Power efficient pulsed laser driver for time of flight cameras
View Patent ↗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.
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.