LIDAR SCANNER CALIBRATION

• US 20160306032A1
• Filed: 11/21/2014
• Published: 10/20/2016
• Est. Priority Date: 11/22/2013
• Status: Active Grant

• Current Assignee: Uatc, LLC (Uber Technologies, Inc.)
• Original Assignee: Brent S. Schwarz, James A. Haslim, Michael D. Karasoff, Nicholas M. Iturraran
• Inventors: Schwarz, Brent S., Haslim, James A., Iturraran, Nicholas M., Karasoff, Michael D.
• Granted Patent: US 9,772,399 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01S 17/14 wherein a voltage or current pulse is initiated and terminated in accordance with the pulse transmission and echo reception respectively, e.g. using counters
• CPC Class Codes: G01S 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 7/4812 transmitted and received beams following a coaxial path
• CPC Class Codes: G01S 7/4818 using optical fibres
• 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
• CPC Class Codes: G01S 7/4972 Alignment of sensor

Abstract

A LiDAR can include a laser, an avalanche photodiode, a splitter, and a processor. The laser can be configured to emit a narrow electromagnetic pulse. The avalanche photodiode can be configured to receive one or more electromagnetic pulses and output a response signal in response to said pulses. The photodiode can also be positioned to receive at least one reflected pulse, reflected by an object external from the LiDAR sensor and caused by the laser. The avalanche photodiode can also have a bias voltage applied to it affecting the response signal. The splitter can be positioned to receive the narrow electromagnetic pulse and split it into at least one external pulse directed toward the object external from the LiDAR sensor and at least one calibration pulse directed toward the photodiode. The calibration pulse directed toward the photodiode can be received by the photodiode before the pulse reflected by the object. The processor can be configured to receive response signals from the photodiode. Further, the processor can be configured to adjust the bias voltage according to a response signal caused by the calibration pulse to compensate for temperature changes of the photodiode.

Claims

1. A LiDAR sensor comprising:

a laser configured to emit a narrow electromagnetic pulse;

an avalanche photodiode configured to receive one or more electromagnetic pulses and output a response signal in response to said pulses, the avalanche photodiode being positioned to receive at least one reflected pulse being reflected by an object external from the LiDAR sensor caused by the laser, the avalanche photodiode having a bias voltage applied to it affecting the response signal;

a splitter positioned to receive the narrow electromagnetic pulse and split it into at least one external pulse directed toward the object external from the LiDAR sensor and at least one calibration pulse directed toward the avalanche photodiode, the calibration pulse directed toward the photodiode being received by the avalanche photodiode before the pulse reflected by the object; and

a processor configured to receive response signals from the avalanche photodiode, the processor further configured to adjust the bias voltage according to a response signal caused by the calibration pulse to compensate for temperature changes of the avalanche photodiode.

2. The LiDAR sensor of claim 1, wherein the processor is configured to adjust the bias voltage in real-time in response to response signals caused by the calibration pulse.

3. The LiDAR sensor of claim 1, wherein the temperature of the avalanche photodiode is not directly measured.

4. The LiDAR sensor of claim 1, wherein the processor is configured to adjust the bias voltage such that a gain of the avalanche photodiode in response to a given detected pulse is held substantially constant.

5. The LiDAR sensor of claim 1, wherein the processor is configured to adjust the bias voltage to have a constant offset below a breakdown voltage of the avalanche photodiode.

6. The LiDAR sensor of claim 1, further comprising a resistor between an anode of the avalanche photodiode and a lower potential, and a second diode between the anode of the avalanche photodiode and the lower potential, the anode of the second diode being connected toward the anode of the avalanche photodiode, and the resistor and the second diode being connected in parallel.

7. The LiDAR sensor of claim 1, comprising a means for adjusting response signals from the avalanche photodiode such that the response signal is substantially linear in response to weak pulses and substantially logarithmic in response to strong pulses.

8. The LiDAR sensor of claim 1, wherein the processor is further configured to measure a strength of the reflected pulse.

9. The LiDAR sensor of claim 1, wherein the processor is configured to adjust the bias voltage according to the response signal prior to receiving the reflected pulse.

10. A method for measuring a reflected electromagnetic pulse comprising:

emitting an electromagnetic pulse;

splitting the emitted electromagnetic pulse into at least an external pulse and a calibration pulse;

directing the calibration pulse toward an avalanche photodiode;

directing the external pulse toward an object to be measured, causing a reflected pulse;

applying an initial bias voltage to the avalanche photodiode;

receiving with the avalanche photodiode the calibration pulse while the avalanche photodiode is under the initial bias voltage;

measuring a response from the avalanche photodiode caused by the calibration pulse;

applying a desired bias voltage to the avalanche photodiode, using the measured response caused by the calibration pulse, to adjust for temperature changes of the avalanche photodiode;

receiving with the avalanche photodiode the reflected pulse; and

measuring a response from the avalanche photodiode caused by the reflected pulse.

11. The method of claim 10, further comprising the step of estimating the strength of the reflected pulse.

12. The method of claim 10, wherein the method is repeated continuously, such that the desired bias voltage is applied to compensate for temperature changes of the avalanche photodiode in real-time.

13. The method of claim 10, wherein the temperature of the avalanche photodiode is not directly measured to compensate for temperature changes of the avalanche photodiode.

14. The method of claim 10, further comprising estimating a desired bias voltage based on the measured response from the avalanche photodiode caused by the calibration pulse.

15. The method of claim 10, further comprising estimating a temperature of the avalanche photodiode based on the measured response from the avalanche photodiode caused by the calibration pulse.

16. The method of claim 15, wherein the step of estimating is done without measuring a temperature of the avalanche photodiode.

17. The method of claim 10, further comprising adjusting the response from the avalanche photodiode caused by the reflected pulse such that the strength of the response is substantially linear in response to weak pulses and substantially logarithmic in response to strong pulses.

18. The method of claim 10, further comprising:

splitting the calibration pulse to create at least a second calibration pulse;

delaying the second calibration pulse;

directing the second calibration pulse toward the avalanche photodiode;

receiving with the avalanche photodiode the second calibration pulse after receiving the calibration pulse and before receiving the reflected pulse; and

measuring a response from the avalanche photodiode caused by the second calibration pulse,

wherein the step of applying a desired bias voltage to the avalanche photodiode, using the measured response caused by the calibration pulse further comprises using the measured response from the second calibration pulse.

19. The method of claim 10, wherein the step of applying a preferred bias voltage to the avalanche photodiode, using the measured response caused by the calibration pulse comprises adjusting the bias voltage such that a gain of the avalanche photodiode in response to a given detected pulse is held substantially constant.

20. The method of claim 10, wherein the step of applying a preferred bias voltage to the avalanche photodiode, using the measured response caused by the calibration pulse comprises adjusting the bias voltage such that an offset between the bias voltage and a breakdown voltage of the avalanche photodiode is held substantially constant.

21. The method of claim 10, wherein the reflected pulse is received while the avalanche photodiode is under the desired bias voltage.

22. A LiDAR sensor comprising:

a laser configured to emit a narrow electromagnetic pulse;

an avalanche photodiode configured to receive one or more electromagnetic pulses and output a response signal in response to said pulses, the avalanche photodiode being positioned to receive at least one reflected pulse being reflected by an object external from the LiDAR sensor caused by the laser, the avalanche photodiode having a bias voltage affecting the response signal;

a splitter positioned to receive the narrow electromagnetic pulse and split it into at least one external pulse directed toward the object external from the LiDAR sensor and at least one calibration pulse directed toward the avalanche photodiode, the calibration pulse directed toward the avalanche photodiode being received by the avalanche photodiode before the pulse reflected by the object; and

a means for adjusting the bias voltage to compensate for temperature variations without measuring temperature.

23. The LiDAR sensor of claim 22, further comprising a means for adjusting the response from the avalanche photodiode caused by the reflected pulse such that the strength of the response is substantially linear in response to weak pulses and substantially logarithmic in response to strong pulses.