Adaptive Ladar Receiver

• US 20170242106A1
• Filed: 02/10/2017
• Published: 08/24/2017
• Est. Priority Date: 02/18/2016
• Status: Active Grant

• Current Assignee: AEye, Inc.
• Original Assignee: AEye, Inc.
• Inventors: Dussan, Luis Carlos, Steinhardt, Allan, Cook, David
• Granted Patent: US 10,754,015 B2
• Time in Patent Office: Days
• CPC Class Codes: G01S 17/08 for measuring distance only indirect measurement G01S17/46; active triangulation systems G01S17/48
• CPC Class Codes: G01S 17/10 using transmission of interrupted, pulse-modulated waves determination of distance by phase measurements G01S17/32
• CPC Class Codes: G01S 17/26 wherein the transmitted pulses use a frequency-modulated or phase-modulated carrier wave, e.g. for pulse compression of received signals
• CPC Class Codes: G01S 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 17/66 Tracking systems using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 17/931 of land vehicles
• CPC Class Codes: G01S 7/4813 Housing arrangements
• CPC Class Codes: G01S 7/4814 of transmitters alone
• CPC Class Codes: G01S 7/4815 using multiple transmitters
• CPC Class Codes: G01S 7/4816 of receivers alone
• CPC Class Codes: G01S 7/4817 relating to scanning
• CPC Class Codes: G01S 7/4818 using optical fibres
• CPC Class Codes: G01S 7/4863 Detector arrays, e.g. charge-transfer gates
• CPC Class Codes: G01S 7/4865 Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak peak detection in noise, signal conditioning G01S7/487
• CPC Class Codes: G01S 7/487 Extracting wanted echo signals , e.g. pulse detection
• CPC Class Codes: G01S 7/4876 by removing unwanted signals G01S7/495 takes precedence
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating

Abstract

Disclosed herein are various embodiment of an adaptive ladar receiver and associated method whereby the active pixels in a photodetector array used for reception of ladar pulse returns can be adaptively controlled based at least in part on where the ladar pulses were targeted. Additional embodiments disclose improved imaging optics for use by the receiver and further adaptive control techniques for selecting which pixels of the photodetector array are used for sensing incident light.

Claims

1. A ladar receiver apparatus comprising:

an array comprising a plurality of light sensors, each light sensor configured to sense light that is indicative of a plurality of ladar pulses reflected from a plurality of range points and generate a signal indicative of the sensed light; and

a circuit in communication with the array, the circuit configured to (1) selectively define a plurality of subsets of the light sensors for read out at a given time to produce a signal representative of the sensed light, the produced signal for use in computing range information with respect to the range points.

2. The apparatus of claim 1 wherein the circuit comprises:

a signal processing circuit; and

a multiplexer in communication with the array and the signal processing circuit, wherein the multiplexer is configured to selectively connect each defined subset of the light sensors with the signal processing circuit in response to a control signal such that the multiplexer passes the signal generated by each selectively connected light sensor to the signal processing circuit;

wherein the signal processing circuit is configured to amplify and convert the provided signals into a plurality of digital samples for processing to compute the range information with respect to the range points.

3. The apparatus of claim 2 wherein the circuit further comprises:

a control circuit in communication with the multiplexer, the control circuit configured to generate the control signal such that the control signal selects subsets of light sensors within the array based on locations of the range points in a field of view of a scanning ladar transmitter that transmits ladar pulses toward the range points.

4. The apparatus of claim 3 wherein the control circuit is further configured to generate the control signal such that the control signal selects subsets of light sensors within the array in a sequence that follows a shot list for the scanning ladar transmitter.

5. The apparatus of claim 3 wherein the shot list selectively targets a subset of range points within a field of view of the ladar transmitter.

6. The apparatus of claim 3 wherein the circuit further comprises:

a feedback circuit that provides a plurality of feedback signals to the light sensors for adjusting outputs from the light sensors.

7. The apparatus of claim 6 wherein the feedback circuit comprises a plurality of amplifiers between the light sensors and the multiplexer that amplify the outputs from the light sensors in a controlled feedback loop.

8. The apparatus of claim 7 further comprising a gain controller configured to control the amplifiers to produce a feedback gain that increases a signal to noise ratio for the outputs from the light sensors.

9. The apparatus of claim 7 wherein the feedback circuit is configured as a matching network feedback loop.

10. The apparatus of claim 6 wherein the ladar pulses comprise a plurality of ladar pulses that exhibit a Gaussian pulse shape.

11. The apparatus of claim 2 wherein the signal processing circuit includes a single channel for the signal passed by the multiplexer.

12. The apparatus of claim 2 wherein the signal processing circuit includes a plurality of channels for the signal passed by the multiplexer, and wherein the signal processing circuit is configured to reduce a noise component of the signal passed by the multiplexer based on signals present in the plurality of channels.

13. The apparatus of claim 12 wherein the signal processing circuit comprises a coherent combination circuit for the plurality of channels that includes a filter for reducing a spatially directional noise component of the signal passed by the multiplexer.

14. The apparatus of claim 2 wherein the subset comprises a plurality of the light sensors, wherein circuits are positioned to combine signals from a plurality of light sensors to each of a plurality of multiplexer input lines to thereby define composite pixels for readout to the signal processing circuit.

15. The apparatus of claim 2 wherein the signal processing circuit comprises an amplifier configured to amplify the provided signals.

16. The apparatus of claim 15 wherein the signal processing circuit further comprises an analog-to-digital converter (ADC) circuit downstream from the amplifier, the ADC circuit configured to convert the provided signals into the digital samples.

17. The apparatus of claim 15 wherein the signal processing circuit further comprises a time-to-digital converter (TDC) circuit downstream from the amplifier, the TDC circuit configured to convert the provided signals into the digital samples.

18. The apparatus of claim 2 wherein the signal processing circuit comprises a field programmable gate array (FPGA), the FPGA configured to compute the range information based on the digital samples.

19. The apparatus of claim 18 wherein the FPGA is further configured to perform interpolation on the digital samples to compute the range information.

20. The apparatus of claim 1 wherein the light sensors of the array correspond to a plurality of pixels, and wherein the subsets of selected light sensors change over time with respect to how many pixels are included in the subsets.

21. The apparatus of claim 1 wherein the light sensors of the array correspond to a plurality of pixels, and wherein a plurality of the pixels exhibit a hexagonal shape.

22. The apparatus of claim 21 wherein a plurality of the pixels exhibit different sizes.

23. The apparatus of claim 1 wherein a plurality of the pixels exhibit different sizes.

24. The apparatus of claim 1 further comprising a photodetector that is positioned optically downstream from the scanning ladar transmitter, wherein the photodetector comprises a region that is positioned to receive (1) the ladar pulses from the scanning ladar transmitter, and (2) light from the scanning ladar transmitter that is at a different frequency than the ladar pulses, and wherein the region is configured to pass the ladar pulses but absorb and convert the light at the different frequency into an output signal;

and

wherein the circuit is further configured to track where the scanning ladar transmitter is targeted based on the output signal from the photodetector.

25. The apparatus of claim 24 wherein the circuit is further configured to selectively define the subsets of light sensors based on the tracking of where the scanning ladar transmitter is targeted when ladar pulses are transmitted.

26. The apparatus of claim 1 wherein the array is further positioned to receive, via an optical path that is distinct from an optical path traveled by the ladar pulses from the scanning ladar transmitter to the array, a reference light from the scanning ladar transmitter for timing coordination with respect to the ladar pulses such that the produced signal includes a portion attributable to a reflected ladar pulse and a portion attributable to the reference light;

and

wherein the circuit is further configured to determine a timing relationship between the reflected ladar pulse and the reference light based on the produced signal.

27. The apparatus of claim 26 wherein the circuit is further configured to compute the range information for a range point corresponding to the reflected ladar pulse based on the determined timing relationship.

28. The apparatus of claim 26 wherein the reference light and the transmitted ladar pulses share a common pulse shape, and wherein the circuit is further configured to determine the timing relationship based on a correlation between a delayed version of the produced signal against the produced signal.

29. The apparatus of claim 28 wherein circuit is further configured to interpolate at least one of the delayed version of the produced signal and the produced signal to facilitate the timing relationship determination.

30. The apparatus of claim 28 wherein the distinct optical path comprises a direct optical path between the scanning ladar transmitter and the array.

31. The method of claim 28 wherein the reference light and the transmitted ladar pulses are the same pulse.

32. The apparatus of claim 1 wherein the ladar pulses comprise a plurality of ladar pulses that exhibit a Gaussian pulse shape.

33. The apparatus of claim 1 wherein the light sensors of the array correspond to a plurality of pixels, and wherein the circuit is configured to adapt which pixels are included in the defined subsets based on a detection of malfunctioning pixels such that pixels detected as malfunctioning are not included in the defined subsets.

34. The apparatus of claim 33 wherein the circuit is further configured to detect pixels that are malfunctioning.

35. The apparatus of claim 33 wherein the malfunctioning pixels comprise dark pixels.

36. The apparatus of claim 33 wherein the malfunctioning pixels comprise white pixels.

37. The apparatus of claim 1 wherein the light sensors of the array correspond to a plurality of pixels, and wherein the circuit is configured to adapt which pixels are included in the defined subsets based on a detection of an oversaturation condition to adjust a dynamic range for the produced signal in a manner that reduces the oversaturation condition.

38. The apparatus of claim 37 wherein the circuit is further configured to detect whether there is an oversaturation condition present with respect to the light sensed by the subset of pixels.

39. The apparatus of claim 37 wherein the oversaturation condition corresponds to an oversaturated pixel in the subset.

40. The apparatus of claim 37 wherein the subset comprises a plurality of pixels, and wherein the oversaturation condition corresponds to an aggregation of pixels in the produced signal.

41. The apparatus of claim 1 wherein the light sensors of the array correspond to a plurality of pixels, wherein the subset comprises a plurality of pixels, and wherein the circuit is configured to adapt which pixels are included in the defined subsets based on a detection of a pixel that is overly saturated with interfering light such that the overly saturated pixel is not included in the defined subsets while it is overly saturated with noise from interfering light.

42. The apparatus of claim 41 wherein the circuit is further configured to detect whether any pixels in the subset are overly saturated with noise from interfering light.

43. The apparatus of claim 41 wherein the interfering light corresponds to a ladar pulse from a different ladar transmitter.

44. The apparatus of claim 1 wherein the light sensors of the array correspond to a plurality of pixels, and wherein the circuit is configured to adapt which pixels are included in the defined subsets based on a detection of a scattered ladar pulse reflection.

45. The apparatus of claim 1 wherein the ladar receiver apparatus is part of a ladar system, the ladar system further comprising the scanning ladar transmitter;

and

wherein the scanning ladar transmitter is configured to adjust a shot list of range points based on feedback from the ladar receiver apparatus.

46. The apparatus of claim 45 wherein the adjusted shot list avoids range points that correspond to overly saturated pixels in the array.

47. The apparatus of claim 45 wherein the adjusted shot list avoids range points that correspond to a region of the field of view that includes too much interfering light.

48. The apparatus of claim 1 wherein the ladar receiver apparatus is part of a ladar system, the ladar system further comprising the scanning ladar transmitter;

and

wherein the scanning ladar transmitter is configured to adjust how much power is included in the ladar pulses based on feedback from the ladar receiver apparatus.

49. The apparatus of claim 1 further comprising:

a light collector in optical communication with the array, the light collector positioned to collect light onto the array.

50. The apparatus of claim 49 wherein the light collector comprises a fiber taper collector.

51. The apparatus of claim 50 wherein the fiber taper collector comprises a coherent fiber taper collector.

52. The apparatus of claim 49 further comprising a lens that includes an imaging system, wherein the lens is in optical communication with the light collector and configured to image light at an entrance pupil of the light collector.

53. The apparatus of claim 1 further comprising a lens that includes an imaging system, wherein the lens is in optical communication with the array and configured to image light onto the array.

54. The apparatus of claim 53 wherein the apparatus does not include a light collector between the lens and the array.

55. The apparatus of claim 1 wherein the ladar receiver apparatus is part of a ladar system, the ladar system further comprising the scanning ladar transmitter;

and

wherein the circuit is further configured to (1) process a signal indicative of the ladar system being in motion, and (2) reduce a noise component of the produced signal based on the processed motion-indicative signal.

56. An apparatus comprising:

a ladar receiver that includes a multi-pixel light sensor and a read out integrated circuit (ROIC) configured to read out signals sensed by each of a plurality of the pixels and process the read out signals, wherein the ROIC includes a multiplexer configured to selectively switch between the pixels for sensed signal read out.

57. The apparatus of claim 56 wherein the pixels comprise composite pixels.

58. A system comprising:

a ladar transmitter comprising a plurality of scanable mirrors, the ladar transmitter configured to (1) for each of a plurality of frames, select a subset of range points within a frame per frame, (2) selectively scan the scanable mirrors to target the selected range points for each frame, and (3) transmit a plurality of ladar pulses toward the targeted range points via the scanned mirrors; and

a ladar receiver comprising;

an array comprising a plurality of light sensors, each light sensor configured to sense light that is indicative of a plurality of ladar pulses reflected from the targeted range points and generate a signal indicative of the sensed light;

a signal processing circuit; and

a multiplexer in communication with the array and the signal processing circuit, wherein the multiplexer is configured to selectively connect a plurality of the light sensors with the signal processing circuit in response to a control signal such that the multiplexer passes the signal generated by each selectively connected light sensor to the signal processing circuit;

wherein the signal processing circuit is configured to amplify and convert the provided signals into a plurality of digital samples for processing to compute range information with respect to the targeted range points.