Device for detecting an object using SPAD photodiodes

• US 9,006,641 B2
• Filed: 01/08/2013
• Issued: 04/14/2015
• Est. Priority Date: 01/09/2012
• Status: Active Grant

• Current Assignee: STMicroelectronics Grenoble 2 SAS (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Grenoble 2 SAS (STMicroelectronics NV)
• Inventors: Drader, Marc
• Primary Examiner(s): LUU, THANH X
• Application Number:
  US13/736,823
• Publication Number:
  US 20130175435A1
• Time in Patent Office: 826 Days
• US Class Current: 250/221
• CPC Class Codes: G01C 3/08 Use of electric radiation detectors
• CPC Class Codes: G01S 17/10 using transmission of interrupted, pulse-modulated waves determination of distance by phase measurements G01S17/32
• CPC Class Codes: G01S 7/4861 Circuits for detection, sampling, integration or read-out
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating

Abstract

The disclosure relates to a method for detecting the presence of an object near a detection device, comprising: emitting pulses of an incident photon beam, detecting photodiodes which trigger avalanche after the reception by the photodiode of at least one photon of a reflected photon beam produced by a reflection of the incident beam on an object near the detection device, determining a distance between the photodiodes and an object in a detection area, as a function of the time between a transmit time of the incident beam and avalanche triggering times of the photodiodes, and correcting the distance determined as a function of a calibration measurement obtained in the absence of object in the detection area, to compensate for photon reflections on a transparent plate arranged between the photodiodes and the detection area.

Claims

1. A method, comprising:

detecting an object in a detection area with a detection device, the detection device having a plurality of single photon avalanche photodiodes, each photodiode having a PN junction having a breakdown voltage, the detection device having a transparent plate between the photodiodes and the detection area, the detecting including;

generating a bias voltage in a bias voltage generation circuit, the bias voltage being greater than the breakdown voltage of the PN junction of each photodiode;

reverse biasing the single photon avalanche photodiodes with the bias voltage;

emitting pulses of an incident photon beam, the pulses of the incident photon beam being configured to generate a reflected photon beam from a reflection on the object;

detecting ones of the photodiodes avalanche triggering in response to receiving at least one photon of the reflected photon beam;

determining a distance between the photodiodes and the object in the detection area, as a function of a transmit time of the incident photon beam and an avalanche triggering time in the photodiodes after receiving at least one photon of the reflected beam;

performing a calibration measurement of the detection area when the detection area is empty;

determining a correction value based on avalanche triggering in the photodiodes in response to reflections of the incident beam by the transparent plate and based on the calibration measurement; and

correcting the distance using the correction value by compensating for avalanche triggering in the photodiodes in response to reflections of the incident beam by the transparent plate.

2. The method of claim 1 wherein determining the correction value includes considering when a first number of photodiodes avalanche triggering based on the reflection from on the plate and a second number of photodiodes avalanche triggering from the reflection by the object are equal.

3. The method of claim 1 wherein determining the correction value includes taking into account a number of photodiodes avalanche triggering based on the reflection by the plate, a number of photodiodes avalanche triggering while obtaining the calibration measurement, and a number of photodiodes triggering avalanche based on the reflection by the object.

4. The method of claim 1, comprising measuring a number of photodiodes avalanche triggering during a measurement cycle, and determining if the number of photodiodes to is lower than a threshold value, the threshold value being associated with no object in the detection area.

5. The method of claim 1 wherein determining the distance includes:

optically coupling a reference set of the single photon avalanche photodiodes to a source of photons emitting the incident photon beam;

reverse biasing the reference set of photodiodes with the bias voltage;

determining the average of avalanche triggering time in the reference set of photodiodes, the distance being determined as a function of the average avalanche triggering time in the reference set of photodiodes.

6. The method of claim 1 wherein determining the distance includes:

generating a first signal at a transmit frequency of the pulses of the incident beam;

synchronizing a start of each pulse of the first signal on the average avalanche triggering time in the photodiodes;

generating a second signal having a first state during a phase-shift period between the first signal and a third signal at the transmit frequency of the pulses of the incident beam; and

when the first signal is synchronized, measuring a duration during which the second signal is in the first state;

the distance being determined as a function of the duration.

7. The method of claim 6 wherein the third signal is a control signal configured to control a source that is configured to emit the incident beam.

8. The method of claim 6, further comprising:

determining transmit times of the pulses of the incident beam by synchronizing the third signal to start each pulse based on the average avalanche triggering time of a reference set of photodiodes of a reference unit, the reference set of photodiodes being reverse biased and optically coupled to the source that is configured to emit the incident beam.

9. A device, comprising:

a transmit circuit configured to emit pulses of an incident photon beam toward a detection area, the pulses of the incident photon beam being configured to generate a reflected photon beam from a reflection on an object;

a detection circuit configured to detect the object in the detection area, the detection circuit including a plurality of single photon avalanche photodiodes, each photodiode having a PN junction having a breakdown voltage, the detection device having a transparent plate between the photodiodes and the detection area, the detection circuit being configured to;

reverse bias the photodiodes with a bias voltage that is greater than the breakdown voltage of the PN junction of each photodiode;

detect ones of the photodiodes avalanche triggering in response to receiving at least one photon of the reflected photon beam;

determine a distance between the photodiodes and the object in the detection area, as a function of a transmit time of the incident photon beam and an avalanche triggering time in the photodiodes after at least one photon of the reflected beam is received;

obtain a calibration measurement of the detection area when the detection area is empty;

determine a correction value based on the calibration measurement, the correction value correspondence to avalanche triggering in the photodiodes in response to reflections of the incident beam by the transparent plate by; and

correct the distance with the correction value.

10. The device of claim 9, comprising a reference detection circuit comprising a reference set of single photon avalanche photodiodes, optically coupled to the transmit circuit to detect a transmit time of each emitted pulse of the incident beam.

11. The device of claim 10 wherein the transmit circuit is configured to be controlled by a control signal, the device further comprising:

a first synchronization circuit configured to output a first signal and configured to synchronize a start of each pulse of the first signal with an average avalanche triggering time of the photodiodes, the pulses of the incident beam having a transmit frequency and the first signal having the transmit frequency, the synchronization circuit comprising;

a phase shifter configured to receive the control signal;

first and second AND logic gates configured to receive the first signal, the logic gates being configured to receive a detection signal from the reception unit that includes a pulse each time one of the photodiodes avalanche triggers; and

a capacitor, the first AND gate being configured to charge the capacitor and the second AND gate being configured to discharge of the capacitor, a voltage across the capacitor being configured to control the phase shifter;

a comparator configured to compare the first signal to a second signal having a frequency of the control signal; and

a duration measurement circuit configured to measure a duration in a high state of an output signal of the comparator.

12. The device of claim 11, comprising a second synchronization circuit configured to synchronize a start of each pulse of the second signal having the transmit frequency of the pulses of the incident beam, on an average avalanche triggering time of the reference set of photodiodes of a reference unit that are configured to be reversed biased and optically coupled to the source, to determine transmit times of the pulses of the incident beam.

13. A method, comprising:

determining a distance between an object in a detection area and a detection device, the detection device having a plurality of single photon avalanche photodiodes, the detection device having a transparent plate between the photodiodes and the detection area, the determining of the distance including;

determining a calibration value associated with a number of photodiodes avalanche triggering in response to reflections of an incident photon beam from the transparent plate when the object is not in the detection area;

determining an intermediate measurement associated with a number of photodiodes avalanche triggering in response to reflections of the incident photon beam from the object and the transparent plate; and

generating the distance by adjusting the intermediate measurement with the calibration value.

14. The method of claim 13 wherein determining the distance includes detecting a transmit time of the incident photon beam, the transmit time being a time between emission of the incident photon beam from a source and at least one of the photodiodes avalanche triggering in response to a photon from the incident photon beam.

15. The method of claim 13 wherein determining the distance includes comparing the intermediate measurement with a threshold value, the threshold value being associated with parasitic photon reflections from the plate.

16. The method of claim 15, further comprising returning a null signal when the intermediate measurement is lower than the threshold value, the null signal representing no object in the detection area.