Laser diode timing feedback using trace loop

• US 9,784,835 B1
• Filed: 09/27/2013
• Issued: 10/10/2017
• 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): Ratcliffe, Luke
• Assistant Examiner(s): Abraham, Samantha K
• Application Number:
  US14/039,817
• Time in Patent Office: 1,474 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. An apparatus, comprising:

a transistor coupled to a current path and configured to change a current flow through the current path in response to an initiating signal;

a light emitting element coupled to the transistor via the current path and configured to emit a light pulse responsive to the change in the 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 detect the voltage induced in the conductive loop and to determine an emission time of the emitted light pulse based on the detected voltage.

2. The apparatus of claim 1, 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.

3. The apparatus of claim 2, wherein at least a portion of the conductive loop overlaps at least a portion of the discharge path.

4. The apparatus of claim 1, 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.

5. The apparatus of claim 1, wherein the transistor and light emitting element are 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.

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

7. The apparatus of claim 1, wherein the transistor is an avalanche transistor.

8. The apparatus of claim 7, wherein the initiating signal comprises a signal applied to a base of the avalanche transistor and the current path is coupled to a collector of the avalanche transistor.

9. The apparatus of claim 1, wherein the transistor is a Gallium nitride field effect transistor (GaNFET).

10. The apparatus of claim 9, wherein the initiating signal comprises a signal applied to a gate of the GaNFET and the current path is coupled to a drain of the GaNFET.

11. A method, comprising:

applying an initiating signal to a transistor, wherein the transistor is coupled to a light emitting element via a current path and configured to change a current flow through the current path in response to the initiating signal, and wherein the light emitting element is configured to emit a light pulse 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 pulse based on the detected voltage.

12. The method of claim 11, further comprising:

emitting the light pulse toward a reflective object;

detecting a returning reflected light signal that comprises light from the emitted light pulse 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.

13. The method of claim 12, 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.

14. The method of claim 11, 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.

15. The method of claim 14, wherein at least a portion of the conductive loop overlaps the discharge path.

16. The method of claim 11, 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.

17. The method of claim 11, 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.

18. The method of claim 11, wherein the light emitting element is a laser diode.

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

a light source including;

a transistor coupled to a current path and configured to change a current flow through the current path in response to an initiating signal;

a light emitting element coupled to the transistor via the current path and configured to emit a light pulse responsive to the change in the 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 detect the voltage induced in the conductive loop and to determine an emission time of the emitted light pulse based on the detected voltage;

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

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

20. The LIDAR device of claim 19, wherein the light source further includes 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, and wherein at least a portion of the conductive loop overlaps at least a portion of the discharge path.