Laser diode timing feedback using trace loop

• US 10,007,000 B1
• Filed: 10/09/2017
• Issued: 06/26/2018
• Est. Priority Date: 09/27/2013
• Status: Active Grant

• Current Assignee: Waymo LLC (Alphabet Inc.)
• Original Assignee: Waymo LLC (Alphabet Inc.)
• Inventors: Droz, Pierre-yves, Pennecot, Gaetan
• Primary Examiner(s): Abraham, Samantha K
• Application Number:
  US15/728,065
• Time in Patent Office: 260 Days
• CPC Class Codes: G01S 17/08 for measuring distance only indirect measurement G01S17/46; active triangulation systems G01S17/48
• 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 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 7/4817 relating to scanning
• CPC Class Codes: G01S 7/484 Transmitters
• CPC Class Codes: G01S 7/4865 Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak peak detection in noise, signal conditioning G01S7/487
• CPC Class Codes: G08G 1/16 Anti-collision systems road vehicle drive control systems for predicting or avoiding probable or impending collision otherwise than by control of a particular sub-unit B60W30/08
• CPC Class Codes: G08G 1/165 for passive traffic, e.g. including static obstacles, trees
• CPC Class Codes: G08G 1/166 for active traffic, e.g. moving vehicles, pedestrians, bikes
• CPC Class Codes: H01S 5/06 Arrangements for controlling the laser output parameters, e.g. by operating on the active medium

Abstract

A laser diode firing circuit for a light detection and ranging (LIDAR) device that includes an inductively coupled feedback system is disclosed. The firing circuit includes a laser diode coupled in series with a transistor, such that current through the laser diode is controlled by the transistor. The laser diode is configured to emit a pulse of light in response to current flowing through the laser diode. A feedback loop is positioned to be inductively coupled to a current path of the firing circuit that includes the laser diode. As such, a change in current flowing through the laser diode induces a voltage in the feedback loop. A change in voltage across the leads of the feedback loop can be detected and the timing of the voltage change can be used to determine the time that current begins flowing through the laser diode.

Claims

1. A system comprising:

a current path, wherein the current path comprises a light emitting element configured to emit light responsive to a change in current flow through the current path;

a conductive loop inductively coupled to the current path such that the change in current flow through the current path induces a voltage in the conductive loop; and

a circuit configured to determine an emission time of the emitted light, wherein determining the emission time comprises detecting a time associated with the voltage induced in the conductive loop.

2. The system of claim 1, further comprising a transistor coupled to the current path, wherein the transistor is configured to change the current flow through the current path.

3. The system of claim 2, further comprising a capacitor and a voltage supply, wherein the capacitor is configured to be charged by the voltage supply via a charging path and to discharge through a discharge path comprising the light emitting element, current path, and transistor.

4. The system of claim 2, wherein the transistor is an avalanche transistor or a Gallium nitride field effect transistor (GaNFET).

5. The system of claim 2, wherein the transistor is on one side of a printed circuit board (PCB) and the conductive loop is on an opposite side of the PCB.

6. The system of claim 1, wherein the light emitting element is a laser diode.

7. The system of claim 1, wherein the light emitting element is mounted to at least one side of a printed circuit board (PCB) and the conductive loop is disposed in an internal layer of the PCB.

8. The system of claim 1, further comprising:

a photo detector configured to receive a reflected portion of light emitted from the light emitting element at a reception time; and

a controller configured to determine, based on a difference between the reception time and the determined emission time, a distance between the light emitting element and a reflective element in an environment of the system.

9. A method, comprising:

changing a current flow through a current path, wherein the current path comprises a light emitting element, wherein the light emitting element is configured to emit light responsive to the change in the current flow through the current path;

detecting, in a conductive loop inductively coupled to the current path, a voltage induced by the change in the current flow through the current path; and

determining an emission time of the emitted light based on the detected voltage.

10. The method of claim 9, further comprising:

emitting the emitted light toward a reflective object;

detecting a returning reflected light signal that comprises light from the emitted light reflected by the reflective object; and

determining a distance to the reflective object based on the determined emission time and a reception time of the detected reflected light signal.

11. The method of claim 10, further comprising:

identifying an obstacle surrounding an autonomous vehicle based on the reflected light signal; and

controlling the autonomous vehicle to avoid the identified obstacle.

12. The method of claim 9, wherein the current path is coupled to a transistor, further comprising:

applying an initiating signal to the transistor, wherein the applied initiating signal causes the change in current flow through the current path.

13. The method of claim 12, further comprising

charging a capacitor from a voltage supply via a charging path;

and

discharging the capacitor through a discharge path comprising the light emitting element, current path, and transistor.

14. The method of claim 12, wherein the transistor comprises an avalanche transistor, wherein the initiating signal is applied to a base of the avalanche transistor, and wherein the current path is coupled to a collector of the avalanche transistor.

15. The method of claim 12, wherein the transistor comprises a Gallium nitride field effect transistor (GaNFET), wherein the initiating signal is applied to a gate of the GaNFET and the current path is coupled to a drain of the GaNFET.

16. The method of claim 9, wherein at least a portion of the conductive loop overlaps the discharge path.

17. The method of claim 9, wherein the light emitting element is a laser diode, and wherein the emitted light comprises a light pulse.

18. A light detection and ranging (LIDAR) device comprising:

a current path, wherein the current path comprises a light emitting element configured to emit light responsive to a change in current flow through the current path;

a conductive loop inductively coupled to the current path such that the change in current flow through the current path induces a voltage in the conductive loop; and

a circuit configured to determine an emission time of the emitted light, wherein determining the emission time comprises detecting a time associated with the voltage induced in the conductive loop.

19. The LIDAR of claim 18, further comprising a transistor coupled to the current path, wherein the transistor is configured to change the current flow through the current path responsive to receiving an initiating signal.

20. The LIDAR of claim 18, further comprising:

a light sensor configured to detect a reflected light signal comprising light from the emitted light reflected by a reflective object; and

a controller configured to determine a reception time of the reflected light signal and determine a distance to the reflective object based on the emission time and the reception time.