Power efficient pulsed laser driver for time of flight cameras

• US 9,442,195 B2
• Filed: 10/11/2013
• Issued: 09/13/2016
• Est. Priority Date: 10/11/2012
• Status: Active Grant

• Current Assignee: Lumentum Operations, LLC (Lumentum Holdings Inc.)
• Original Assignee: Lumentum Operations, LLC (Lumentum Holdings Inc.)
• Inventors: Tien, An-Chun, Morales, Lucas, Wong, Vincent V.
• Primary Examiner(s): Ratcliffe, Luke
• Assistant Examiner(s): Abraham, Samantha K
• Application Number:
  US14/051,986
• Publication Number:
  US 20140104592A1
• Time in Patent Office: 1,068 Days
• US Class Current: 1/1
• CPC Class Codes: G01S 17/08 for measuring distance only indirect measurement G01S17/46; active triangulation systems G01S17/48
• CPC Class Codes: G01S 17/894 3D imaging with simultaneous measurement of time-of-flight at a 2D array of receiver pixels, e.g. time-of-flight cameras or flash lidar
• CPC Class Codes: G01S 7/4911 Transmitters

Abstract

A time of flight camera device comprises an light source for illuminating an environment including an object with light of a first wavelength; an image sensor for measuring time the light has taken to travel from the light source to the object and back; optics for gathering reflected light from the object and imaging the environment onto the image sensor; driver electronics for controlling the light source with a high speed signal at a clock frequency; and a controller for calculating the distance between the object and the illumination unit. To minimize power consumption and resulting heat dissipation requirements, the light source/driver electronics are operated at their resonant frequency. Ideally, the driver electronics includes a reactance adjuster for changing a resonant frequency of the illumination unit and driver electronics system.

Claims

1. A method of operating a time of flight camera comprising:

selecting, by the time of flight camera, a clock frequency such that a light source and driver electronics operate at a resonant frequency, the clock frequency being selected by;

scanning the clock frequency across a particular operating range,

measuring a particular amount of required current,

identifying, based on scanning the clock frequency and measuring the particular amount of required current, a particular frequency, and

using the particular frequency as the clock frequency;

controlling, by the time of flight camera and using the driver electronics, the light source with a high speed signal at the clock frequency;

illuminating, by the time of flight camera and based on controlling the light source, an environment, including an object, with light from the light source;

gathering, by the time of flight camera and based on illuminating the environment, reflected light and imaging the environment onto an image sensor; and

calculating, by the time of flight camera and based on gathering the reflected light, a distance between the object and the light source.

2. The method according to claim 1, wherein the light is modulated at between 20 MHz to 200 MHz.

3. The method according to claim 1, wherein the light source comprises an LED or a laser diode.

4. The method according to claim 1, wherein the light source generates infrared light.

5. The method according to claim 1, further comprising:

an optical band pass filter for passing the light and suppressing background light.

6. The method according to claim 1, wherein

the light source comprises RF-modulated light sources with phase detectors by modulating an outgoing beam with an RF carrier, and

the method further includes:

measuring a phase shift of the RF carrier at the image sensor.

7. The method according to claim 1, wherein

the particular frequency occurs at a point of minimum power required.

8. The method according to claim 1, further comprising:

adjusting the resonant frequency of the light source and driver electronics system.

9. The method according to claim 8, wherein adjusting the resonant frequency includes:

selecting between one of a plurality of reactant component networks to communicatively couple to the driver electronics.

10. The method according to claim 1, wherein the resonant frequency is a relaxation resonant frequency.

11. The method according to claim 1, further comprising:

providing a transistor, including a base and a collector, in series with the light source,

providing a photodetector, in parallel with the light source, for receiving a portion of the light from the light source and generating an AC electrical component; and

feeding back the AC electrical component to the base of the transistor.

12. A time of flight camera device comprising:

a light source for illuminating an environment including an object with light;

an image sensor for measuring a time the light has taken to travel from the light source to the object and back;

optics for gathering reflected light from the object and imaging the environment onto the image sensor;

driver electronics for controlling the light source with a high speed signal at a clock frequency, whereby the light source and the driver electronics operate at a resonant frequency, the clock frequency being selected by;

scanning the clock frequency across a particular operating range,

measuring a particular amount of required current,

identifying, based on scanning the clock frequency and measuring the particular amount of required current, a particular frequency, and

using the particular frequency as the clock frequency; and

a controller for calculating a distance between the object and the light source.

13. The time of flight camera device according to claim 12, wherein the driver electronics includes a reactance adjuster for changing the resonant frequency of the light source and the driver electronics.

14. The time of flight camera device according to claim 13, wherein the reactance adjuster includes a plurality of network segments, each with different reactance, and a switch for selecting one of the plurality of network segments.

15. The time of flight camera device according to claim 14, wherein each network segment, of the plurality of network segments, includes a capacitor with a different capacitance.

16. The time of flight camera device according to claim 14, wherein each network segment, of the plurality of network segments, includes an inductor with a different inductance.

17. The time of flight camera device according to claim 12, wherein the clock frequency is between 20 MHz and 200 MHz.

18. The time of flight camera device according to claim 12, wherein

the light source comprises an RF-modulated light source with phase detectors by modulating an outgoing beam with an RF carrier, and

the controller measures a phase shift of the RF carrier at the image sensor.

19. The time of flight camera device according to claim 12, wherein

the resonant frequency is a relaxation resonant frequency;

and

the time of flight camera device further includes;

a feedback circuit for driving the light source at the relaxation resonant frequency.

20. The time of flight camera device according to claim 19, wherein the feedback circuit comprises:

a transistor, including a base, in series with the light source; and

a photodetector, in parallel with the light source, for receiving a portion of the light from the light source and generating an AC electrical component for feeding back to the base of the transistor.