Sizing the field of view of a detector to improve operation of a lidar system
A lidar system includes a light source, a scanner, and a receiver and is configured to detect remote targets located up to R MAX meters away. The receiver includes a detector with a field of view larger than the light-source field of view. The scanner causes the detector field of view to move relative to the instantaneous light-source field of view along the scan direction, so that (i) when a pulse of light is emitted, the instantaneous light-source field of view is approximately centered within the detector field of view, and (ii) when a scattered pulse of light returns from a target located R MAX meters away, the instantaneous light-source field of view is located near an edge of the field of view of the detector and is contained within the field of view of the detector.
1. A lidar system comprising:
a light source configured to emit pulses of light along a light-source field of view (FOV);
a scanner configured to scan the light-source FOV across a field of regard (FOR) of the lidar system and direct the pulses of light along a forward scan direction and subsequently along a reverse scan direction, wherein each of the pulses of light illuminates a respective instantaneous light-source FOV which corresponds to the light-source FOV at a time when the pulse of light is emitted; and
a receiver configured to detect the pulses of light scattered by one or more targets, the receiver including a detector, comprising three or more detector elements arranged with a first high gain detector element adjacent to a low gain detector element adjacent to a second high gain detector element, with a detector FOV that corresponds to an angular region over which the detector is configured to receive scattered light, wherein the detector includes an avalanche photodiode (APD) configured to produce an electrical-current pulse corresponding to the scattered light from the first pulse of light, wherein the APD comprises a transparent electrode configured to transmit the first pulse of light to an active region of the APD, wherein:
the lidar system is configured to detect the one or more targets, wherein the one or more targets are located up to R MAX meters away from the lidar system, and
the scanner causes the detector FOV to move relative to the instantaneous light-source FOV along each of the scan directions so that an amount of overlap between an instantaneous light-source FOV associated with a first pulse of light and the detector FOV is different at two or more instances of time in an interval between (i) when the first pulse of light is emitted and (ii) when scattered light from the first pulse of light returns from a first target of the one or more targets, the first target located R MAX meters away.
2. The lidar system of claim 1 , wherein the scanner causes the detector FOV to have less than or equal to 20% overlap with the instantaneous light-source FOV when the first pulse of light is emitted.
3. The lidar system of claim 1 , wherein the scanner causes the detector FOV to partially, but not fully, overlap with an instantaneous light-source FOV associated with a second emitted pulse of light during a time interval between (i) when the second pulse of light is emitted and (ii) before scattered light from the second pulse of light returns from a second target of the one or more targets, the second target located less than M meters away, wherein M is less than R MAX .
4. The lidar system of claim 3 , wherein the scanner causes an instantaneous light-source FOV associated with a third emitted pulse of light to be fully contained within the detector FOV during a time interval between (i) when scattered light from the third pulse of light can return from the second target located less than M meters away and (ii) before scattered light from the third pulse of light can return from the first target located R MAX meters away.
5. The lidar system of claim 3 , wherein the lidar system is configured to deactivate or reduce a gain of the receiver during the time interval between (i) when the second pulse of light is emitted and (ii) before the scattered light from the second pulse of light returns from the second target.
6. The lidar system of claim 1 , wherein the scanner causes an instantaneous light-source FOV associated with a subsequently emitted pulse of light to be at least partially outside the detector FOV when scattered light from the subsequent pulse of light returns from a target located more than R MAX meters away.
7. The lidar system of claim 1 , wherein the light-source FOV is smaller than the detector FOV.
8. The lidar system of claim 1 , wherein the scanner is configured to direct the pulses of light along each of the scan directions to produce a plurality of scan lines distributed in a nonuniform manner across the FOR of the lidar system, wherein scan lines located near a periphery of the FOR are farther apart as compared to scan lines located near a center of the FOR.
9. The lidar system of claim 1 , wherein the scanner is configured to scan the light-source FOV and the detector FOV in a synchronous manner, wherein the light-source FOV and the detector FOV are scanned along each of the scan directions at equal scan speeds while maintaining a same relative position to each other.
10. The lidar system of claim 1 , wherein R MAX is a maximum range of the lidar system, corresponding to a maximum distance over which the lidar system is configured to detect the pulses of light scattered by the one or more targets located up to R MAX meters away from the lidar system.
11. The lidar system of claim 1 , wherein the receiver further includes a lens that focuses received scattered light onto an active region of the detector.
12. The lidar system of claim 1 , wherein the receiver further includes a pulse-detection circuit coupled to the APD, the pulse-detection circuit comprising:
a transimpedance amplifier (TIA) configured to receive the electrical-current pulse from the APD and produce a voltage pulse that corresponds to the received electrical-current pulse;
a gain circuit configured to amplify the voltage pulse;
a comparator configured to produce an electrical-edge signal when the amplified voltage pulse rises above or falls below a particular threshold voltage; and
a time-to-digital converter (TDC) configured to determine an interval of time between emission of the first pulse of light and receipt of the electrical-edge signal.
13. The lidar system of claim 1 , wherein the APD is an Indium Gallium Arsenide (InGaAs) APD.
14. The lidar system of claim 1 , wherein the low gain detector element is smaller in size than both of the high gain detector elements.
15. The lidar system of claim 1 , wherein each of the detector elements is approximately the same size.
16. The lidar system of claim 1 , wherein the low gain detector element partially overlaps at least one of the high gain detector elements.
17. The lidar system of claim 1 , wherein the gain of each of the detector elements is related to a surface area, detector type, field of view, physical or chemical properties, or associated circuitry, of the respective detector element.
18. The lidar system of claim 1 , wherein the low gain detector element is used to shield at least one of the high gain detector elements from an early return pulse.
19. The lidar system of claim 1 , wherein each of the detector elements is either circular, square or rectangular.
20. A method in a lidar system for scanning a field of regard (FOR) of the lidar system, the lidar system configured to detect one or more targets located up to R MAX meters away from the lidar system, the method comprising:
emitting, by a light source of the lidar system, pulses of light along a light-source field of view (FOV);
scanning, by a scanner of the lidar system, the light-source FOV across the FOR of the lidar system, comprising directing the pulses of light along a forward scan direction and subsequently along a reverse scan direction, wherein each of the pulses of light illuminates a respective instantaneous light-source FOV which corresponds to the light-source FOV at a time when the pulse of light is emitted;
detecting, by a receiver of the lidar system, the pulses of light scattered by the one or more targets, the receiver including a detector, comprising three or more detector elements arranged with a first high gain detector element adjacent to a low gain detector element adjacent to a second high gain detector element, with a detector FOV that corresponds to an angular region over which the detector is configured to receive scattered light, the detector including an avalanche photodiode (APD) configured to produce an electrical-current pulse corresponding to the scattered light from the first pulse of light and the APD comprising a transparent electrode configured to transmit the first pulse of light to an active region of the APD; and
causing, by the scanner, the detector FOV to move relative to the instantaneous light-source FOV along each of the scan directions so that an amount of overlap between an instantaneous light-source FOV associated with a first pulse of light and the detector FOV is different at two or more instances of time in an interval between (i) when the first pulse of light is emitted and (ii) when scattered light from the first pulse of light returns from a first target of the one or more targets, the first target located R MAX meters away.
21. The method of claim 20 , further comprising causing the detector FOV to have less than or equal to 20% overlap with the instantaneous light-source FOV when the first pulse of light is emitted.
22. The method of claim 20 , further comprising causing the detector FOV to partially, but not fully, overlap with an instantaneous light-source FOV associated with a second emitted pulse of light during a time interval between (i) when the second pulse of light is emitted and (ii) before scattered light from the second pulse of light returns from a second target of the one or more targets, the second target located less than M meters away, wherein M is less than R MAX .
23. The method of claim 22 , further comprising causing an instantaneous light-source FOV associated with a third emitted pulse of light to be fully contained within the detector FOV during a time interval between (i) when scattered light from the third pulse of light can return from the second target located less than M meters away and (ii) before scattered light from the third pulse of light can return from the first target located R MAX meters away.
24. The method of claim 22 , further comprising deactivating or reducing a gain of the receiver during the time interval between (i) when the second pulse of light is emitted and (ii) before the scattered light from the second pulse of light returns from the second target.
25. The method of claim 20 , further comprising directing the pulses of light along each of the scan directions to produce a plurality of scan lines distributed in a nonuniform manner across the FOR of the lidar system, wherein scan lines located near a periphery of the FOR are farther apart as compared to scan lines located near a center of the FOR.
26. The method of claim 20 , further comprising scanning the light-source FOV and the detector FOV in a synchronous manner, wherein the light-source FOV and the detector FOV are scanned along each of the scan directions at equal scan speeds while maintaining a same relative position to each other.
27. The method of claim 20 , wherein the low gain detector element is smaller in size than both of the high gain detector elements.
28. The method of claim 20 , wherein each of the detector elements is approximately the same size.
29. The method of claim 20 , wherein the low gain detector element partially overlaps at least one of the high gain detector elements.
30. The method of claim 20 , wherein the gain of each of the detector elements is related to a surface area, detector type, field of view, physical or chemical properties, or associated circuitry, of the respective detector element.
31. The method of claim 20 , wherein the low gain detector element is used to shield at least one of the high gain detector elements from an early return pulse.
32. The method of claim 20 , wherein each of the detector elements is either circular, square or rectangular.