LIDAR SENSOR HISTOGRAM COMPUTATION

1 . A method, comprising:

actuating a laser diode to emit a first series of laser pulses in a first frequency;

enabling ap single-photon-avalanche diode (SPAD) in a pixel 104 of a focal-plane array to detect a photon during a first series of enable times defined by a first series of enable pulses in a second frequency greater than the first frequency; and

updating a histogram memory based on a photon detected during the first series of enable times.

2 . The method of claim 1 , further comprising:

actuating the laser diode to emit a second series of laser pulses in the first frequency;

at a first time offset, enabling the SPAD to detect a photon during a second series of enable times defined by a second series of enable pulses in the second frequency; and

updating the histogram memory based on a photon detected during the second series of enable times.

3 . The method of claim 2 , further comprising:

actuating the laser diode to emit a third series of laser pulses in the first frequency; and

at a second time offset, enabling the SPAD to detect a photon during a third series of enable times defined by a third series of enable pulses in the second frequency.

4 . The method of claim 3 , wherein the second series of enable pulses and the third series of enable pulses are non-overlapping.

5 . The method of claim 2 , further comprising:

determining a plurality of time offsets; and

at each of the plurality of time offsets, enabling the SPAD to detect a photon during a second series of enable times defined by a second series of enable pulses in the second frequency, wherein the plurality of second series of enable pulses covers a clock period of the first series of laser pulses.

6 . The method of claim 2 , further comprising updating a respective bin of the first histogram based on a detected photon, wherein a number of bins is defined based on the first and second frequencies.

7 . The method of claim 6 , further comprising

actuating the laser diode to emit a third series of laser pulses in the first frequency;

at the first time offset, enabling the SPAD to detect a photon during a third series of enable times defined by a third series of enable pulses in the second frequency; and

updating the first histogram memory based on a photon detected during the third series of enable times.

8 . The method of claim 2 , further comprising detecting a distance to an object based on the second histogram.

9 . The method of claim 8 , further comprising:

applying a matched filter to second histogram data;

detecting the distance to the object based on an identified maximum of the histogram data.

10 . A control system of a lidar unit comprising instructions executable to:

actuate a laser diode to emit a first series of laser pulses in a first frequency;

enable ap single-photon-avalanche diode (SPAD) in a pixel 104 of a focal-plane array to detect a photon during a first series of enable times defined by a first series of enable pulses in a second frequency greater than the first frequency; and

update a histogram memory based on a photon detected during the first series of enable times.

11 . The control system of claim 10 , wherein the instructions further include instructions to:

actuate the laser diode to emit a second series of laser pulses in the first frequency;

at a first time offset, enable the SPAD to detect a photon during a second series of enable times defined by a second series of enable pulses in the second frequency; and

update the histogram memory based on a photon detected during the second series of enable times.

12 . The control system of claim 11 , wherein the instructions further include instructions to:

actuate the laser diode to emit a third series of laser pulses in the first frequency; and

at a second time offset, enable the SPAD to detect a photon during a third series of enable times defined by a third series of enable pulses in the second frequency.

13 . The control system of claim 12 , wherein the second series of enable pulses and the third series of enable pulses are non-overlapping.

14 . The control system of claim 11 , wherein the instructions further include instructions to:

determine a plurality of time offsets; and

at each of the plurality of time offsets, enable the SPAD to detect a photon during a second series of enable times defined by a second series of enable pulses in the second frequency, wherein the plurality of second series of enable pulses covers a clock period of the first series of laser pulses.

15 . The control system of claim 11 , wherein the instructions further include instructions to update a respective bin of the histogram based on a detected photon, wherein a number of bins is defined based on the first and second frequencies.

16 . The control system of claim 15 , wherein the instructions further include instructions to:

actuate the laser diode to emit a third series of laser pulses in the first frequency;

at the first time offset, enable the SPAD to detect a photon during a third series of enable times defined by a third series of enable pulses in the second frequency; and

update the histogram memory based on a photon detected during the third series of enable times.

17 . The control system of claim 10 , wherein the instructions further include instructions to detect a distance to an object based on the updated histogram.

18 . The control system of claim 17 , wherein the instructions further include instructions to:

apply a matched filter to histogram data;

detect the distance to the object based on an identified maximum of the histogram data.

19 . A pixel circuit, comprising:

one or more SPAD diodes;

one or more SPAD diode quench circuits, configured to quench said SPAD diodes;

a SPAD control circuit configured to respond to a sequence of timing pulses and further configured to create a sequence of apertures relating to the sequence of timing pulses wherein a SPAD avalanche event can be recorded;

a histogram memory circuit configured to record SPAD avalanche events as histogram bin counts; and

a readout circuit configured to be coupled to readout circuits of other pixels, allowing histogram data to be transferred out of the pixel.