Depth map sensor based on dToF and iToF

Patent metadata

Field	Value
Publication number	US-11209310-B2
Application number	US-202017006436-A
Country	US
Kind code	B2
Filing date	Aug 28, 2020
Priority date	Aug 30, 2019
Publication date	Dec 28, 2021
Grant date	Dec 28, 2021

Abstract

The present disclosure relates to a depth map sensor including a light source for transmitting light pulses into an image scene; an array of pixel circuits, where each pixel circuit has a photodetector and three asynchronous counters; and a control circuit to control each of a plurality of groups of the pixel circuits of the array to generate a histogram of detection events by accumulating events during eight distinct time intervals between consecutive light pulses transmitted by the light source, such that the histogram comprises eight or more histogram bins.

First claim

What is claimed is:

1. A depth map sensor comprising:
a light source for transmitting light pulses into an image scene;
an array of pixel circuits, each pixel circuit of the array of pixel circuits comprising a photodetector and asynchronous counters that comprises a first, a second, and a third asynchronous counter; and
a control circuit configured to control each of a plurality of groups of the array of the pixel circuits to generate a histogram of detection events by accumulating events during eight distinct time intervals between consecutive light pulses transmitted by the light source, wherein the histogram comprises eight or more histogram bins, wherein the number of histogram bins is greater than the number of asynchronous counters of each pixel circuit.

2. The depth map sensor of claim 1 , wherein the control circuit is configured to control one or more first ones of the array of pixel circuits to accumulate in its asynchronous counters, detection events in three of the eight distinct time intervals, and to control one or more second ones of the array of pixel circuits to accumulate in its three asynchronous counters, detection events in another three of the eight distinct time intervals.

3. The depth map sensor of claim 2 , wherein the control circuit is configured to control, during a first cycle between the consecutive light pulses, the first ones of the array of pixel circuits to accumulate the events in the three distinct time intervals and the second ones of the array of pixel circuits to accumulate the events in the another three distinct time intervals.

4. The depth map sensor of claim 2 , wherein the control circuit is configured to control, during a first cycle between two consecutive light pulses, the first ones of the array of pixel circuits to accumulate the events in the three distinct time intervals, and during a second cycle between a further two consecutive light pulses, the second ones of the array of pixel circuits to accumulate the events in the another three distinct time intervals.

5. The depth map sensor of claim 4 , wherein during the first cycle, the control circuit is configured to control only pixel circuits to accumulate the events in the three distinct time intervals, and during the second cycle, the control circuit is configured to control only pixel circuits to accumulate the events in the another three distinct time intervals.

6. The depth map sensor of claim 1 , wherein the light source is a laser light source, such as a vertical cavity surface-emitting laser.

7. The depth map sensor of claim 1 , wherein the photodetectors are single photon avalanche diodes.

8. A method of generating a histogram using a depth map sensor, the method comprising:
transmitting, from a light source, light pulses into an image scene; and
controlling each of a plurality of groups of pixel circuits of an array of pixel circuits to generate a histogram of detection events by accumulating events during eight distinct time intervals between consecutive light pulses transmitted by the light source, wherein the histogram comprises eight or more histogram bins, wherein each pixel circuit of the array has a photodetector and asynchronous counters that comprises a first, a second, and a third asynchronous counter, and wherein the number of histogram bins is greater than the number of asynchronous counters of each pixel circuit of the array.

9. The method of claim 8 , further comprising controlling one or more first ones of the pixel circuits to accumulate in its three asynchronous counters detection events in three of the eight distinct time intervals, and controlling one or more second ones of the pixel circuits to accumulate in its three asynchronous counters detection events in another three of the eight distinct time intervals.

10. The method of claim 9 , further comprising controlling, during a first cycle between the consecutive light pulses, the first ones of the array of pixel circuits to accumulate the events in the three distinct time intervals and the second ones of the array of pixel circuits to accumulate the events in the another three distinct time intervals.

11. The method of claim 9 , further comprising controlling, during a first cycle between two consecutive light pulses, the first ones of the array of pixel circuits to accumulate the events in the three distinct time intervals, and during a second cycle between a further two consecutive light pulses, the second ones of the array of pixel circuits to accumulate the events in the another three distinct time intervals.

12. The method of claim 11 , further comprising controlling during the first cycle only pixel circuits to accumulate the events in the three distinct time intervals, and during the second cycle, only pixel circuits to accumulate the events in the another three distinct time intervals.

13. The method of claim 8 , further comprising:
generating a depth map by generating a first frame of macro pixels each comprising a first histogram based on a first duration of eight distinct time intervals, and generating a second frame of macro pixels each comprising a second histogram based on a second duration of eight distinct time intervals, wherein the first and second durations are not equal, wherein each of the first histogram and the second histogram is generated by the transmitting of the light pulses and the controlling, wherein each of the first and the second histograms comprise eight or more histogram bins.

14. The method of claim 8 , further comprising:
generating a depth map by generating a first frame of macro pixels each comprising the histogram; and
generating a second frame based on an indirect time of flight, iToF, operation of each pixel circuit of the array.

15. A method of correcting cross-talk in a depth map sensor, the method comprising:
generating, a histogram for a plurality of zones of an array of pixel circuits, the generating comprising
transmitting, from a light source, light pulses into an image scene, and
controlling each of a plurality of groups of pixel circuits of an array of pixel circuits to generate a histogram of detection events by accumulating events during eight distinct time intervals between consecutive light pulses transmitted by the light source, wherein the histogram comprises eight or more histogram bins, wherein each pixel circuit of the array has a photodetector and asynchronous counters that comprises a first, a second, and a third asynchronous counter, and wherein the number of histogram bins is greater than the number of asynchronous counters of each pixel circuit of the array;

generating, based on the histogram for the plurality of zones, cross-talk grid points representing cross-talk present in each of the plurality of zones; and
correcting a depth map by subtracting, from one or more histogram bins generated during an indirect time of flight, iToF, operation, cross-talk estimations generated based on the cross-talk grid points.

16. The method of claim 15 , further comprising controlling one or more first ones of the pixel circuits to accumulate in its three asynchronous counters detection events in three of the eight distinct time intervals, and controlling one or more second ones of the pixel circuits to accumulate in its three asynchronous counters detection events in another three of the eight distinct time intervals.

17. The method of claim 16 , further comprising controlling, during a first cycle between the consecutive light pulses, the first ones of the array of pixel circuits to accumulate the events in the three distinct time intervals an

Assignees

• St Microelectronics Grenoble 2

Inventors

• Mellot Pascal
• Plaza Laurent
• Chinal Jeannie

Classifications

• G01S7/4863 Primary

  Detector arrays, e.g. charge-transfer gates · CPC title

• G01J1/44 Primary

  Electric circuits {(for command of an exposure part G03B7/02)} · CPC title

• G01S7/4876

  by removing unwanted signals (G01S7/495 takes precedence) · CPC title

• G01S7/497

  Means for monitoring or calibrating · CPC title

• G01J2001/442

  Single-photon detection or photon counting · CPC title