Dynamic control of diode bias voltage (photon-caused avalanche)

• US 9,048,370 B1
• Filed: 03/14/2013
• Issued: 06/02/2015
• Est. Priority Date: 03/14/2013
• Status: Active Grant

• Current Assignee: Waymo LLC (Alphabet Inc.)
• Original Assignee: Google Inc. (Alphabet Inc.)
• Inventors: Droz, Pierre-yves, Urmson, Chris, Wachter, Luke
• Primary Examiner(s): Ratcliffe, Luke
• Assistant Examiner(s): RODRIGUEZ, VICENTE M
• Application Number:
  US13/804,455
• Time in Patent Office: 810 Days
• Field of Search: 356/5.01
• US Class Current: 1/1
• CPC Class Codes: G01R 31/2635 Testing light-emitting diodes, laser diodes or photodiodes
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating
• CPC Class Codes: H01L 31/02027 for devices working in avalanche mode
• CPC Class Codes: H01L 31/107 the potential barrier working in avalanche mode, e.g. avalanche photodiodes

Abstract

Methods and devices are provided for determining an operating bias voltage of a photodiode. One example method includes (i) varying a bias voltage of a photodiode; (ii) detecting spurious signals generated by the photodiode while varying the bias voltage of the photodiode; (iii) determining a threshold bias voltage at which a frequency of occurrence of the spurious signals reaches a threshold frequency; (iv) determining an operating bias voltage for the photodiode based on at least the threshold bias voltage; and (v) operating the photodiode with the operating bias voltage in a light-detection and ranging (LIDAR) system.

Claims

1. A method comprising:

varying a bias voltage of a photodiode;

detecting spurious signals generated by the photodiode while varying the bias voltage of the photodiode;

determining, for each of one or more bias voltages, a respective frequency of occurrence of the spurious signals;

determining a threshold bias voltage at which a frequency of occurrence of the spurious signals reaches a threshold frequency;

determining an operating bias voltage for the photodiode based on at least the threshold bias voltage; and

operating the photodiode with the operating bias voltage in a light-detection and ranging (LIDAR) system.

2. The method of claim 1, wherein the photodiode comprises an avalanche photodiode.

3. The method of claim 1, wherein varying the bias voltage of the photodiode comprises increasing the bias voltage of the photodiode.

4. The method of claim 3, wherein increasing the bias voltage of the photodiode comprises increasing the bias voltage substantially linearly.

5. The method of claim 1, wherein varying the bias voltage of the photodiode comprises applying at least one bias voltage between 150 volts and 220 volts.

6. The method of claim 1, wherein determining the operating bias voltage for the photodiode based on at least the threshold bias voltage comprises setting the operating bias voltage to be a predetermined amount less than the threshold bias voltage.

7. The method of claim 6, wherein the predetermined amount is between 2 volts and 3 volts.

8. The method of claim 1, further comprising:

determining one or more additional threshold bias voltages by a process comprising detecting additional spurious signals generated by the photodiode while additionally varying the bias voltage of the photodiode; and

wherein determining the operating bias voltage for the photodiode based on at least the threshold bias voltage comprises determining the operating bias voltage based on at least the threshold bias voltage and the one or more additional threshold bias voltages.

9. The method of claim 8, wherein determining the operating bias voltage based on at least the threshold bias voltage and the one or more additional threshold bias voltages comprises determining the operating bias voltage based on an average of the threshold bias voltage and the one or more additional threshold bias voltages.

10. The method of claim 8, wherein determining the operating bias voltage based on at least the threshold bias voltage and the one or more additional threshold bias voltages comprises determining the operating bias voltage based on a weighted average of the threshold bias voltage and the one or more additional threshold bias voltages.

11. A method comprising:

operating a photodiode in an online mode in which the photodiode receives one or more light pulses transmitted by a light-detection and ranging (LIDAR) system;

after operating the photodiode in the online mode, operating the photodiode in an offline mode in which the photodiode does not receive light pulses transmitted by the LIDAR system, wherein operating the photodiode in the offline mode comprises;

varying a bias voltage of the photodiode;

detecting spurious signals generated while varying the bias voltage of the photodiode;

determining, for each of one or more bias voltages, a respective frequency of occurrence of the spurious signals;

determining a threshold bias voltage at which a frequency of occurrence of the spurious signals reaches a threshold frequency; and

determining an operating bias voltage for the photodiode based on at least the threshold bias voltage; and

after operating the photodiode in the offline mode, operating the photodiode in a subsequent online mode in which the photodiode receives one or more light pulses transmitted by the LIDAR system, wherein operating the photodiode in the subsequent online mode comprises operating the photodiode with the operating bias voltage.

12. The method of claim 11, further comprising operating the photodiode in additional offline modes to determine additional operating bias voltages and operating the photodiode in additional online modes with the additional operating bias voltages.

13. The method of claim 12, further comprising scheduling the additional offline modes based on one or more environmental factors.

14. The method of claim 12, further comprising scheduling the additional offline modes to occur at fixed time intervals.

15. A light-detection and ranging (LIDAR) device, comprising:

a light source, wherein the light source is configured to emit light pulses;

a photodiode, wherein the photodiode is configured to receive light pulses that have been transmitted by the light source and reflected by one or more objects in an environment of the LIDAR device;

a voltage source configured to apply a bias voltage to the photodiode;

and a controller configured to;

control the power source to vary the bias voltage applied to the photodiode;

detect spurious signals generated by the photodiode while varying the bias voltage;

determine, for each of one or more bias voltages, a respective frequency of occurrence of the spurious signals;

determine a threshold bias voltage at which a frequency of occurrence of the spurious signals reaches a threshold frequency;

determine an operating bias voltage based on at least the threshold bias voltage; and

control the voltage source to apply the operating bias voltage to the photodiode.

16. The LIDAR device of claim 15, wherein the photodiode comprises an avalanche photodiode.

17. The LIDAR device of claim 15, wherein the controller is configured to detect spurious signals generated by the photodiode while varying the bias voltage during each of a plurality of offline modes in which the photodiode does not receive light pulses transmitted by the light source.

18. The LIDAR device of claim 15, wherein the controller is configured to schedule the offline modes to occur at fixed intervals.

19. The LIDAR device of claim 15, wherein the controller is configured to schedule the offline modes based on one or more environmental factors.

20. The LIDAR device of claim 15, wherein the controller is configured to set the operating bias voltage to be less than the threshold bias voltage by a predetermined amount.