon detection events in each photodetector element are separately counted with a given frame time.