Quantum film direct time of flight sensor circuit for low cost short wave infrared operation

Patent metadata

Field	Value
Publication number	US-12487342-B2
Application number	US-202217746111-A
Country	US
Kind code	B2
Filing date	May 17, 2022
Priority date	May 17, 2022
Publication date	Dec 2, 2025
Grant date	Dec 2, 2025

Abstract

A time-of-flight system includes an emitter-circuit generating and directing pulses of light toward a target, and a receiver-circuit including a photodetector coupled between a bias node and a sensing node to detect pulses that have reflected off the target, a comparison circuit comparing a sense voltage at the sensing node to a reference, a timing measurement circuit measuring elapsed time between generation of a given pulse and detection thereof after reflection off the target, and a programmable current sink that sinks a current from the sensing node equal to a portion of a photocurrent generated by the photodetector due to detection of ambient light. A timing-generation circuit synchronizes generation of the pulses and measurement of elapsed time by the timing circuit. A processor adjusts a magnitude of the current sunk from the sensing node based upon output of the comparison circuit when the emitter circuit is deactivated.

First claim

The invention claimed is:

1 . A time-of-flight ranging system, comprising:
an emitter circuit including a quantum-film based light emitter configured to generate and direct pulses of light toward a target; a receiver circuit comprising:
a quantum-film based photodetector coupled between a bias node and a sensing node, the quantum-film based photodetector configured to detect pulses of the light that have reflected off the target;
a comparison circuit configured to compare a sense voltage at the sensing node to a reference voltage;
a timing measurement circuit configured to measure elapsed time between generation of a given pulse of light by the quantum-film based light emitter and detection of that given pulse of light after reflection off the target; and
a programmable current sink configured to sink a current from the sensing node equal to a portion of a photocurrent generated by the quantum-film based photodetector due to detection of ambient light;
a timing generation circuit configured to generate a timing reference to synchronize generation of the pulses of light and measurement of elapsed time by the timing measurement circuit; and a processor configured to perform a calibration operation to adjust a magnitude of the current sunk from the sensing node based upon output of the comparison circuit when the emitter circuit is deactivated, and to generate ranging data based upon the measured elapsed time.

2 . The time-of-flight ranging system of claim 1 , wherein a quantum-film within the quantum-film based photodetector is formed from quantum dots having cores comprising indium arsenide; wherein a quantum-film within the quantum-film based light emitter is formed from quantum dots having cores comprising indium arsenide; and wherein the pulses of light generated by the emitter circuit are in a short wave infrared spectrum.

3 . The time-of-flight ranging system of claim 1 , wherein the timing measurement circuit comprises a time to digital converter.

4 . The time-of-flight ranging system of claim 1 , wherein the comparison circuit comprises:
a comparator having an inverting terminal coupled to the reference voltage, a non-inverting terminal coupled to the sensing node, and an output coupled to the timing measurement circuit; and a reset switch configured to reset the comparator based upon the output of the comparator.

5 . The time-of-flight ranging system of claim 4 ,
wherein the programmable current sink comprises a programmable current digital to analog converter (DAC) circuit, with the current sunk from the sensing node being set by a control signal provided to the programmable current DAC circuit by the processor.

6 . The time-of-flight ranging system of claim 5 , wherein, during the calibration operation:
the emitter circuit is deactivated; and the processor is configured to:
a) set the control signal to a pre-selected initial value at which it is expected that the current sunk from the sensing node would be less than the portion of the photocurrent generated by the quantum-film based photodetector that is due to detection of ambient light;
b) when the comparator indicates that the sense voltage is greater than the reference voltage during exposure to ambient light, increment the control signal to cause the programmable current DAC circuit to increment the current sunk from the sensing node; and
c) when the comparator indicates that the sense voltage is not greater than the reference voltage during exposure to ambient light, end the calibration operation, and if not, return to b).

7 . A time-of-flight ranging system, comprising:
an emitter circuit including a quantum-film based light emitter configured to generate and direct pulses of light toward a target; a receiver circuit comprising:
a quantum-film based photodetector coupled between a bias node and an intermediate node, the quantum-film based photodetector configured to detect pulses of the light that have reflected off the target;
a current-to-voltage converter coupled between the intermediate node and a sensing node;
a comparison circuit configured to compare a sense voltage at the sensing node to a reference voltage;
a sample/hold circuit coupled to the intermediate node and the sensing node, the sample/hold circuit configured to:
during a calibration operation in which a portion of a photocurrent generated by the quantum-film based photodetector due to detection of ambient light is converted to a calibration voltage by the current-to-voltage converter, sample and hold the calibration voltage; and
during normal operation, generate a current based upon the held calibration voltage and sink that current from the sensing node;

a timing generation circuit configured to generate a timing reference to synchronize generation of the pulses of light and measurement of elapsed time by a timing measurement circuit; and a processor configured to control the sample/hold circuit during the calibration operation, and to generate ranging data based upon the measured elapsed time during normal operation.

8 . The time-of-flight ranging system of claim 7 , wherein a quantum-film within the quantum-film based photodetector is formed from quantum dots having cores comprising indium arsenide; wherein a quantum-film within the quantum-film based light emitter is formed from quantum dots having cores comprising indium arsenide; and wherein the pulses of light generated by the emitter circuit are in a short wave infrared spectrum.

9 . The time-of-flight ranging system of claim 7 , wherein the comparison circuit comprises a comparator having an inverting terminal coupled to the reference voltage, a non-inverting terminal coupled to the sensing node, and an output coupled to the timing measurement circuit.

10 . The time-of-flight ranging system of claim 7 , wherein the timing measurement circuit comprises a time to digital converter.

11 . The time-of-flight ranging system of claim 7 , wherein the current-to-voltage converter comprises a transimpedance amplifier having a non-inverting terminal coupled to ground, an inverting terminal coupled to the intermediate node, and an output coupled to the sample/hold circuit, with a resistance being coupled between the inverting terminal and the output.

12 . The time-of-flight ranging system of claim 11 , wherein the sample/hold circuit comprises:
a current sinking transistor; a switch coupled between the sensing node and a control terminal of the current sinking transistor, the switch being controlled by the processor; a hold capacitor coupled between the control terminal of the current sinking transistor and ground; and a current mirror having an input coupled to a conduction terminal of the current sinking transistor and an output coupled to the intermediate node, the current mirror configured to sink the current based upon the held calibration voltage from the intermediate node during normal operation.

13 . The time-of-flight ranging system of claim 12 , wherein the processor is configured to close the switch during the calibration operation and to open the switch during normal operation.

14 . The time-of-flight ranging system of claim 12 , wherein the current mirror comprises:
a first p-channel transistor having a source coupled to a supply voltage, a drain coupled to the intermediate node, and a gate; and a second p-channel transistor having a source coupled to the supply voltage, a gate coupled to the gate of the first p-channel transistor, and a drain coupled to the gate of the second p-channel transistor and to the conduction terminal of the current sinking transistor.

Assignees

• St Microelectronics Res & Dev Ltd

Inventors

• Dutton Neale

Classifications

• G01S7/497

  Means for monitoring or calibrating · CPC title

• G01S7/4876

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

• G01S17/10

  using transmission of interrupted, pulse-modulated waves (determination of distance by phase measurements G01S17/32) · CPC title

• G01S7/4863

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

• G01S7/484

  Transmitters · CPC title