CN112904313A

CN112904313A - Method, system, and electronic circuit for suppressing ambient light of LiDAR equipment

Info

Publication number: CN112904313A
Application number: CN202110106873.0A
Authority: CN
Inventors: 宋云鹏
Original assignee: Guangwei Technology Guangzhou Co ltd
Current assignee: Guangwei Technology Guangzhou Co ltd; Liturex Guangzhou Co Ltd
Priority date: 2021-01-26
Filing date: 2021-01-26
Publication date: 2021-06-04

Abstract

Systems and methods for suppressing ambient light on a photodetector of a LiDAR device are disclosed. The LiDAR device may be configured to scan the laser pulses in such a manner: the reflected laser pulses are incident on a column of macropixels in a macropixel array on the photodetector at a time, wherein only the macropixels of the column are turned on, and the macropixels of the remaining columns are turned off. The LiDAR device may be further configured to scan at different angles such that a laser pulse from the same portion of the target object may be incident on the turned-on column of macropixels multiple times to improve the resolution of the LiDAR image. In addition, the outputs from multiple SPADs in the largest pixel are cascaded to form a multi-level digital signal, and thresholds are employed to discard or register the multi-level digital signal to further reduce noise.

Description

Method, system, and electronic circuit for suppressing ambient light of LiDAR equipment

Technical Field

Embodiments of the present invention relate generally to remote sensing and, more particularly, to a method of suppressing ambient light by selectively turning off photodetector sections and signal triggering using multi-level digital signals.

Background

LiDAR devices may measure distance to an object in an environment by illuminating the object with a laser pulse and measuring the object reflected pulse. LiDAR equipment typically utilizes advanced optics and rotating components to create a wide field of view, but such implementations tend to be bulky and expensive. Solid state lidar sensors tend to be lower in cost, but are still larger in size.

Solid state LiDAR devices often use Single Photon Avalanche Diodes (SPADs) with high photon sensitivity. However, SPADs are also susceptible to ambient light. Conventionally, histogram combining may be employed to remove ambient light, thereby improving the signal-to-noise ratio, but this may require a large amount of illumination to generate a usable histogram. Thus, this method is inefficient.

Disclosure of Invention

In various embodiments, described herein is a system and method for suppressing ambient light on a photodetector of a LiDAR device. The LiDAR device may be configured to scan the laser pulses in such a manner: the reflected laser pulses are incident on a column of macropixels in a macropixel array on the photodetector at a time, wherein only the macropixels of the column are turned on, and the macropixels of the remaining columns are turned off. The LiDAR device may be further configured to scan at different angles such that a laser pulse from the same portion of the target object may be incident on the turned-on column of macropixels multiple times to improve the resolution of the LiDAR image. In addition, the outputs from multiple SPADs in the largest pixel are cascaded to form a multi-level digital signal, and thresholds are employed to discard or register the multi-level digital signal to further reduce noise. Also described herein is electronic circuitry that performs the method for suppressing ambient light on a photodetector of a LiDAR device.

Drawings

Embodiments of the present disclosure are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like reference numerals refer to similar elements.

FIG. 1 shows an example of LiDAR equipment in which method embodiments of the present invention may be implemented.

FIG. 2 illustrates a system for suppressing ambient light on a LiDAR photodetector, according to one embodiment.

3A-3B illustrate an example of a multi-level digital signal and an example of thresholds according to one embodiment.

FIG. 4 further illustrates a system for suppressing ambient light according to one embodiment.

FIG. 5 is a process of a method of suppressing ambient light in a LiDAR device according to one embodiment.

Detailed Description

The following description and drawings are illustrative and are not to be construed as limiting. Numerous specific details are described below to provide a thorough understanding of various embodiments. However, in certain instances, well-known or conventional details are not described in order to provide a concise discussion of the embodiments.

In various embodiments, described herein is a system and method for suppressing ambient light on a photodetector of a LiDAR device. The LiDAR device may be configured to scan the laser pulses in such a manner: the reflected laser pulses are incident on a column of macropixels in a macropixel array on the photodetector at a time, wherein only the macropixels of the column are turned on, and the macropixels of the remaining columns are turned off. The LiDAR device may be further configured to scan at different angles such that a laser pulse from the same portion of the target object may be incident on the turned-on column of macropixels multiple times to improve the resolution of the LiDAR image. In addition, the outputs from multiple SPADs in the largest pixel are cascaded to form a multi-level digital signal, and thresholds are employed to discard or register the multi-level digital signal to further reduce noise.

In one embodiment, a system for suppressing ambient light in a light detection and ranging (LiDAR) device includes a photodetector comprising a plurality of macropixels forming a macropixel array, each macropixel in the photodetector comprising a plurality of Single Photon Avalanche Diodes (SPADs); a laser scanner to scan laser beams in different directions; and a control unit configured to control the laser scanner to scan the laser beam such that the reflected laser photons are incident on a column of macro-pixels of the photodetector at a time, the column of macro-pixels being turned on, and macro-pixels on the remaining macro-photodetectors being turned off.

In one embodiment, the system further comprises a plurality of adders, each configured to read photons from each macropixel in the turned-on macropixel column and construct a multilevel digital signal. The photons read from the macropixel include one or more signal photons and one or more noise photons. The control unit is further configured to register the multi-level digital signal based on a predetermined threshold.

In one embodiment, the laser scanner is configured to scan a predetermined number of times at different angles at a time, such that the opened column of macropixels receive reflected laser pulses of the same portion of the target object from different angles. The laser scanner may also be configured to scan a predetermined number of times at the same angle each time, such that the opened column of macro-pixels receives reflected laser pulses of the same portion of the target object from different angles. The control unit is configured to construct a multi-level digital signal by using an adder or to read photons from an opened column of macropixels without using an adder.

In one embodiment, the laser beam is a linear laser beam that is diffused out of a laser spot by a diffuser in the LiDAR device or is directly generated by a laser pulse emitting unit in the LiDAR device.

Embodiments described herein may include a non-transitory machine-readable medium storing executable computer program instructions that, when executed by one or more data processing systems, may cause the one or more data processing systems to perform one or more of the methods described herein. The instructions may be stored in a non-volatile memory, such as a flash memory or other form of memory. Embodiments may also be implemented as a system.

The operation sequence of the method in the embodiment of the invention can be adjusted, and some operations can be combined or deleted according to actual needs.

The above summary does not include an exhaustive list of all embodiments in the present disclosure. All of the devices and methods in this disclosure can be practiced from all suitable combinations of the various aspects and embodiments described in this disclosure.

Solid state LiDAR device

FIG. 1 illustrates an example of LiDAR equipment in which embodiments of the method of the present invention may be implemented in accordance with one embodiment.

The LiDAR device may be a solid-state LiDAR device 101 that may measure a distance to an object in an environment by illuminating the object with a laser pulse (laser beam). The difference in the return time of the reflected laser pulse and the wavelength can be used to create a point cloud of the environment. The point cloud may provide spatial location and depth information for identifying and tracking objects.

As shown in FIG. 1, the LiDAR device 101 includes a laser pulse emitting unit 104, a laser pulse scanner 105, a laser pulse receiving unit 109, and a control unit 107. The laser pulse emitting unit 104 may include one or more laser emitters that may emit short-pulse laser beams containing photons of different frequencies. The laser pulse emitting unit may emit a laser spot or a linear laser beam. In some embodiments, a diffuser may be used to increase the size of the laser spot, including changing the shape of the laser spot to a laser beam.

In one embodiment, the laser pulse emitting unit 104 may emit a linear laser beam. In this embodiment, the laser pulse firing unit 104 uses a plurality of Fast Axis Collimators (FACs) to collimate laser beams from an array of laser sources, an array of cylindrical lenses to convert the collimated laser beams into parallel laser beams, and a pair of pitch prism arrays to reduce the parallel laser beams. The laser pulse emitting unit 104 may further include a first cylindrical lens for focusing the laser beam from the prism array pair onto a MEMS mirror that redirects the laser beam as a linear laser beam in a predetermined direction.

For example, in fig. 1, the laser pulse emission unit 104 emits an emission laser pulse beam 113. The outgoing laser pulse beam 113 may be steered or scanned by the laser pulse scanner 105 using various means, including micro-electromechanical system (MEMS) mirrors and one or more Optical Phased Arrays (OPAs), in one or more directions, each of which may be referred to as a steering direction or a scanning direction.

The control unit 107 may include control logic implemented in hardware, software, firmware, or a combination thereof. The control unit 107 may drive the other units or

subsystems

104, 105, and 109 of the LiDAR device 101 in a coordinated manner and may execute one or more data processing algorithms to perform one or more operations for signal filtering and target detection. For example, the control unit 107 may synchronize the laser pulse emitting unit 104 and the laser pulse scanner 105 so that the laser pulse scanner 105 can perform multi-line scanning of the horizontal field of view.

The laser pulse receiving unit 109 may collect one or more laser pulse beams (e.g., laser pulse beam 112) reflected from the target object 103 using one or more imaging lenses (e.g., imaging lens 115) and focus the laser pulse beams on one or more photodetectors (e.g., photodetector 117). The photodetector may comprise a plurality of high sensitivity photodiodes. The photodetector may convert photons in the reflected beam of laser pulses into electricity. The laser pulse receiving unit 109 may send the return signal incident on each photodetector to the control unit 107 for processing.

In one embodiment, the laser diodes in the laser pulse firing unit 104 may operate in a pulsed mode, where the pulses are repeated at fixed intervals (e.g., every few microseconds). The laser diode and laser drive circuitry used to provide the appropriate bias and modulation current for the laser diode may be selected according to predetermined performance parameters of the LiDAR device 101. Performance parameters may include, for example, the maximum scan spatial range and resolution required.

Ambient light suppression

FIG. 2 illustrates a system for suppressing ambient light on a photodetector of a LiDAR device, according to one embodiment.

As shown in fig. 2, the photodetector 117 includes a plurality of macro-pixels to form a macro-pixel array. As used herein, a macropixel is also referred to as a maximum pixel.

In fig. 2, the macro-pixel array may include 12 macro-pixels, each macro-pixel including 9 SPADs. The 12 macropixels are distributed among 3 rows of macropixels and 4 columns of

macropixels

220, 222, 224, and 225. The macropixels in each row are connected through and to a bus to which an adder is connected.

For example, the adder a213 is connected to a bus 220 connecting the first row macro-pixels, the adder B215 is connected to a bus connecting the second row macro-pixels, and the adder C is connected to a bus connecting the third row macro-pixels. All the macro-pixels in the photodetector 117 may be connected together by different buses or adders.

The laser pulse scanner unit 105 of the LiDAR device 101 may be controlled by the control unit 107 to scan the laser pulses in this manner: reflected laser pulses from the target object are incident on the macropixel array on the photodetector from left to right, one column of macropixels at a time. For example, a reflected laser pulse may be incident first on a column 220, then on B column 222, then on C column 224 and D column 226.

The control unit 107 may dynamically switch each column of macropixels on and off, depending on which column is to receive the reflected pulse. In one embodiment, the control unit 107 may only turn on the column of macropixels that is to receive the reflected laser pulses; and turns off the other macropixel columns on the photodetector 117.

By dynamically turning on and off columns of macropixels, the signal-to-noise ratio of LiDAR device 101 may be improved because the turned-off macropixels cannot receive any photons (including ambient photons). The turned off macropixel will not receive any photons due to the reflection of the illumination in the particular scan shown in fig. 2. Thus, if the macropixels are not turned off, any photons incident on these macropixels will be noise.

Fig. 2 shows that the a column 220 of macro-pixels is open and receiving a reflected signal. Thus, only the A column 220 is open, and the remaining columns (222, 224, and 226) are closed. However, at another point in time, when B column 222 receives a reflected laser signal from the corresponding scan angle, A column 220 will be closed, and C column 224 and D column 226 will remain closed. In the entire photodetector, only the B column 222 is turned on.

As further shown in fig. 2, each macropixel may receive one or more photons representative of the true signal reflected from the target object, as well as one or more noise photons. For example, macro-pixel 201 may receive

signal photons

217, 218, and 219; and noise photons 221 from ambient light. The control unit 107 or adder 1213 can convert all

photons

217, 218, 219, and 221 incident on the macro-pixel 201 into electrical signals. Since

photons

217, 218, 219, and 221 arrive at slightly different times, adder 1213 outputs a multi-level digital signal. In the embodiment shown in fig. 2, a four-level digital signal is formed from four photons received at the macropixel 201, including the noise photon 217.

In one embodiment, the control unit 107 may apply a predetermined threshold to the four-level digital signal. The threshold may be used to determine whether to register the four-level digital signal as a signal event or discard it as a noise event.

For example, the threshold may be set to 3.5. Since the number of stages representing the number of photons is equal to or greater than the threshold value, the control unit 107 can register the four-stage digital signal as a signal event.

Another macropixel 222 may receive two

noise photons

226 and 228 from ambient light and one signal photon 224. The three-level digital event constructed by the control unit 107 from the macropixel 222 will then be discarded as noise because the level is up to a threshold of 3.5.

In an alternative embodiment, the control unit 107 is configured to read photons from an open column of macropixels without using adders 213, 215, and 217 to construct the multilevel digital signal.

Fig. 3A illustrates a macro-pixel 201 and an adder a 213. The adder a213 may be part of the signal processing circuit or may be a separate circuit in the control unit 107. Summer A213 can count 4

photons

217 and 221 from a reflected laser pulse from a particular scan angle of the LiDAR device 101. The control unit 107 may control the laser pulse scanner 105 to scan at different angles at regular time intervals (e.g., every 600 nanoseconds). After a short delay (e.g., 100 nanoseconds) after each scan, photons from the scan angle are incident on the photodetector 117. Thus, the control unit 107 may calculate when a particular column of macro-pixels receives a reflected photon.

In this embodiment, the macropixel column 220 containing macropixels 201 will receive reflected photons. The control unit 107 may turn on the macropixel 220 of the column and turn off all other

macropixel columns

222, 224, and 226. Thus, the photodetector 117 expects received signal photons to be incident on the photodetector 117 in a time cluster that they arrive at approximately the same time, which means that the greater the number of photons received at a macropixel, the greater the probability that the photon will be a signal photon.

Thus, a threshold may be employed to determine which multi-level digital signal is a noise event and which is a signal event. For example, if a particular macropixel receives only one photon, that photon is likely to be a random noise photon, since the signal photon would be expected to be incident on the macropixel in a time cluster.

In one embodiment, a value of 3.5 for threshold 317 may be applied to multi-level digital signal 319 of 4 photons received from macropixel 201 by adder a 213. In this case, since the number of stages of the multilevel digital signal is equal to or exceeds the threshold value of 3.5, the adder a213 may register the multilevel digital signal as a signal event.

Fig. 3B illustrates a macropixel 222 and an adder B215. As shown in fig. 3B, the three-level digital signal 321 converted from photons incident on the macro-pixel 222 does not reach the threshold 317, and thus the control unit 107 treats it as a noise event.

FIG. 4 further illustrates a system for suppressing ambient light according to one embodiment. More specifically, the figure depicts features that may be used to compensate for the loss of resolution due to the use of macropixels in the photodetector 117 and the possible rejection of signal photons that may be identified as noise photons.

As described above, the photodetector 117 sets SPADs in macro-pixels, which results in fewer pixels than a photodetector that registers one pixel per SPAD. Furthermore, the use of a threshold may potentially result in some signal photons being discarded. The above factors may reduce the resolution of the LiDAR image.

In one embodiment, as shown in fig. 4, while macro-pixel column a220 is turned on to receive the reflected signal, the control unit 107 may control the laser pulse scanner 105 to scan at slightly different angles 401, 403, and 405, and each scan may result in reflected photons from the same portion of the target object being incident on column a 220.

For each scan, the control unit 107 may construct a multi-level digital signal for each macro-pixel in the a-column 220 using the adders 213, 215, and 214, and determine to register or discard the multi-level digital signal based on the number of levels thereof.

Each scan may yield additional information for the target object, and signal photons from all scans may be added together to improve the resolution of the LiDAR image.

In one embodiment, the different scans may be directed at the same angle. In this case, reflected laser pulses (reflected laser photons) from different scans are incident on the a column 220. Likewise, multiple scans of the same angle may also improve the resolution of the LiDAR image.

FIG. 5 illustrates a process 500 of a method of suppressing ambient light in a LiDAR device according to one embodiment. The process 500 may be performed by processing logic that may include software, hardware, firmware, or a combination thereof. This process 500 may be performed by the control unit 107 depicted in fig. 1, for example.

As shown in FIG. 5, in step 501, processing logic sends instructions to instruct a laser scanner of a LiDAR device to scan a laser beam at a particular angle. In step 503, processing logic turns on a column of macropixels on a photodetector of the LiDAR device, the photodetector including a plurality of macropixels forming a macropixel array, each macropixel in the photodetector including a plurality of Single Photon Avalanche Diodes (SPADs), and turns off remaining columns of macropixels on the photodetector. In step 505, processing logic reads reflected photons incident from a particular angle onto a column of macropixels on a photodetector of a LiDAR device.

Some or all of the components shown and described above may be implemented in software, hardware, or a combination thereof. For example, such components may be implemented as software installed and stored in a persistent storage device, which may be loaded into and executed in a memory by a processor (not shown) to perform the procedures or operations described throughout this application. Alternatively, such components may be implemented as executable code programmed or embedded into dedicated hardware, such as hardware (e.g., an integrated circuit (e.g., an application specific IC or ASIC), a Digital Signal Processor (DSP) or a Field Programmable Gate Array (FPGA)), accessible from application programs via corresponding drivers and/or operating systems. Further, such components may be implemented as specific hardware logic in a processor or processor core as part of an instruction set accessible by software components via one or more specific instructions.

Some portions of the detailed descriptions which follow are presented in terms of algorithms and symbolic representations of operations on data bits within a computer memory. These algorithmic descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of operations leading to a desired result. The operations are those requiring physical manipulations of physical quantities.

These and similar terms are to be associated with the corresponding physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the above discussion, it is appreciated that throughout the description, discussions utilizing terms such as those set forth in the following claims refer to the actions and processes of a computer system, or similar electronic computing device. The data represented as physical (electronic) quantities within the computer system's registers and memories are manipulated and transformed, and other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.

Embodiments of the present disclosure also relate to an apparatus for performing the operations herein. Such a computer program is stored in a non-transitory computer readable medium. A machine-readable medium includes any mechanism for storing information in a form readable by a machine (e.g., a computer). For example, a machine-readable (e.g., computer-readable) medium includes a machine (e.g., computer) readable storage medium (e.g., read only memory ("ROM"), random access memory ("RAM"), magnetic disk) storage medium, optical storage medium, flash memory device).

The processes or methods described in the above figures may be performed by processing logic that comprises hardware (e.g., circuitry, dedicated logic, etc.), software (e.g., embodied on a non-transitory computer readable medium), or a combination of both. Although the processes or methods described above are described in terms of some sequential operations, it should be noted that some of the operations described may be performed in a different order. Moreover, some operations may be performed in parallel, rather than sequentially.

Embodiments of the present disclosure are not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of embodiments of the disclosure as described herein.

In the foregoing specification, embodiments of the disclosure have been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications may be made thereto without departing from the broader spirit and scope of the disclosure as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.

Claims

1. A system for suppressing ambient light in a light detection and ranging (LiDAR) device, comprising:

a photodetector comprising a plurality of macropixels forming a macropixel array, each macropixel in the photodetector comprising a plurality of Single Photon Avalanche Diodes (SPADs);

a laser scanner to scan laser beams in different directions; and

a control unit configured to control the laser scanner to scan the laser beam such that reflected laser photons are incident on a column of macro-pixels of the photodetector at a time, wherein the column of macro-pixels is turned on and remaining macro-pixels on the photodetector are turned off.

2. The system of claim 1, further comprising:

a plurality of adders, each adder configured to read a photon from each macro-pixel in the column of macro-pixels that is turned on and to construct a multi-level digital signal.

3. The system of claim 2, wherein: the photons read out of the macropixel include one or more signal photons and one or more noise photons.

4. The system of claim 3, wherein: the control unit is further configured to register the multi-level digital signal based on a predetermined threshold.

5. The system of claim 1, wherein: the laser scanner is configured to scan a predetermined number of times at different angles each time such that the opened column of macropixels receives reflected laser pulses of the same portion of the target object from different angles.

6. The system of claim 1, wherein: the laser scanner is configured to perform a predetermined number of scans at the same angle each time such that the opened column of macropixels receives reflected laser pulses of the same portion of the target object from different angles.

7. The system of claim 1, wherein: the control unit is configured to read photons from the column of macropixels that is turned on without using an adder.

8. The system of claim 1, wherein: the laser beam is a linear laser beam that is diffused out of a laser spot by a diffuser in the LiDAR device or a linear laser beam that is directly generated by a laser pulse emitting unit in the LiDAR device.

9. A method for suppressing ambient light in a light detection and ranging (LiDAR) device, comprising:

sending instructions to instruct a laser scanner of the LiDAR device to scan a laser beam at a particular angle;

opening a largest column of pixels on a photodetector of the LiDAR device, the photodetector including a plurality of macropixels forming a macropixel array, each macropixel in the photodetector including a plurality of Single Photon Avalanche Diodes (SPADs), and turning off remaining columns of macropixels on the photodetector; and

reading a reflected photon incident on the largest pixel column on the photodetector of the LiDAR device from a particular angle.

10. The method of claim 9, further comprising:

photons are read from each of the macropixels in the column of macropixels that are turned on by each of a plurality of adders and a multilevel digital signal is constructed.

11. The method of claim 10, wherein: the photons read out of the macropixel include one or more signal photons and one or more noise photons.

12. The method of claim 11, further comprising: registering the multi-level digital signal based on a predetermined threshold.

13. The method of claim 9, further comprising: the scanning is performed a predetermined number of times at different angles each time so that the opened column of macropixels receives reflected laser pulses of the same portion of the target object from different angles.

14. The method of claim 9, further comprising: the scanning is performed a predetermined number of times at the same angle each time so that the opened column of macropixels receives reflected laser pulses of the same portion of the target object from different angles.

15. The method of claim 1, wherein: the control unit is configured to read photons from the column of macropixels without using an adder.

16. The method of claim 9, wherein the laser beam is a linear laser beam diffused out of a laser spot by a diffuser in the LiDAR device or a linear laser beam directly generated by a laser pulse emitting unit in the LiDAR device.

17. Electronic circuitry embedded in a light detection and ranging (LiDAR) device, the electronic circuitry configured to perform operations of:

18. The electronic circuit of claim 17, wherein the operations further comprise:

19. The electronic circuit of claim 18, wherein: the photons read out of the macropixel include one or more signal photons and one or more noise photons.

20. The electronic circuit of claim 19, wherein the operations further comprise: registering the multi-level digital signal based on a predetermined threshold.