Frequency chirp for lidar for high-velocity targets
A device includes a controller with a processor and memory with instructions for controlling power to a light source such that the light source emits a frequency-modulated continuous light beam that, over time, includes an up region, a down region, and a flat region. The up region includes increasing a frequency of the continuous light beam, the down region includes decreasing the frequency of the continuous light beam, and the flat region includes maintaining the frequency of the continuous light beam at a constant frequency.
1. A method comprising:
emitting a frequency-modulated continuous light beam that, over time, includes an up region, a down region, and a flat region, wherein the up region includes increasing a frequency of the continuous light beam, the down region includes decreasing the frequency of the continuous light beam, and the flat region includes maintaining the frequency of the continuous light beam at a constant frequency;
detecting backscattered light;
determining a magnitude of a Doppler frequency shift based only on the detected backscattered light responsive to the flat region and not based on the detected backscattered light responsive to the up region and the down region; and
determining, based at least in part on the determined magnitude of the Doppler frequency shift, a velocity of a target.
2. The method of claim 1 , wherein the frequency during the up region increases linearly, wherein the frequency during the down region decreases linearly.
3. The method of claim 1 , wherein the up region lasts for a first period of time, the down region lasts for a second period of time, and the flat region lasts for a third period of time, wherein the third period of time is equal to or shorter than either of the first period of time or the second period of time.
4. The method of claim 1 , wherein the up region lasts for a first period of time, the down region lasts for a second period of time, and the flat region lasts for a third period of time, further comprising:
changing the length of the third period of time in response to detecting an event.
5. The method of claim 4 , wherein the event is recognizing the target.
6. The method of claim 1 , wherein the up region, the down region, and the flat region are repeated over time.
7. The method of claim 1 , wherein the up region, the down region, and the flat region create a first cycle, wherein a second cycle comprises a longer up region and a longer down region, further comprising:
emitting the frequency-modulated continuous light beam according to the first cycle; and
emitting the frequency-modulated continuous light beam according to the second cycle in response to recognizing the target.
8. The method of claim 1 , further comprising:
determining a slope of calculated frequency differences plotted along ramp rate; and
determining that at least one of the calculated frequency differences falls along the determined slope;
determining that another of the calculated frequency differences does not fall along the determined slope; and
determining, based only on the calculated frequency differences that fall along the determined slope, the velocity of the target.
9. A system comprising:
a light source controlled to emit a frequency-modulated continuous light beam that, over time, includes an up region, a down region, and a flat region, wherein the up region includes increasing a frequency of the continuous light beam, the down region includes decreasing the frequency of the continuous light beam, and the flat region includes maintaining the frequency of the continuous light beam at a constant frequency;
an optical detector arranged to detect backscattered light response to the up region, the down region, and the flat region; and
circuitry configured to:
determine a magnitude of a Doppler frequency shift based only on the detected backscattered light responsive to the flat region and not based on the detected backscattered light responsive to the up region and the down region,
determine that the magnitude of the Doppler frequency shift is greater than or less than a range frequency shift, and
determine a velocity of a target, based at least in part on the determined magnitude and that the magnitude is greater than or less than the range frequency shift.
10. The system of claim 9 , wherein the light source and the optical detector are packaged in a shared housing.
11. The system of claim 9 , further comprising:
a light steering device arranged to steer the continuous light beam along a pattern.
12. The system of claim 11 , wherein the light steering device is a mechanical device or solid-state device.
13. The system of claim 9 , further comprising:
a light source driver coupled to the light source and configured to apply a power signal to modulate the frequency of the emitted light of the light source.
14. A device comprising:
a controller including a processor and memory with instructions for controlling power to a light source such that the light source emits a frequency-modulated continuous light beam that, over time, includes an up region, a down region, and a flat region, wherein the up region includes increasing a frequency of the continuous light beam, the down region includes decreasing the frequency of the continuous light beam, and the flat region includes maintaining the frequency of the continuous light beam at a constant frequency,
wherein the memory of the controller further stores instructions for:
determining, based only on backscattered light responsive to the flat region and not based on the detected backscattered light responsive to the up region and the down region, that a Doppler frequency shift is greater than or less than a range frequency shift, and
determining a velocity of a target, based at least in part on whether the Doppler frequency shift is determined to be greater than or less than the range frequency shift.
15. The device of claim 14 , further comprising:
a light source driver operably coupled to the controller and the light source for providing power to the light source.
16. The device of claim 15 , further comprising:
the light source operably coupled to the light source driver and the controller.
17. The system of claim 9 , wherein a frequency range of the up region and the down region is 5-15 gigahertz.
18. The system of claim 17 , wherein the flat region lasts for 2 microseconds.
19. The system of claim 9 , wherein a length of time for the flat region is modified in response to detecting an event.
20. The method of claim 1 , further comprising:
determining that the magnitude of the Doppler frequency shift is greater than or less than a range frequency shift; and
determining the velocity of the target based further on the determining that the magnitude is greater than or less than the range frequency shift.