POWER EFFICIENT PULSED LASER DRIVER FOR TIME OF FLIGHT CAMERAS

• US 20140104592A1
• Filed: 10/11/2013
• Published: 04/17/2014
• Est. Priority Date: 10/11/2012
• Status: Active Grant

• Current Assignee: Lumentum Operations, LLC (Lumentum Holdings Inc.)
• Original Assignee: An-Chun Tien, Lucas Morales
• Inventors: TIEN, An-Chun, Wong, Vincent V., Morales, Lucas
• Granted Patent: US 9,442,195 B2
• Time in Patent Office: Days
• US Class Current: 356/5.01
• 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:

illuminating an environment, including an object, with light of a first wavelength from a light source;

controlling the light source with a high speed signal at a clock frequency using driver electronics;

selecting the clock frequency, whereby the light source and driver electronics is at resonance;

gathering reflected light and imaging the environment onto an image sensor; and

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

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 3, wherein the light source generates infrared light.

5. The method according to claim 1, further comprising an optical band pass filter, which only passes the light of the first wavelength for suppressing background light.

6. The method according to claim 1, wherein the light source comprises RF-modulated light sources with phase detectors by modulating the outgoing beam with an RF carrier, and wherein the calculating step includes measuring the phase shift of the carrier at the image sensor.

7. The method according to claim 1, wherein the step of selecting the clock frequency comprises:

scanning the driver electronics through a range of frequencies, while measuring current required to power the light source; and

determining the clock frequency at a point of minimum power required.

8. The method according to claim 7, further comprising adjusting the resonant frequency of the light source and driver electronics system.

9. The method according to claim 7, wherein the step of adjusting the resonant frequency comprises selecting between one of a plurality of reactant component networks to couple to the driver electronics.

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

11. The method according to claim 10, wherein the step of selecting the clock frequency comprises:

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

providing a photodetector in parallel with the light source 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 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, whereby the light source and driver electronics is at resonance; and

a controller for calculating the distance between the object and the illumination unit.

13. The device according to claim 12, wherein the driver electronics includes a reactance adjuster for changing a resonant frequency of the illumination unit and driver electronics system.

14. The 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 device according to claim 14, wherein each network segment includes a capacitor with a different capacitance.

16. The device according to claim 14, wherein each network segment includes an inductor with a different inductance.

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

18. The device according to claim 12, wherein the light source comprises an RF-modulated light source with phase detectors by modulating the outgoing beam with an RF carrier, and wherein the controller measures the phase shift of the carrier at the image sensor.

19. The device according to claim 12, wherein the resonant frequency is the relaxation resonant frequency;

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

20. The device according to claim 19, wherein the feedback circuit comprises:

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

a photodetector in parallel with the light source 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.