LIDAR data acquisition and control
Methods and systems for performing three dimensional LIDAR measurements with an integrated LIDAR measurement device are described herein. In one aspect, a return signal receiver generates a pulse trigger signal that triggers the generation of a pulse of illumination light and data acquisition of a return signal, and also triggers the time of flight calculation by time to digital conversion. In addition, the return signal receiver also estimates the width and peak amplitude of each return pulse, and samples each return pulse waveform individually over a sampling window that includes the peak amplitude of each return pulse waveform. In a further aspect, the time of flight associated with each return pulse is estimated based on a coarse timing estimate and a fine timing estimate. In another aspect, the time of flight is measured from the measured pulse due to internal optical crosstalk and a valid return pulse.
1. An integrated LIDAR measurement device, comprising:
a printed circuit board having an illumination driver mounted thereto; and
a return signal receiver mounted to the printed circuit board,
wherein the return signal receiver is configured to, in response to receiving a command signal, generate a trigger signal and communicate the trigger signal to the illumination driver;
wherein the return signal receiver is configured to determine a time of flight associated with each of one or more return light signals.
2. The integrated LIDAR measurement system of claim 1 , further comprising
an illumination source mounted to the printed circuit board; and
a photodetector mounted to a substrate, the photodetector configured to detect an amount of return light received by the photodetector in response to a measurement beam of illumination light and generate an output signal indicative of the detected amount of return light;
wherein the illumination driver is configured to selectively couple the illumination source to an electrical power source in response to the trigger signal, to cause the illumination source to emit the measurement beam of illumination Ii alit.
3. The integrated LIDAR measurement device of claim 2 , wherein the return signal receiver includes a return signal analysis module, wherein the return signal analysis module comprises:
a constant fraction discriminator module having a first input node, a second input node, and an output node, wherein the output signal is received on the first input node, and wherein the constant fraction discriminator module is configured to switch a hit signal at the output node to a different value when the output signal exceeds a threshold voltage value on the second input node.
4. The integrated LIDAR measurement device of claim 3 , wherein the return signal analysis module further comprises:
a coarse timing module having a first input node coupled to the output node of the constant fraction discriminator, a second input node, and an output node, wherein the second input node of the coarse timing module is coupled to receive the trigger signal, and wherein the coarse timing module is configured to generate a digital value at the output node of the coarse timing module indicative of a time elapsed between a transition of the trigger signal and a transition of the hit signal.
5. The integrated LIDAR measurement device of claim 4 , wherein the digital value is a count of a number of transitions of a digital clock signal that occur between the transition of the trigger signal and the transition of the hit signal.
6. The integrated LIDAR measurement device of claim 5 , wherein the return signal analysis module further comprises:
a fine timing module having a first input node, a first output node, and a second output node, wherein the first input node of the fine timing module is coupled to receive the hit signal,
wherein the fine timing module is configured to generate (i) a first electrical signal at the first output node of the fine timing module indicative of a time difference between the transition of the hit signal and a subsequent transition of the digital clock signal and (ii) a second electrical signal at the second output node of the fine timing module indicative of a time difference between the transition of the hit signal and a subsequent transition of an inverse of the digital clock signal.
7. The integrated LIDAR measurement device of claim 5 , wherein the coarse timing module is configured to generate a metastability signal, wherein the metastability signal is the digital clock signal shifted by half of a period of the digital clock signal.
8. The integrated LIDAR measurement device of claim 7 , further comprising:
a time of flight module configured to estimate a value of a time of flight of the measurement beam of illumination light based at least in part on the digital value indicative of the time elapsed between the transition of the trigger signal and the transition of the hit signal, the time difference between the transition of the hit signal and the subsequent transition of the digital clock signal, the time difference between the transition of the hit signal and the subsequent transition of the inverse of the digital clock signal, and the metastability signal.
9. The integrated LIDAR measurement device of claim 3 , the return signal analysis module further comprising:
a pulse width detection module including:
a first input node coupled to receive the hit signal,
a second input node coupled to receive an enable signal, and
an output node, wherein the pulse width detection module is configured to generate an electrical signal at the output node of the pulse width detection module that is indicative of a time difference between a transition of the enable signal and a time when an amplitude of the hit signal falls below a threshold value.
10. The integrated LIDAR measurement device of claim 3 , the return signal analysis module further comprising:
a return signal sample and hold module configured to generate an amplitude signal indicative of a peak amplitude of the output signal after the transition of the hit signal.
11. The integrated LIDAR measurement device of claim 10 , wherein the return signal sample and hold module is further configured to generate a plurality of output signal samples each indicative of a respective amplitude of the output signal before or after the peak amplitude.
12. The integrated LIDAR measurement device of claim 11 , wherein a number of output signal samples before or after the peak amplitude is programmable.
13. The integrated LIDAR measurement device of claim 2 , wherein a first of the one or more return light signals is due to optical crosstalk between the illumination source and the photodetector, and wherein the time of flight associated with each subsequent return light signal of the one or more return light signals is determined with reference to the first return light signal.
14. The integrated LIDAR measurement device of claim 1 , wherein a duration of a measurement window is approximately a time of flight of light from the LIDAR measurement device to a specified range of the LIDAR measurement device and back to the LIDAR measurement device.
15. A method comprising:
communicating, by a return signal receiver a trigger signal to an illumination driver mounted to a printed circuit board, the trigger signal configured to cause the illumination driver to selectively electrically couple an illumination source to an electrical power source, to cause the illumination source to emit a measurement beam of illumination light;
receiving, by the return signal receiver MCA during a duration of a measurement window, from a photodetector mounted to a substrate, an output signal indicative of a detected amount of return light received by the photodetector in response to the measurement beam of illumination light;
identifying, by the return signal receiver, one or more return light signals of the detected return light; and
determining, by the return signal receiver, a time of flight associated with each of the one or more return light signals.
16. The method of claim 15 , further comprising:
generating a hit signal that switches to a different value when the output signal exceeds a threshold voltage value; and
generating a digital value indicative of a time elapsed between a transition of the trigger signal and a transition of the hit signal, wherein the digital value is a count of a number of transitions of a digital clock signal that occur between the transition of the trigger signal and the transition of the hit signal.
17. The method of claim 16 , further comprising:
generating (i) a first electrical signal indicative of a time difference between the transition of the hit signal and a subsequent transition of the digital clock signal and (ii) a second electrical signal indicative of a time difference between the transition of the hit signal and a subsequent transition of an inverse of the digital clock signal; and
generating a metastability signal, wherein the metastability signal is the digital clock signal shifted by half of a period of the digital clock signal.
18. The method of claim 17 , further comprising:
estimating a value of a time of flight of the measurement beam of illumination light based at least in part on the digital value indicative of the time elapsed between the transition of the trigger signal and the transition of the hit signal, the time difference between the transition of the hit signal and the subsequent transition of the digital clock signal, the time difference between the transition of the hit signal and the subsequent transition of the inverse of the digital clock signal, and the metastability signal.
19. The method of claim 16 , further comprising:
generating an electrical signal indicative of a time difference between a transition of an enable signal and a time when an amplitude of the hit signal falls below a threshold value.
20. The method of claim 16 , further comprising:
generating an amplitude signal indicative of a peak amplitude of the output signal after the transition of the hit signal.
21. The method of claim 20 , further comprising:
generating a plurality of output signal samples each indicative of a respective amplitude of the output signal before or after the peak amplitude, wherein a number of output signal samples before or after the peak amplitude is programmable.
22. The method of claim 15 , further comprising:
receiving, by the return signal receiver mounted to the printed circuit board, a command signal; and
generating, by the return signal receiver the trigger signal in response to receiving the command signal.
23. An integrated LIDAR measurement device, comprising:
a photodetector mounted to a substrate, the photodetector configured to detect (i) a first amount of a measurement beam of illumination light due to crosstalk between an illumination source and the photodetector and (ii) a return light signal reflected from a location in a surrounding environment illuminated by a second amount of the measurement beam; and
a return signal receiver mounted to a printed circuit board and configured to, in response to receiving a command signal, generate a trigger signal, and estimate a time between when the first amount of the measurement beam of illumination light due to the crosstalk is detected and when the return pulse of light signal is detected.
24. The integrated LIDAR measurement device of claim 23 , further comprising:
an illumination source mounted to the printed circuit board; and
an illumination driver mounted to the printed circuit board, the illumination driver IC configured to selectively couple the illumination source to an electrical power source in response to the trigger signal, to cause the illumination source to emit the measurement beam of illumination light.