CN116324508A

CN116324508A - Dynamic receiver gain control for lidar systems

Info

Publication number: CN116324508A
Application number: CN202180070882.7A
Authority: CN
Inventors: 吕越; 维普·乔拉; 王佑民
Original assignee: Beijing Voyager Technology Co Ltd
Current assignee: Guangzhou Woya Lailing Technology Co ltd
Priority date: 2020-08-17
Filing date: 2021-07-20
Publication date: 2023-06-23
Also published as: WO2022039871A1

Abstract

Embodiments of the present specification provide an optical sensing system, a method for controlling a receiver gain in an optical sensing system, and a receiver in an optical sensing system. An exemplary optical sensing system includes an emitter configured to emit a light beam at a plurality of perpendicular detection angles to scan an object. The optical sensing system also includes a receiver having a detector configured to detect the beam returned by the object. The optical sensing system further includes a controller configured to dynamically vary the gain of the detector for detecting the light beam at each vertical detection angle.

Description

Dynamic receiver gain control for lidar systems

Cross reference

The present application claims priority from U.S. patent application Ser. No. 16/995,423, entitled "dynamic receiver gain control for lidar System", filed 8/17/2020, which is a continuation of U.S. patent application Ser. No. 16/920,650, entitled "dynamic laser Power control for lidar System", filed 7/3/2020, the contents of which are incorporated herein by reference.

Technical Field

The present specification relates to gain control for light detection and ranging (lidar) systems, and more particularly to dynamically controlling receiver gain to compensate for variations in detection distance of a lidar system at different perpendicular detection angles.

Background

Optical sensing systems such as lidar systems have been widely used in advanced navigation technologies, for example, to assist in autopilot or to generate high definition maps. For example, typical lidar systems measure distance to an object by illuminating the object with a pulsed laser beam and measuring reflected pulses with a sensor (e.g., a detector or detector array). The differences in laser return time, wavelength, and/or phase may then be used to construct a digital three-dimensional (3D) representation of the target. The laser radar system is particularly suitable for applications such as autopilot sensing and high definition map surveying, since physical features can be mapped with very high resolution using a narrow laser beam as incident light.

The pulsed laser beam emitted by the lidar system is typically directed in multiple directions to cover the field of view (FOV). For example, the vertical detection angle of a lidar system (referred to as the look-down angle when the scanning laser beam is directed downward) may be changed to scan objects in vertical space. The required detection distance varies with the vertical detection angle. For example, when the depression angle is small, that is, the lidar emits the scanning laser beam almost horizontally, the distance toward the object is long. On the other hand, as the depression increases, the distance toward the ground is shorter.

The laser beam reflected by a shorter distance (e.g., near the ground) object may carry higher power. However, conventional lidar systems use constant receiver gain for different vertical detection angles. Thus, a laser beam reflected from a shorter distance may cause the receiver to saturate. Receiver saturation can impair the accuracy of its distance and intensity measurements and cause other problems, such as overheating and instability of the receiver.

The present description embodiments improve performance of optical sensing systems, such as lidar systems, by implementing dynamic receiver gain control to compensate for variations in detection distance at different vertical detection angles of the sensing system.

Disclosure of Invention

Embodiments of the present disclosure provide an optical sensing system. An exemplary optical sensing system includes an emitter configured to emit a light beam at a plurality of perpendicular detection angles to scan an object. The optical sensing system further includes a receiver having a detector configured to detect the beam returned by the object. The optical sensing system further includes a controller configured to dynamically vary the gain of the detector for detecting the light beam at each vertical detection angle.

The present description embodiments also provide a method for controlling receiver gain in an optical sensing system. The method includes transmitting, by an emitter, a light beam at a plurality of perpendicular detection angles to scan an object. The method further comprises detecting the beam returned by the object by a detector in the receiver. The method further includes dynamically changing, by a controller, a gain of the detector for detecting the light beam at each vertical detection angle.

Embodiments of the present specification further provide a receiver in an optical sensing system. The receiver includes a detector configured to detect a beam returned by an object scanned by an emitted beam at a plurality of perpendicular detection angles. The receiver also includes a controller configured to dynamically change the gain of the detector based on a predetermined lookup table mapping each vertical detection angle to a target detector gain. The target detector gain is proportional to the square of the detection distance, which is determined based on the elevation angle and the corresponding vertical detection angle of the optical sensing system located above the ground.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

Drawings

Fig. 1 is a schematic diagram of an exemplary vehicle equipped with a lidar system according to an embodiment of the present description.

Fig. 2 is a block diagram of an exemplary lidar system according to an embodiment of the present description.

Fig. 3 is a schematic diagram of an exemplary detector in a receiver of a lidar system according to an embodiment of the present description.

Fig. 4 is a schematic diagram of an exemplary controller for adjusting the receiver gain of a lidar system according to an embodiment of the present description.

Fig. 5 is a view of a vertical detection angle and corresponding detection distance used during lidar scanning, as shown in an embodiment of the present disclosure.

Fig. 6 is a flow chart of an exemplary open loop control method for adjusting the receiver gain of a lidar system according to an embodiment of the present description.

Fig. 7 is a flow chart of an exemplary closed loop control method for adjusting the receiver gain of a lidar system according to an embodiment of the present description.

Detailed Description

Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

The present description embodiments provide systems and methods for dynamically controlling receiver gain in an optical sensing system (e.g., a lidar system). For example, the optical sensing system may include an emitter configured to emit a light beam (e.g., a laser beam) at a plurality of perpendicular detection angles to scan the object. The vertical detection angle is smaller, the detection distance is longer, and the vertical detection angle is larger and the detection distance is shorter. The emitted light beam is reflected from the scanned object and returned to and received by a receiver of the optical sensing system. For example, the receiver may comprise a detector that detects the return beam.

In some embodiments, the optical sensing system includes a controller configured to dynamically vary the gain of the detector for receiving the light beam emitted at each vertical detection angle. For example, the detector gain may be adjusted according to the detection distance at each vertical detection angle, since the beam returning from a shorter detection distance carries a higher laser power, thereby ensuring that a lower gain is used. In some embodiments, the detector gain may vary in proportion to the square of the detection distance. In some further embodiments, the detector gain may be further adjusted by the ratio of the reflectivity of the object to the reflectivity of the ground. As another example, the controller may determine the threshold angle based on an elevation angle of the optical sensing system above the ground and a threshold detection distance of the optical sensing system. Then, the controller decreases the detector gain when the vertical detection angle exceeds the threshold angle.

In some embodiments, the detector may further include a photodetector, a signal amplifier, and a signal conditioning circuit, and the gain of the detector may be varied by adjusting the gain of one or more of these individual components. For example, the controller may adjust the bias voltage of the photodetector to adjust the amplitude of the electrical signal generated by the photodetector in response to receiving the light beam. As another example, the controller may adjust the gain of the signal amplifier and/or the signal conditioning circuit to adjust the signal amplitude.

In some embodiments, detector gain control may be implemented in an open loop or closed loop method or a hybrid version of both. For example, in open loop control, the controller may look up the target gain of the detector for each vertical detection angle of beam emission and adjust the gain of the detector to the target gain. As another example, in closed loop control, a saturation detection circuit may be used to detect the saturation state of the detector. When saturation occurs, the controller may decrease the gain of the detector in response until the gain decreases to a level that eliminates the saturation condition in the detector. In some embodiments, the saturation detection circuit may distinguish which component(s) of the detector result in saturation, and the controller may specifically adjust the gain of that component(s) to address the saturation problem.

By dynamically and adaptively changing the receiver gain, the present embodiments thus improve the performance of the optical sensing system. For example, by avoiding saturation of the receiver end, the detection accuracy of the optical sensing system can be improved. On the other hand, reducing the received power in the receiver also contributes to the thermal efficiency of the system. The improved optical sensing system may be used in a number of applications. For example, the improved optical sensing system may be used in advanced navigation technologies, such as assisting in autopilot or generating high definition maps, where the optical sensing system may be mounted on a vehicle.

For example, fig. 1 is a schematic diagram of an exemplary vehicle 100 equipped with an optical sensing system (e.g., lidar system) 102 (also referred to below as lidar system 102) according to an embodiment of the present description. According to some embodiments, the vehicle 100 may be a survey vehicle configured for acquiring data to construct a high definition map or 3D building and city model. The vehicle 100 may also be an autonomous vehicle.

As shown in fig. 1, a vehicle 100 may be equipped with a lidar system 102 mounted to a body 104 of the vehicle via a mounting structure 108. The mounting structure 108 may be an electromechanical device that is mounted or otherwise attached to the body 104 of the vehicle 100. In some embodiments of the present disclosure, the mounting structure 108 may use screws, adhesive, or other mounting mechanisms. The vehicle 100 may be additionally equipped with sensors 110 inside or outside the body 104 using any suitable mounting mechanism. The sensors 110 may include sensors used in navigation units, such as a Global Positioning System (GPS) receiver and one or more Inertial Measurement Unit (IMU) sensors. It is contemplated that the manner in which lidar system 102 or sensor 110 is mounted on vehicle 100 is not limited by the example shown in fig. 1, and may be modified depending on the type of lidar system 102 and sensor 110 and/or vehicle 100 to achieve the desired 3D sensing performance.

According to some embodiments, lidar system 102 and sensor 110 may be configured to capture data as vehicle 100 moves along a trajectory. For example, the transmitter of lidar system 102 may be configured to scan the surrounding environment. The lidar system 102 measures the distance to the target by illuminating the target with a pulsed laser beam and measuring the reflected/scattered pulses with a receiver. The laser beam for the lidar system 102 may be ultraviolet, visible or near infrared. In some embodiments of the present description, lidar system 102 may capture a point cloud that includes depth information of objects in the surrounding environment. The lidar system 102 may continuously capture data as the vehicle 100 moves along a trajectory. Each set of scene data captured at a particular time range is referred to as a data frame.

In some embodiments, lidar system 102 may be mounted at a particular elevation above the ground (e.g., h0 as shown in fig. 1) such that it may scan objects within a range of elevations using laser beams emitted at different vertical detection angles. For example, FIG. 1 shows a field of view (FOV) consisting of a series of perpendicular detection angles to cover an object 112 at a height h1 above the ground. The vertical detection angle of the laser beam upward with respect to the horizontal direction (for example, the angle α as shown in fig. 1) may be referred to as a elevation angle, and the vertical detection angle of the laser beam downward with respect to the horizontal direction (for example, the angle θ as shown in fig. 1) may be referred to as a depression angle.

In some embodiments, the vertical detection angle of the lidar system may be adjusted by mounting structures 108 and/or scanners within the lidar system 102. In some embodiments, the vertical detection angle may also be affected by the attitude of the vehicle 100, for example, whether the vehicle 100 is traveling uphill or downhill. When the top view angle θ is larger than a certain value, the laser beam emitted from the lidar system 102 may be irradiated onto the ground, and the corresponding detection distance may be smaller than the maximum detection distance. In this case, since the distance traveled by the laser beam is short, attenuation is small, and the remaining power in the returned laser beam is high. In this description, lidar system 102 is configured to dynamically and adaptively adjust receiver gain as the laser beam is received during scanning to compensate for shorter detection distances at larger vertical detection angles θ.

Fig. 2 is a block diagram of an exemplary lidar system 102 shown in accordance with an embodiment of the present description. Lidar system 102 may include a transmitter 202, a receiver 204, and a controller 206. The emitter 202 may emit a light beam (e.g., a laser beam) in multiple directions. The transmitter 202 may include one or more laser sources 208 and a scanner 210. As shown in fig. 2, the emitter 202 may sequentially emit pulsed laser beam streams in different directions within a scan FOV (e.g., angular range).

The laser source 208 may be configured to provide a laser beam 207 (also referred to as a "primary laser beam") to a scanner 210. In some embodiments of the present description, the laser source 208 may generate a pulsed laser beam in the ultraviolet, visible, or near infrared wavelength range. In some embodiments of the present description, the laser source 208 may include a Pulsed Laser Diode (PLD), a Vertical Cavity Surface Emitting Laser (VCSEL), a fiber laser, or the like. For example, a PLD may be a semiconductor device similar to a Light Emitting Diode (LED), in which a laser beam is generated at the junction of the diode. In some embodiments of the present description, the PLD includes a PIN diode in which the active region is located in the intrinsic (I) region, and carriers (electrons and holes) are pumped into the active region from the N-region and the P-region, respectively. Depending on the semiconductor material, the wavelength of the incident laser beam 207 provided by PLD may be less than 1100nm, e.g., 405nm, 445nm and 465nm, 510nm and 525nm, 532nm, 635nm, 650nm and 660nm, 670nm, 760nm, 785nm, 808nm, 848nm, or 905nm. It is understood that any suitable laser source may be used as the laser source 208 that emits the laser beam 207.

The scanner 210 may be configured to emit a laser beam 209 (as shown in fig. 1, together forming the FOV of the emitter 202) toward an object 212 over a range of vertical detection angles. The vertical detection angle may be a upward angle (pointing upward from horizontal) or a downward angle (pointing downward from horizontal). In some embodiments, scanner 210 may also include optical components (e.g., lenses, mirrors) that may collimate the pulsed laser light into a narrow laser beam to increase the scanning resolution and range of scanned object 212.

In some embodiments, object 212 may be made of a variety of materials including, for example, non-metallic objects, rocks, rain, compounds, aerosols, clouds, or even a single molecule. In some embodiments, at each point in time during the scan, the scanner 210 may emit the laser beam 209 toward the object 212 in a direction within the scan angle range by rotating a deflector (e.g., a micromachined mirror component).

In some embodiments, the receiver 204 may be configured to detect the return laser beam 211 returned from the object 212. The returned laser beam 211 may be in a different direction than the laser beam 209. The receiver 204 may collect the returned laser beam from the object 212 and output an electrical signal reflecting the intensity of the returned laser beam. Upon contact, the laser light may be reflected/scattered by the object 212 by backscattering (e.g., rayleigh scattering, mie scattering, raman scattering, and fluorescence). As shown in fig. 2, receiver 204 may include a lens 214 and a detector 216. The lens 214 may be configured to collect light from a corresponding direction in the receiver field of view (FOV) and to converge the light beam to focus on the detector 216. At each point in time during the scan, the returned laser beam 211 may be collected by lens 214. The returned laser beam 211 may be returned by the object 212 and have the same wavelength as the laser beam 209.

The detector 216 may be configured to detect the return laser beam 211 returned from the object 212 and converged by the lens 214. In some embodiments, the detector 216 may convert the laser light (e.g., the returned laser beam 211) converged by the lens 214 into an electrical signal 218 (e.g., a current or voltage signal). The detector 216 may have a gain defined as the ratio between the power of the electrical signal 218 and the power of the light beam received by the detector 216. The higher the gain, the higher the amplitude of the electrical signal 218. According to the present description, the gain of the detector 216 may be dynamically varied at different vertical detection angles of the light beam.

In some embodiments, the detector 216 may include several stages, and the gain of the detector 216 may be adjusted in one or more stages. For example, fig. 3 is a schematic diagram of an exemplary detector 300 in a receiver of a lidar system according to an embodiment of the present description. As shown in fig. 3, the detector 300 may include three stages: a photodetector 302, a signal amplifier 304, and a signal conditioning circuit 306. Each stage has its own gain, which is defined as the ratio between the output power and the input power, and the total gain of the detector 300 is the product of the gains of the various stages.

The photodetector 302 may include a photodiode that converts light into a current (also referred to as a photocurrent). In some embodiments, the photodetectors 302 may include PIN detectors, avalanche Photodiode (APD) detectors, single Photon Avalanche Diode (SPAD) detectors, silicon photomultiplier (SiPM) detectors, and the like. The photodiode generates a photocurrent when absorbing light. The ratio of the photocurrent generated by the incident light to the incident light power (referred to as the responsivity of the photodiode) can be controlled by adjusting the bias voltage of the photodiode. Thus, the gain of the detector 300 may be adjusted by varying the bias voltage of the photodetector 302.

The signal amplifier 304 may amplify the electrical signal generated by the photodetector 302. In some embodiments, the signal amplifier may be a transimpedance amplifier. The signal conditioning circuit 306 may further condition the electrical signal. In some embodiments, the signal conditioning circuit 306 may be a limiting amplifier, a logarithmic amplifier, a comparator, an analog-to-digital converter (ADC), or a time-to-digital converter (TDC). The gain of detector 300 may alternatively or additionally be adjusted by changing the gain of signal amplifier 304 and/or signal conditioning circuit 306.

In some embodiments, saturation may occur at one or more stages of the detector 300. For example, one or more of the photodetector 302, the signal amplifier 304, and the signal conditioning circuit 306 may be saturated. In some embodiments, saturation detection circuit 310 may be coupled with each of photodetector 302, signal amplifier 304, and signal conditioning circuit 306 to detect a saturation condition. In some embodiments, the gain of the saturation component may be reduced to eliminate saturation conditions.

Returning to fig. 2, the electrical signal 218 may be transmitted to a data processing unit, such as a signal processor 220 of the lidar system 102, for processing and analysis. For example, the signal processor 220 may determine the distance of the object 212 from the lidar system 102 based on the data of the electrical signal 218 and the laser beam 209. In some embodiments, the signal processor may be a Field Programmable Gate Array (FPGA), a microcontroller unit (MCU), a Central Processing Unit (CPU), a Digital Signal Processor (DSP), or the like. In some embodiments, the signal processor 220 may be part of the controller 206.

The controller 206 may be configured to control the transmitter 202 and/or the receiver 204 to perform detection/sensing operations. In some embodiments of the present description, the controller 206 may dynamically determine an appropriate gain for the detector 216 based on the vertical detection angle of the lidar system 102 and adjust the gain to an appropriate level. For example, the controller 206 may use a predetermined look-up table (LUT) to determine the target gain of the detector 216 corresponding to each vertical detection angle. In some embodiments, the target gain may be proportional to the square of the detection distance calculated for each vertical detection angle. In some further embodiments, the target gain is also proportional to the ratio of the reflectivity of the object 212 to the reflectivity of the ground. For example, the controller 206 may determine the reflectivity of the object 212 based on the returned laser beam received by the receiver 204. In another example, controller 206 may determine the threshold angle based on an elevation angle of lidar system 102 and a threshold detection distance of lidar system 102 above ground. The controller 206 may decrease the gain when the vertical detection angle exceeds a threshold angle. In yet another example, the controller 206 may decrease the gain when the saturation detection circuit 310 detects a saturation condition from the detector 216.

In some embodiments, the controller 206 may generate and send command signals to the detector 216 to adjust its gain. For example, the controller 206 may send a command signal to the photodetector 302 to adjust its bias voltage, thereby adjusting the photocurrent it produces. As another example, the controller 206 may send command signals to the signal amplifier 304 and/or the signal conditioning circuit 306 to adjust the respective gains.

For example, fig. 4 is a schematic diagram of an exemplary controller 206 for adjusting laser power of a lidar system according to an embodiment of the present description. As shown in fig. 4, the controller 206 may include a communication interface 402, a processor 404, a memory 406, and a storage 408. In some embodiments, the controller 206 may have different modules in a single device, such as an Integrated Circuit (IC) chip (e.g., implemented as an Application Specific Integrated Circuit (ASIC) or Field Programmable Gate Array (FPGA)), or a stand-alone device with dedicated functions. In some embodiments, one or more components of the controller 206 may be located in the cloud, or alternatively may be located in a single location (e.g., within the mobile device) or distributed locations. The components of the controller 206 may be in an integrated device or distributed in different locations but communicate with each other over a network (not shown). According to the present description, the controller 206 may be configured to dynamically control the gain of the detector 216 based on different vertical detection angles of the emitted laser beam. In some embodiments, controller 206 may also perform various other control functions for other components of lidar system 102.

The communication interface 402 may transmit signals to and receive signals from components of the transmitter 202 and receiver 204 (e.g., the detector 216 and its components) through wired communication means, such as serializer/deserializers (SerDes), low Voltage Differential Signals (LVDS), serial Peripheral Interfaces (SPI), etc. In some embodiments, communication interface 402 may optionally use a wireless communication means, such as a Wireless Local Area Network (WLAN), a Wide Area Network (WAN), a wireless network (e.g., radio waves), a cellular network, and/or a local or short range wireless network (e.g., bluetooth) ^TM ) Etc. Communication interface 402 may send and receive electrical, electromagnetic or optical signals in analog or digital form.

According to some embodiments, the communication interface 402 may receive scan parameters, such as a vertical detection angle of an emitted laser beam, from the emitter 202. The communication interface 402 may also receive detection results from the saturation detection circuit 310. The communication interface 402 may provide command signals to the detector 216 to dynamically adjust its gain. Communication interface 402 may also receive acquired signals from and provide control signals to various other components of lidar system 102.

Processor 404 may include any suitable type of general purpose or special purpose microprocessor, digital signal processor, or microcontroller. Processor 404 may be configured as a separate processor module dedicated to lidar transmit power control, for example, to dynamically determine a target gain for detector 216 for receiving beams of light at different vertical detection angles, and to generate command signals to adjust the gain of detector 216 to the target gain. Alternatively, the processor 404 may be configured as a shared processor module for performing other functions of lidar control.

Memory 406 and storage 408 may comprise any suitable type of mass storage provided to store any type of information that processor 404 may need to operate. Memory 406 and storage 408 may be volatile or nonvolatile, magnetic, semiconductor, tape, optical, removable, non-removable, or other types of storage devices or tangible (i.e., non-transitory) computer readable media, including, but not limited to, ROM, flash memory, dynamic RAM, and static RAM. Memory 406 and/or storage 408 may be configured to store one or more computer programs that may be executed by processor 404 to perform the functions disclosed herein. For example, memory 406 and/or storage 408 may be configured to store one or more programs for dynamic receiver gain control in a lidar that may be executed by processor 404. In some embodiments, memory 406 and/or storage 408 may further store a predetermined look-up table that maps each vertical detection angle to a corresponding pre-calculated target gain. In some embodiments, memory 406 and/or storage 408 may also store intermediate data, such as threshold vertical detection angles, detection distances corresponding to different vertical detection angles, reflectivity of the scanned object, desired gains for the respective vertical detection angles, and the like.

As shown in fig. 4, the processor 404 may include a plurality of modules, for example, a detection distance determination unit 442, a gain determination unit 444, a saturation detection unit 446, and a command signal generation unit 448, and the like. These modules may be hardware elements (e.g., portions of an integrated circuit) of the processor 404 that are designed for use with other components or software elements of the processor 404 implemented by executing at least a portion of a program. The program may be stored on a computer readable medium and when executed by the processor 404 may perform one or more functions. Although FIG. 4 shows units 442-448 as being entirely within one processor 404, it is contemplated that the units may be distributed among different processors located closer or farther from each other.

In some embodiments, the detection distance determination unit 442 may calculate detection distances corresponding to respective vertical detection angles within the emitter FOV. For example, fig. 5 is a view of a vertical probe angle and corresponding probe distance used during lidar scanning according to an embodiment of the present disclosure. As shown in fig. 5, lidar system 102 may be located at a height h0 above ground level. For example, lidar system 102 may be mounted on vehicle 100 and thus elevated above the ground. Lidar system 102 may have a maximum detection distance d _max (also referred to as a threshold detection distance) that corresponds to a horizontal distance between object 112 and lidar system 102.

In some embodiments, the detection distance may be calculated as a function of the vertical detection angle (e.g., the top view angle θ as shown in fig. 5). For example, if a vehicle mounted with lidar system 102 is traveling on a slope (e.g., uphill or downhill), the vertical detection angle may be determined based on the vertical scan angle of scanner 210, the tilt angle of lidar system 102 (e.g., via mounting structure 108), and the elevation angle. In some embodiments, the vertical scan angle of scanner 210 may be stored in controller 206 or obtained from another controller that controls the scanning of the laser beam. If the tilt angle and/or elevation angle is non-zero, the tilt angle and/or elevation angle is subtracted from the vertical scan angle to obtain the vertical detection angle. For example, if the vertical scan angle is 40 °, lidar system 102 is mounted to tilt up by 10 °, and vehicle 100 is traveling downhill on a 15 ° incline (i.e., -15 ° elevation angle), then the vertical detection angle is determined to be 40 ° -10 ° - (-15 °) =45°.

In some embodiments, the detection distance may be calculated differently for perpendicular detection angles in two ranges: a first range [0, θa ], where θa is a threshold angle, and a second range [ θa,90 °). In some embodiments, the threshold angle θa may be determined according to equation (1):

Where h0 is the elevation of lidar system 102 above ground, d _max Is the maximum detection distance.

When the vertical detection angle (e.g., the top view angle θ as shown in fig. 5) is smaller than θa (i.e., within the first range), the detection distance remains d _max . When the top view angle θ is larger than θa (i.e., within the second range), the detection distance d _θ And becomes smaller. In some embodiments, the probe distance may be determined using equation (2):

based on the determined detection distance, the gain determination unit 444 may calculate a target gain of the detector 216. In some embodiments, for a specific maximum detection distance d _max Short detection distance d _θ (i.e., for a vertical detection angle θ greater than a threshold angle θa), the gain determination unit 444 may change the detector gain from a maximum gain G _max To a smaller but sufficient level. In some embodiments, the target gain may be proportional to the square of the respective detection distance. In some further embodiments, the target gain is proportional to a ratio of the first reflectivity of the target object to the second reflectivity of the ground. For example, the gain determination unit 444 may calculate the target gain (G) of the depression angle θ according to equation (3) _θ )：

Wherein G is _max Is the maximum gain of detector 216, ρ _object Is the reflectivity of the target object ρ _ground Is the reflectivity of the ground, d _θ Is the detection distance of the overlooking angle theta, d _max Is the maximum detection distance. In some embodiments, the reflectivity of the ground may be predetermined and preprogrammed into the controller 206. In some embodiments, the reflectivity of the target object (e.g., object 112) may be dynamically determined based on the return laser beam signal received by receiver 204 in real-time.

In some embodiments, a target gain G corresponding to each vertical detection angle θs of the beam _θs The calculation may be performed off-line according to equations (1) - (3), e.g., by a separate processor. The mapping between target gain and vertical detection angle may be recorded in a look-up table and preprogrammed in the controller 206. For example, the lookup table may be stored in memory 406 or storage 408 of controller 206. According to such an embodiment, the calculation performed by the probe distance determination unit 442 described above may be skipped. The gain determination unit 444 may determine the target gain by looking up the vertical probe angle θ in a lookup table.

In some embodiments, the saturation detection unit 446 may determine whether a saturation condition has occurred based on the detection result provided by the saturation detection circuit 310. In some embodiments, if a saturation condition is detected, the saturation detection unit 446 may additionally determine where the saturation condition occurs, for example, in the photodetector 302, the signal amplifier 304, and/or the signal conditioning circuit 306.

The command signal generation unit 448 may generate a command signal to adjust the gain of the detector 216 according to the determination of the gain determination unit 444 and/or the saturation detection unit 446. In some embodiments, when open loop control is used, a command signal may be generated based on the target gain determined by the gain determination unit 444 in order to adjust the gain of the detector 216 to the target gain. The open loop control method will be described in more detail in connection with fig. 6. In some alternative embodiments, when closed loop control is used, a command signal may be generated when a saturation condition is detected to reduce the gain of the detector 216 until the gain is reduced to a level where the saturation condition no longer exists. The closed loop control method will be described in more detail in connection with fig. 7. In still other alternative embodiments, a hybrid control approach may be used. For example, the gain determination unit 444 may first generate an initial command signal to adjust the gain of the detector 216 to the target gain determined by the gain determination unit 444, and then generate another command signal to fine tune the gain until the saturation condition is removed from the detector 216.

In some embodiments, the command signal may adjust the gain of one or more stages in the detector 216. For example, the command signal may adjust the bias voltage of the photodetector 302, and/or the gain of the signal amplifier 304 and/or the signal conditioning circuit 306. In some embodiments, command signals may be provided to the respective components to adjust their gains to eliminate saturation conditions based on the locations at which saturation conditions determined by the saturation detection unit 446 occur.

Fig. 6 is a flow chart of an exemplary open loop control method 600 for adjusting the receiver gain of a lidar system according to an embodiment of the present disclosure. In some embodiments, method 600 may be performed by various components of lidar system 102, such as receiver 204 and controller 206. In some embodiments, method 600 may include step S602-step S618. It should be understood that some steps may be optional. In addition, some steps may be performed simultaneously or in a different order than shown in fig. 6.

In step S602, the controller 206 may determine a vertical detection angle of the current scan angle. In some embodiments, the controller 206 may receive the current scan angle used by the transmitter 202. In some embodiments, the controller 206 may be the same controller that determines the scan parameters and thus saves the parameters in its memory/storage. Thus, the controller 206 may retrieve the scan angle from its own memory/storage. Otherwise, the controller 206 may receive the scan angle from an external source. In some embodiments, detection distance determination unit 442 may first determine the current vertical detection angle based on the scan angle adjusted by the tilt angle of lidar system 102 and the elevation angle of the vehicle as it travels on the incline.

In step S604, the controller 206 may calculate a detection distance corresponding to the current vertical detection angle. For example, when the vertical detection angle θ is smaller than the threshold angle θa calculated according to equation (1), the detection distance determination unit 342 may determine that the detection distance remains the maximum detection distance d _max . When the angle θ exceeds θa, the detection distance determination unit 342 may determine the detection distance using a trigonometric function of the height h0 and the angle θ (e.g., according to equation (2)).

In step S606, the controller 206 may determine a detector gain for receiving the light beam emitted at the current scan angle based on the detection distance determined in step S604. In some embodiments, for a specific maximum detection distance d _max Short detection distance d _θ The gain determination unit 444 may change the gain from the maximum gain G _max To a smaller but sufficient level. In some embodiments, the target gain may be proportional to the square of the respective detection distance. In some further embodiments, the transmit power level is proportional to a ratio of the first reflectivity of the target object to the second reflectivity of the ground. For example, the gain determination unit 344 may calculate the target gain according to equation (3).

In step S608, the controller 206 may generate a command signal corresponding to the target gain determined in step S606. In some embodiments, command signals may be generated to adjust the bias voltage of the photodetector 302 and/or the gain of the signal amplifier 304 and/or the signal conditioning circuit 306. In step S610, the controller 206 may provide command signals to the corresponding components of the detector 216 to adjust the gain to the target gain.

In step S612, the receiver 204 may detect the beam returned by the target object using the detector 216. For example, the receiver 204 may detect the return laser beam 211 returned from the object 212. The receiver 204 may collect the laser beam returned from the object 212 and output an electrical signal reflecting the intensity of the returned laser beam according to the gain adjustment. In step S614, the controller 206 may determine the reflectivity of the target object based on the intensity of the returned laser beam. In step S606, the target gain may be determined using the reflectivity of the object. For example, the target gain may be further adjusted by a ratio of the reflectivity of the target object and the reflectivity of the ground.

In step S616, the controller 206 may determine whether all scan angles of the scanner 210 have been covered and, if not (S616: NO), the method 600 proceeds to step S618, e.g., by repeating steps S602-S616, to determine and adjust the detector gain for the next scan angle. The method 600 ends after the scanner 210 passes through all scan angles (S616: yes).

In some embodiments, steps S604-S606 may be performed offline for all vertical detection angles to determine the corresponding target gains. The results may be recorded in a lookup table and stored with the controller 206. In real-time execution, the method 600 may skip S604 and S606, and instead, the method 600 may include the step of the controller 206 looking up a target gain corresponding to the current vertical detection angle from a predetermined look-up table. By using a look-up table, the computational cost can be significantly reduced.

Fig. 7 is a flow chart of an exemplary closed loop control method 700 for adjusting the receiver gain of a lidar system according to an embodiment of the present description. In some embodiments, method 700 may be performed by various components of lidar system 102, such as receiver 204 and controller 206. In some embodiments, method 700 may include step S702-step S714. It should be understood that some steps may be optional. In addition, some steps may be performed simultaneously or in a different order than shown in fig. 7.

In step S702, the controller 206 may detect the saturation state of the detector 216 based on the detection result provided by the saturation detection circuit 310. In some embodiments, if a saturation condition is detected, the controller 206 may additionally determine where the saturation condition occurs, for example, in the photodetector 302, the signal amplifier 304, and/or the signal conditioning circuit 306.

In step S704, the controller 206 may generate a command signal to decrease the gain of the detector 216. In some embodiments, to reduce the overall gain of the detector 216, a command signal may be generated to adjust the bias voltage of the photodetector 302 and/or the gain of the signal amplifier 304 and/or the signal conditioning circuit 306. In step S706, the controller 206 may provide command signals to various components of the detector 216 to adjust the gain to a target gain.

In step S708, the receiver 204 may detect the beam returned by the target object using the detector 216. In step S710, the controller 206 may determine whether the saturation condition has disappeared. Reducing the gain of the detector 216 helps reduce the electrical signal produced by the detector 216, thereby leaving the detector 216 outside of the saturation region. If the saturation condition does not disappear (S710: NO), the method 700 returns to steps S704-S706 to continue generating and providing command signals to further reduce the gain. If the saturation condition has disappeared (S710: yes), the method 700 may proceed to step S712, in which the controller 206 determines whether all scan angles of the scanner 210 have been covered. If not (S712: NO), the method 700 proceeds to step S714, where the detector gain for the next scan angle is adjusted, for example, by repeating steps S702-S712. The method 700 ends after the scanner 210 passes through all scan angles (S712: yes).

In some embodiments, the hybrid control method may be implemented by combining certain steps of method 600 and method 700. For example, for each scan angle, the controller 206 may first perform open loop control of steps S602-S614 to adjust the gain to the determined target gain. The controller 206 may then perform closed loop control of steps S702-S710 to fine tune the gain to ensure that no saturation conditions exist.

In some embodiments, the systems and methods described in the present disclosure may be combined with those described in U.S. application Ser. No. 16/920650, which is incorporated herein by reference. For example, the transmitter power level and receiver gain may be adjusted to collectively compensate for variations in detection range of the lidar system at different vertical detection angles.

Although this description is made using a lidar system as an example, the disclosed embodiments may be applicable to and implemented as other types of optical sensing systems that use a receiver to receive optical signals that are not limited to laser beams. For example, embodiments may be readily adapted to optical imaging systems or radar detection systems that scan objects using electromagnetic waves.

Another aspect of the specification relates to a non-transitory computer-readable medium storing instructions that, when executed, cause one or more processors to perform a method as described above. The computer-readable medium may include volatile or nonvolatile, magnetic, semiconductor-based, tape-based, optical, removable, non-removable, or other types of computer-readable media or computer-readable storage devices. For example, as disclosed, the computer-readable medium may be a storage device or memory module having computer instructions stored thereon. In some embodiments, the computer readable medium may be a disk or flash drive having computer instructions stored thereon.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed systems and related methods. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed systems and related methods.

It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.

Claims

1. An optical sensing system, comprising:

An emitter configured to emit light beams at a plurality of perpendicular detection angles to scan an object;

a receiver comprising a detector configured to detect a beam of light returned by the object; and

a controller configured to dynamically vary the gain of the detector for detecting the light beam at each vertical detection angle.

2. The optical sensing system of claim 1, wherein to dynamically change the gain of the detector, the controller is further configured to: the gain is reduced when the vertical detection angle exceeds a threshold angle, wherein the threshold angle is determined based on an elevation angle of the optical sensing system above ground and a threshold detection distance of the optical sensing system.

3. The optical sensing system of claim 1, wherein the controller is configured to vary the detector gain based on a predetermined look-up table for mapping the respective vertical detection angles to a target detector gain.

4. The optical sensing system of claim 3, wherein the target detector gain is proportional to a square of a respective detection distance determined based on an elevation angle of the optical sensing system above ground and the respective vertical detection angle.

5. The optical sensing system of claim 3, wherein the controller is further configured to:

determining a first reflectivity of the object based on the light beam received by the receiver; and is also provided with

The gain of the detector is adjusted by the ratio of the first reflectivity to the second reflectivity of the ground.

6. The optical sensing system of claim 3, further comprising a saturation detection circuit configured to detect a saturation condition of the detector, wherein the controller is further configured to fine tune a gain of the detector until the saturation condition disappears.

7. The optical sensing system of claim 1, further comprising a saturation detection circuit coupled to the detector, wherein the controller is configured to reduce a gain of the detector when the saturation detection circuit detects a saturation state of the detector when the light beam at a vertical detection angle is received.

8. The optical sensing system of claim 7, wherein the detector comprises a photodetector, a signal amplifier, and a signal conditioning circuit, wherein the controller is configured to reduce a gain of the photodetector, the signal amplifier, or the signal conditioning circuit when the saturation detection circuit detects the saturation condition from the photodetector, the signal amplifier, or the signal conditioning circuit.

9. The optical sensing system of claim 1, wherein the detector comprises a photodetector configured to generate an electrical signal in response to receiving the light beam at the respective vertical detection angle, wherein to dynamically change a gain of the detector, the controller is further configured to change a bias voltage of the photodetector.

10. The optical sensing system of claim 1, wherein the detector comprises a signal amplifier configured to amplify an electrical signal generated in response to receiving the light beam for the respective vertical detection angle, wherein to dynamically change the gain of the detector, the controller is further configured to change the gain of the signal amplifier.

11. The optical sensing system of claim 1, wherein the detector comprises a signal conditioning circuit configured to condition an electrical signal generated in response to receiving the light beams at the respective vertical detection angles, wherein to dynamically change a gain of the detector, the controller is further configured to change a gain of the signal conditioning circuit.

12. The optical sensing system of claim 1, wherein the optical sensing system is a light detection and ranging (lidar) system.

13. A method for controlling receiver gain in an optical sensing system, comprising:

transmitting a light beam at a plurality of vertical detection angles by an emitter to scan an object;

detecting the beam returned by the object by a detector in the receiver; and

the gain of the detector for detecting the light beam at each vertical detection angle is dynamically changed by a controller.

14. The method of claim 13, further comprising reducing a gain of the detector when the vertical detection angle exceeds a threshold angle, wherein the threshold angle is determined based on an elevation angle of the optical sensing system above ground and a threshold detection distance of the optical sensing system.

15. The method of claim 13, wherein the detector gain is dynamically changed based on a predetermined look-up table for mapping the respective vertical detection angles to a target detector gain.

16. The method of claim 15, wherein the target detector gain is proportional to a square of a respective detection distance determined based on an elevation angle of the optical sensing system above ground and the respective vertical detection angle.

17. The method of claim 15, wherein dynamically changing the gain of the detector further comprises:

detecting a saturation condition of the detector by a saturation detection circuit; and

the gain of the detector is fine-tuned by the controller until the saturation condition disappears.

18. The method of claim 13, wherein dynamically changing the gain of the detector further comprises: and when the saturation detection circuit detects the saturation state of the detector when receiving the light beam with the vertical detection angle, reducing the gain of the detector.

19. The method of claim 13, wherein the detector comprises a photodetector configured to generate an electrical signal in response to receiving the light beams at the respective vertical detection angles, wherein dynamically changing the gain of the detector further comprises changing a bias voltage of the photodetector.

20. A receiver in an optical sensing system, comprising:

a detector configured to detect a beam returned by an object scanned by the emission beam at a plurality of perpendicular detection angles; and

a controller configured to dynamically change the gain of the detector based on a predetermined look-up table mapping each vertical detection angle to a target detector gain, wherein the target detector gain is proportional to the square of a detection distance determined based on the elevation angle of the optical sensing system above ground and the respective vertical detection angle.