Dynamic receiver gain control for lidar systems

Abstract

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

Description

[0001] Cross-referencing

[0002] This application claims priority to U.S. Patent Application No. 16 / 995,423, filed August 17, 2020, entitled "Dynamic Receiver Gain Control for a LiDAR System," which is a partial continuation of U.S. Patent Application No. 16 / 920,650, filed July 3, 2020, entitled "Dynamic Laser Power Control for a LiDAR System," the contents of which are incorporated herein by reference. Technical Field

[0003] This specification relates to gain control for optical detection and ranging (LiDAR) systems, and more specifically, to dynamically controlling receiver gain to compensate for variations in detection distance at different vertical detection angles of the LiDAR system. Background Technology

[0004] Optical sensing systems such as lidar have been widely used in advanced navigation technologies, such as assisted autonomous driving or high-definition map generation. For example, a typical lidar system measures the distance to a target by illuminating it with a pulsed laser beam and measuring the reflected pulses with sensors (e.g., detectors or detector arrays). Differences in the laser return time, wavelength, and / or phase can then be used to construct a digital three-dimensional (3D) representation of the target. Because using a narrow laser beam as the incident light allows for the mapping of physical features at very high resolution, lidar systems are particularly well-suited for applications such as autonomous driving sensing and high-definition mapping.

[0005] A pulsed laser beam emitted by a lidar system is typically pointed in multiple directions to cover the field of view (FOV). For example, the vertical detection angle of a lidar system (called the top angle when the scanning laser beam is pointed downwards) varies to scan objects in vertical space. The required detection distance varies with the vertical detection angle. For example, when the top angle is small, i.e., the lidar emits the scanning laser beam almost horizontally, the distance towards the object is long. On the other hand, as the top angle increases, the distance towards the ground becomes shorter.

[0006] Laser beams reflected from objects at shorter distances (e.g., close to the ground) can carry higher power. However, conventional lidar systems use a constant receiver gain for different vertical detection angles. Therefore, laser beams reflected from shorter distances can cause receiver saturation. Receiver saturation reduces the accuracy of its distance and intensity measurements and leads to other problems such as receiver overheating and instability.

[0007] The embodiments in this specification improve the performance of optical sensing systems, such as lidar systems, by implementing dynamic receiver gain control to compensate for changes in detection distance at different vertical detection angles of the sensing system. Summary of the Invention

[0008] This specification provides an embodiment of an optical sensing system. An exemplary optical sensing system includes a transmitter configured to emit light beams at multiple vertical detection angles to scan an object. The optical sensing system also includes a receiver having detectors configured to detect light beams reflected back from the object. The optical sensing system further includes a controller configured to dynamically change the gain of the detectors used to detect the light beams at the respective vertical detection angles.

[0009] This specification also provides a method for controlling the gain of a receiver in an optical sensing system. The method includes emitting a light beam at multiple vertical detection angles via a transmitter to scan an object. The method further includes detecting the light beam reflected back by the object via a detector in the receiver. The method also includes dynamically changing the gain of the detector used to detect the light beam at each vertical detection angle via a controller.

[0010] This specification further provides a receiver in an optical sensing system. The receiver includes a detector configured to detect light beams returned by an object emitting light beams at multiple vertical detection angles. The receiver also includes a controller configured to dynamically change the gain of the detector based on a predetermined lookup table mapping the respective vertical detection angles to the gain of a target detector. The target detector gain is proportional to the square of the detection distance, which is determined based on the elevation angle of the optical sensing system located above the ground and the corresponding vertical detection angles.

[0011] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only, and not intended to limit the claimed invention. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of an exemplary vehicle equipped with a lidar system according to an embodiment of this specification.

[0013] Figure 2 This is a block diagram of an exemplary lidar system according to embodiments of this specification.

[0014] Figure 3 This is a schematic diagram of an exemplary detector in the receiver of a lidar system according to an embodiment of this specification.

[0015] Figure 4 This is a schematic diagram of an exemplary controller for adjusting the receiver gain of a lidar system, as shown in an embodiment of this specification.

[0016] Figure 5The vertical detection angle and corresponding detection distance used during lidar scanning are as shown in the embodiments of this specification.

[0017] Figure 6 This is a flowchart of an exemplary open-loop control method for adjusting the receiver gain of a lidar system, as shown in an embodiment of this specification.

[0018] Figure 7 This is a flowchart of an exemplary closed-loop control method for adjusting the receiver gain of a lidar system, as shown in an embodiment of this specification. Detailed Implementation

[0019] Reference will now be made in detail to exemplary embodiments, examples of which are shown in the accompanying drawings. Where possible, the same reference numerals will be used throughout the drawings to refer to the same or similar parts.

[0020] This specification provides embodiments of 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 a transmitter configured to emit a light beam (e.g., a laser beam) at multiple vertical detection angles to scan an object. Smaller vertical detection angles result in longer detection distances, while larger vertical detection angles result in shorter detection distances. The emitted light beam is reflected from the scanned object and returns, and is received by a receiver in the optical sensing system. For example, the receiver may include a detector that detects the returned light beam.

[0021] In some embodiments, the optical sensing system includes a controller configured to dynamically change the gain of a detector for receiving light beams emitted at various vertical detection angles. For example, the detector gain can be adjusted based on the detection distance at each vertical detection angle, since the light beam returning from a shorter detection distance carries higher laser power, thus ensuring the use of a lower gain. In some embodiments, the detector gain can vary proportionally to the square of the detection distance. In some further embodiments, the detector gain can be further adjusted by the ratio of the reflectivity of the object to the reflectivity of the ground. As another example, the controller can determine a threshold angle based on the elevation angle of the optical sensing system above the ground and a threshold detection distance of the optical sensing system. Then, when the vertical detection angle exceeds the threshold angle, the controller reduces the detector gain.

[0022] In some embodiments, the detector may further include a photodetector, a signal amplifier, and a signal conditioning circuit, and the gain of the detector can be changed 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 a 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.

[0023] In some embodiments, detector gain control can be implemented using open-loop or closed-loop methods, or a hybrid of both. For example, in open-loop control, the controller can find the target gain of the detector for each vertical detection angle of the beam emission and adjust the detector gain to the target gain. As another example, in closed-loop control, a saturation detection circuit can be used to detect the saturation state of the detector. When saturation occurs, the controller can reduce the detector gain in response until the gain is reduced to a level that eliminates the saturation condition in the detector. In some embodiments, the saturation detection circuit can distinguish which(s) of the detector is causing saturation, and the controller can specifically adjust the gain of that(s) to address the saturation problem.

[0024] By dynamically and adaptively adjusting the receiver gain, the embodiments of this specification thus improve the performance of the optical sensing system. For example, by avoiding saturation at the receiver end, the detection accuracy of the optical sensing system can be improved. On the other hand, reducing the receiving power in the receiver also benefits the thermal efficiency of the system. The improved optical sensing system can be used in many applications. For example, the improved optical sensing system can be used in advanced navigation technologies, such as assisted autonomous driving or generating high-definition maps, wherein the optical sensing system can be mounted on a vehicle.

[0025] For example, Figure 1 This is a schematic diagram of an exemplary vehicle 100 equipped with an optical sensing system (e.g., a lidar system) 102 (hereinafter also referred to as lidar system 102) according to embodiments of this specification. According to some embodiments, vehicle 100 may be a survey vehicle configured to acquire data to construct high-definition maps or 3D building and city models. Vehicle 100 may also be an autonomous vehicle.

[0026] like Figure 1As shown, vehicle 100 may be equipped with a lidar system 102 mounted to vehicle body 104 via mounting structure 108. Mounting structure 108 may be an electromechanical device that is mounted or otherwise attached to the vehicle body 104 of vehicle 100. In some embodiments of this specification, mounting structure 108 may use screws, adhesives, or other mounting mechanisms. Vehicle 100 may additionally equip sensor 110 inside or outside vehicle body 104 using any suitable mounting mechanism. Sensor 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... Figure 1 The example shown is a limitation and can be modified according to the type of LiDAR system 102 and sensor 110 and / or vehicle 100 to achieve the desired 3D sensing performance.

[0027] According to some embodiments, the lidar system 102 and sensor 110 can be configured to capture data as the vehicle 100 moves along a trajectory. For example, the transmitter of the lidar system 102 can 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 used for the lidar system 102 can be ultraviolet, visible, or near-infrared light. In some embodiments of this specification, the lidar system 102 can capture a point cloud including depth information of objects in the surrounding environment. As the vehicle 100 moves along the trajectory, the lidar system 102 can continuously capture data. Each set of scene data captured within a specific time range is referred to as a data frame.

[0028] In some embodiments, the lidar system 102 may be installed at a specific height above the ground (e.g., as shown in the image). Figure 1 As shown in h0), it allows it to scan objects within a certain height range using laser beams emitted at different vertical detection angles. For example, Figure 1 The field of view (FOV) is shown as a series of vertical detection angles to cover an object 112 at a height h1 above the ground. The laser beam is positioned relative to the vertical detection angles pointing upwards in the horizontal direction (e.g., as shown in the image). Figure 1 The angle α shown can be called the elevation angle, and the vertical detection angle of the laser beam relative to the horizontal direction downwards (e.g., Figure 1 The angle θ mentioned above can be called the downward angle.

[0029] In some embodiments, the vertical detection angle of the lidar system can be adjusted via the mounting structure 108 and / or a scanner 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 downward angle θ is greater than a certain value, the laser beam emitted by the lidar system 102 may illuminate the ground, and the corresponding detection distance may be less than the maximum detection distance. In this case, because the laser beam travels a shorter distance, the attenuation is smaller, and the residual power in the returned laser beam is higher. In this specification, the lidar system 102 is configured to dynamically and adaptively adjust the receiver gain when receiving the laser beam during scanning to compensate for the shorter detection distance at larger vertical detection angles θ.

[0030] Figure 2 This is a block diagram of an exemplary lidar system 102 according to embodiments of this specification. The lidar system 102 may include a transmitter 202, a receiver 204, and a controller 206. The transmitter 202 may emit light beams (e.g., laser beams) in multiple directions. The transmitter 202 may include one or more laser sources 208 and a scanner 210. Figure 2 As shown, transmitter 202 can sequentially emit pulsed laser beams in different directions within a scanning FOV (e.g., angular range).

[0031] Laser source 208 can be configured to provide laser beam 207 (also referred to as a “native laser beam”) to scanner 210. In some embodiments of this specification, laser source 208 can generate a pulsed laser beam in the ultraviolet, visible, or near-infrared wavelength range. In some embodiments of this specification, laser source 208 may include a pulsed laser diode (PLD), a vertical-cavity surface-emitting laser (VCSEL), a fiber laser, etc. For example, the PLD may be a semiconductor device similar to a light-emitting diode (LED), wherein the laser beam is generated at the junction of the diode. In some embodiments of this specification, the PLD includes a PIN diode, wherein the active region is located in the intrinsic (I) region, and charge carriers (electrons and holes) are pumped from the N-region and P-region, respectively, into the active region. Depending on the semiconductor material, the wavelength of the incident laser beam 207 provided by the PLD can be less than 1100 nm, for example, between 405 nm, 445 nm and 465 nm, 510 nm and 525 nm, 532 nm, 635 nm, between 650 nm and 660 nm, 670 nm, 760 nm, 785 nm, 808 nm, 848 nm, or 905 nm. It is understood that any suitable laser source can be used as the laser source 208 for emitting the laser beam 207.

[0032] Scanner 210 can be configured to emit a laser beam 209 (e.g., within a vertical detection angle range) toward object 212. Figure 1 As shown, these together form the field of view (FOV) of the transmitter 202. The vertical detection angle can be an upward angle (pointing up from the horizontal) or a downward angle (pointing down from the horizontal). In some embodiments, the scanner 210 may also include optical components (e.g., lenses, mirrors) that can collimate the pulsed laser into a narrow laser beam to increase the scanning resolution and the range of the scanned object 212.

[0033] In some embodiments, the object 212 may be made of a variety of materials, including, for example, non-metallic objects, rocks, rainwater, compounds, aerosols, clouds, or even single molecules. In some embodiments, at each point in time during scanning, the scanner 210 may emit a laser beam 209 toward the object 212 in a direction within the scanning angle range via a rotating deflector (e.g., a micromachining mirror component).

[0034] In some embodiments, receiver 204 can be configured to detect a returned laser beam 211 returning from object 212. The returned laser beam 211 may be in a different direction than laser beam 209. Receiver 204 can collect the returned laser beam from object 212 and output an electrical signal reflecting the intensity of the returned laser beam. Upon contact, the laser beam can be reflected / scattered by object 212 through backscattering (e.g., Rayleigh scattering, Mie scattering, Raman scattering, and fluorescence). Figure 2 As shown, receiver 204 may include lens 214 and detector 216. Lens 214 may be configured to collect light from a corresponding direction in the receiver's field of view (FOV) and converge the beam to focus it onto detector 216. At each time point during the scan, the returned laser beam 211 may be collected by lens 214. The returned laser beam 211 may be returned by object 212 and has the same wavelength as laser beam 209.

[0035] Detector 216 can be configured to detect a returning laser beam 211 that returns from object 212 and is focused by lens 214. In some embodiments, detector 216 can convert the laser focused by lens 214 (e.g., the returning laser beam 211) into an electrical signal 218 (e.g., a current or voltage signal). Detector 216 can have a gain defined as the ratio between the power of the electrical signal 218 and the power of the beam received by detector 216. The higher the gain, the higher the amplitude of the electrical signal 218. According to this specification, the gain of detector 216 can be dynamically varied at different vertical detection angles of the beam.

[0036] In some embodiments, detector 216 may include several stages, and the gain of detector 216 may be adjusted in one or more stages. For example, Figure 3This is a schematic diagram of an exemplary detector 300 in the receiver of a lidar system according to an embodiment of this specification. Figure 3 As shown, detector 300 may include three stages: photodetector 302, signal amplifier 304, and signal conditioning circuit 306. Each stage has its own gain, which is defined as the ratio between output power and input power, and the total gain of detector 300 is the product of the gains of each stage.

[0037] Photodetector 302 may include a photodiode that converts light into an electric current (also known as photocurrent). In some embodiments, photodetector 302 may include a PIN detector, an avalanche photodiode (APD) detector, a single-photon avalanche photodiode (SPAD) detector, and a silicon photomultiplier (SiPM) detector, etc. A photodiode generates a photocurrent when it absorbs light. The ratio of the photocurrent generated by the incident light to the incident light power (called the responsivity of the photodiode) can be controlled by adjusting the bias voltage of the photodiode. Therefore, the gain of detector 300 can be adjusted by changing the bias voltage of photodetector 302.

[0038] Signal amplifier 304 amplifies the electrical signal generated by photodetector 302. In some embodiments, the signal amplifier may be a transimpedance amplifier. Signal conditioning circuit 306 further conditions the electrical signal. In some embodiments, signal conditioning circuit 306 may be a limiting amplifier, logarithmic amplifier, comparator, analog-to-digital converter (ADC), or time-to-digital converter (TDC). The gain of detector 300 can be adjusted alternatively or additionally by changing the gain of signal amplifier 304 and / or signal conditioning circuit 306.

[0039] In some embodiments, saturation can occur at one or more stages of detector 300. For example, one or more of photodetector 302, signal amplifier 304, and signal conditioning circuit 306 can be saturated. In some embodiments, saturation detection circuit 310 can be coupled to each of photodetector 302, signal amplifier 304, and signal conditioning circuit 306 to detect saturation conditions. In some embodiments, the gain of the saturation components can be reduced to eliminate saturation conditions.

[0040] Back Figure 2The electrical signal 218 can be transmitted to a data processing unit, such as the signal processor 220 of the lidar system 102, for processing and analysis. For example, the signal processor 220 can determine the distance between the object 212 and the lidar system 102 based on the data from the electrical signal 218 and the laser beam 209. In some embodiments, the signal processor can be a field-programmable gate array (FPGA), a microcontroller unit (MCU), a central processing unit (CPU), a digital signal processor (DSP), etc. In some embodiments, the signal processor 220 can be part of a controller 206.

[0041] Controller 206 can be configured to control transmitter 202 and / or receiver 204 to perform detection / sensing operations. In some embodiments of this specification, controller 206 can dynamically determine and adjust the appropriate gain of detector 216 based on the vertical detection angle of lidar system 102. For example, controller 206 can use a predetermined lookup table (LUT) to determine the target gain of detector 216 corresponding to each vertical detection angle. In some embodiments, the target gain can 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 object 212 to the reflectivity of the ground. For example, controller 206 can determine the reflectivity of object 212 based on the returned laser beam received by receiver 204. In another example, controller 206 can determine a threshold angle based on the elevation angle of lidar system 102 located above the ground and the threshold detection distance of lidar system 102. When the vertical detection angle exceeds the threshold angle, controller 206 can reduce the gain. In yet another example, when the saturation detection circuit 310 detects a saturation condition from the detector 216, the controller 206 may reduce the gain.

[0042] In some embodiments, controller 206 may generate a command signal and send it to detector 216 to adjust its gain. For example, controller 206 may send a command signal to photodetector 302 to adjust its bias voltage, thereby adjusting the photocurrent it generates. As another example, controller 206 may send a command signal to signal amplifier 304 and / or signal conditioning circuit 306 to adjust their respective gains.

[0043] For example, Figure 4 This is a schematic diagram of an exemplary controller 206 for adjusting the laser power of a lidar system, as shown in an embodiment of this specification. Figure 4As shown, controller 206 may include communication interface 402, processor 404, memory 406, and storage 408. In some embodiments, controller 206 may have different modules in a single device, such as integrated circuit (IC) chips (e.g., implemented as application-specific integrated circuits (ASICs) or field-programmable gate arrays (FPGAs)), or stand-alone devices with dedicated functions. In some embodiments, one or more components of controller 206 may be located in the cloud, or alternatively, may be located in a single location (e.g., inside a mobile device) or distributed locations. Components of controller 206 may be in an integrated device or distributed in different locations but communicate with each other via a network (not shown). According to this specification, controller 206 may be configured to dynamically control the gain of 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 of other components of lidar system 102.

[0044] Communication interface 402 can transmit signals to and receive signals from components of transmitter 202 and receiver 204 (e.g., detector 216 and its components) via wired communication methods, such as serializer / deserializer (SerDes), low-voltage differential signaling (LVDS), serial peripheral interface (SPI), etc. In some embodiments, communication interface 402 can optionally use wireless communication methods, such as wireless local area network (WLAN), wide area network (WAN), wireless network (e.g., radio waves), cellular network, and / or local or short-range wireless network (e.g., Bluetooth). TM Communication interface 402 can send and receive analog or digital electrical signals, electromagnetic signals, or optical signals.

[0045] According to some embodiments, the communication interface 402 can receive scanning parameters from the transmitter 202, such as the vertical detection angle of the emitted laser beam. The communication interface 402 can also receive detection results from the saturation detection circuit 310. The communication interface 402 can provide command signals to the detector 216 to dynamically adjust its gain. The communication interface 402 can also receive acquired signals from various other components of the lidar system 102 and provide them with control signals.

[0046] 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, dynamically determining the target gain of detector 216 for receiving beams at different vertical detection angles and generating command signals to adjust the gain of detector 216 to that target gain. Alternatively, processor 404 may be configured as a shared processor module for performing other lidar control functions.

[0047] Memory 406 and memory 408 may include any suitable type of mass storage provided to store any type of information that processor 404 may need to operate. Memory 406 and memory 408 may be volatile or non-volatile, magnetic, semiconductor, magnetic 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 memory 408 may be configured to store one or more computer programs that can be executed by processor 404 to perform the functions disclosed herein. For example, memory 406 and / or memory 408 may be configured to store one or more programs for dynamic receiver gain control in a lidar system that can be executed by processor 404. In some embodiments, memory 406 and / or memory 408 may further store a predetermined lookup table that maps individual vertical detection angles to corresponding pre-calculated target gains. 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, and expected gain for each vertical detection angle.

[0048] like Figure 4 As shown, processor 404 may include multiple modules, such as a detection range determination unit 442, a gain determination unit 444, a saturation detection unit 446, and a command signal generation unit 448. These modules may be hardware units of processor 404 (e.g., portions of integrated circuits), designed for use with other components or software units implemented by processor 404 through the execution of at least a portion of a program. This program may be stored on a computer-readable medium and, when executed by processor 404, may perform one or more functions. Although Figure 4 Units 442-448 are shown all within a single processor 404, but it is conceivable that these units could be distributed across different processors located close to or far from each other.

[0049] In some embodiments, the detection distance determination unit 442 can calculate the detection distance corresponding to each vertical detection angle within the transmitter's field of view (FOV). For example... Figure 5 This refers to the vertical detection angle and corresponding detection distance used during lidar scanning, as shown in the embodiments of this specification. Figure 5 As shown, the lidar system 102 can be located at a height h0 above the ground plane. For example, the lidar system 102 can be mounted on the vehicle 100, thus raising it above the ground. The lidar system 102 can have a maximum detection range d. max(Also known as the threshold detection range), this maximum detection range corresponds to the horizontal distance between object 112 and lidar system 102.

[0050] In some embodiments, the detection distance can be calculated as the vertical detection angle (e.g., as shown in the figure). Figure 5 The vertical detection angle is a function of the top-view angle (θ). For example, if a vehicle equipped with the lidar system 102 is traveling on a slope (e.g., uphill or downhill), the vertical detection angle can be determined based on the vertical scan angle of the scanner 210, the tilt angle of the lidar system 102 (e.g., via the mounting structure 108), and the elevation angle. In some embodiments, the vertical scan angle of the scanner 210 can be stored in the controller 206 or obtained from another controller that controls the laser beam scanning. If the tilt angle and / or elevation angle are non-zero, the tilt angle and / or elevation angle are subtracted from the vertical scan angle to obtain the vertical detection angle. For example, if the vertical scan angle is 40°, the lidar system 102 is mounted with a 10° upward tilt, and the vehicle 100 is traveling uphill or downhill on a 15° slope (i.e., -15° elevation angle), the vertical detection angle is determined to be 40° - 10° - (-15°) = 45°.

[0051] In some embodiments, the detection distance can be calculated differently for two ranges of vertical detection angles: a first range [0, θa], where θa is the threshold angle, and a second range [θa, 90°]. In some embodiments, the threshold angle θa can be determined according to equation (1):

[0052]

[0053] Where h0 is the height of the lidar system 102 above the ground, and d max That is the maximum detection range.

[0054] When the vertical detection angle (e.g., as Figure 5 When the top-down angle θ is less than θa (i.e., within the first range), the detection distance remains d. max When the viewing angle θ is greater than θa (i.e., within the second range), the detection distance d θ The detection distance decreases. In some embodiments, equation (2) can be used to determine the detection distance:

[0055]

[0056] Based on the determined detection range, the gain determination unit 444 can calculate the target gain of the detector 216. In some embodiments, for a target gain greater than the maximum detection range d... max Short detection range d θ(That is, for a vertical detection angle θ greater than the threshold angle θa), the gain determination unit 444 can adjust the detector gain from the maximum gain G. max Reduced 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 the ratio of the first reflectivity of the target object to the second reflectivity of the ground. For example, the gain determination unit 444 can calculate the target gain (G) of the downward angle θ according to equation (3). θ ):

[0057]

[0058] Among them, G max It is the maximum gain of detector 216, ρ object It is the reflectivity of the target object, ρ ground It is the reflectivity of the ground, d θ The detection range is the top angle θ, d max This is the maximum detection range. In some embodiments, the reflectivity of the ground can be predetermined and pre-programmed into the controller 206. In some embodiments, the reflectivity of the target object (e.g., object 112) can be dynamically determined based on the returned laser beam signal received in real time by the receiver 204.

[0059] In some embodiments, the target gain G corresponds to each vertical detection angle θs of the beam. θs The calculations can be performed offline according to equations (1)-(3), for example, via a separate processor. The mapping between the target gain and the vertical detection angle can be recorded in a lookup table and pre-programmed in the controller 206. For example, the lookup table can be stored in the memory 406 or storage 408 of the controller 206. According to such an embodiment, the calculations performed by the detection distance determination unit 442 described above can be skipped. The gain determination unit 444 can determine the target gain by looking up the vertical detection angle θ in the lookup table.

[0060] In some embodiments, the saturation detection unit 446 can determine whether a saturation condition has occurred based on the detection results provided by the saturation detection circuit 310. In some embodiments, if a saturation condition is detected, the saturation detection unit 446 can further determine where the saturation condition occurs, for example, in the photodetector 302, the signal amplifier 304, and / or the signal conditioning circuit 306.

[0061] The command signal generation unit 448 can generate a command signal based on the determinations of the gain determination unit 444 and / or the saturation detection unit 446 to adjust the gain of the detector 216. In some embodiments, when using open-loop control, the command signal can be generated based on the target gain determined by the gain determination unit 444 to adjust the gain of the detector 216 to the target gain. Figure 6 The open-loop control method is described in more detail. In some alternative embodiments, when using closed-loop control, a command signal can be generated upon detection of a saturation condition to reduce the gain of detector 216 until the gain decreases to a level where the saturation condition no longer exists. This will be combined with... Figure 7 The closed-loop control method is described in more detail. In some alternative embodiments, a hybrid control method 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 disappears from the detector 216.

[0062] In some embodiments, the command signal can adjust the gain of one or more stages in detector 216. For example, the command signal can adjust the bias voltage of photodetector 302, and / or the gain of signal amplifier 304 and / or signal conditioning circuit 306. In some embodiments, based on the location where the saturation condition occurs as determined by saturation detection unit 446, the command signal can be provided to the corresponding component to adjust its gain and eliminate the saturation condition.

[0063] Figure 6 This is a flowchart of an exemplary open-loop control method 600 for adjusting the receiver gain of a lidar system according to embodiments of this specification. In some embodiments, method 600 may be performed by various components of the lidar system 102, such as receiver 204 and controller 206. In some embodiments, method 600 may include steps S602-S618. It should be understood that some steps may be optional. Furthermore, some steps may be performed simultaneously or in conjunction with... Figure 6 The different execution orders shown.

[0064] In step S602, controller 206 may determine the vertical detection angle of the current scan angle. In some embodiments, controller 206 may receive the current scan angle used by transmitter 202. In some embodiments, controller 206 may be the same controller that determines the scan parameters and thus stores the parameters in its memory / storage. Therefore, controller 206 can retrieve the scan angle from its own memory / storage. Otherwise, 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 traveling on the slope.

[0065] In step S604, the controller 206 can calculate the detection distance corresponding to the current vertical detection angle. For example, when the vertical detection angle θ is less than, for example, a threshold angle θa calculated according to equation (1), the detection distance determination unit 342 can determine that the detection distance remains at the maximum detection distance d. max When the angle θ exceeds θa, the detection distance determination unit 342 can use trigonometric functions of the height h0 and the angle θ (e.g., according to equation (2)) to determine the detection distance.

[0066] In step S606, the controller 206 may determine the detector gain for receiving the beam emitted at the current scanning angle based on the detection distance determined in step S604. In some embodiments, for a maximum detection distance d... max Short detection range d θ The gain determination unit 444 can determine the gain from the maximum gain G. max Reduced to a smaller but sufficient level. In some embodiments, the target gain may be proportional to the square of the respective detection range. In some further embodiments, the transmit power level is proportional to the 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).

[0067] In step S608, the controller 206 may generate a command signal corresponding to the target gain determined in step S606. In some embodiments, the 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 S610, the controller 206 may provide the command signal to the corresponding component of the detector 216, thereby adjusting the gain to the target gain.

[0068] In step S612, receiver 204 can use detector 216 to detect the beam of light returned by the target object. For example, receiver 204 can detect the returned laser beam 211 returning from object 212. Receiver 204 can collect the laser beam returning from object 212 and adjust the output electrical signal reflecting the intensity of the returned laser beam according to the gain. In step S614, controller 206 can determine the reflectivity of the target object based on the intensity of the returned laser beam. In step S606, the reflectivity of the object can be used to determine the target gain. For example, the target gain can be further adjusted by the ratio of the reflectivity of the target object to the reflectivity of the ground.

[0069] In step S616, controller 206 can determine whether all scanning angles of scanner 210 have been covered. If not (S616: No), method 600 proceeds to step S618, for example, by repeating steps S602-S616 to determine and adjust the detector gain for the next scanning angle. Method 600 ends after scanner 210 has covered all scanning angles (S616: Yes).

[0070] In some embodiments, steps S604-S606 can be performed offline for all vertical detection angles to determine the corresponding target gain. The result can be recorded in a lookup table and saved along with the controller 206. In real-time execution, method 600 can skip S604 and S606; instead, method 600 can include the step of the controller 206 looking up the target gain corresponding to the current vertical detection angle from a predetermined lookup table. By using a lookup table, computational costs can be significantly reduced.

[0071] Figure 7 This is a flowchart of an exemplary closed-loop control method 700 for adjusting the receiver gain of a lidar system according to embodiments of this specification. 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 steps S702-S714. It should be understood that some steps may be optional. Furthermore, some steps may be performed simultaneously or in conjunction with... Figure 7 The different execution orders shown.

[0072] In step S702, the controller 206 can detect the saturation state of the detector 216 based on the detection results provided by the saturation detection circuit 310. In some embodiments, if a saturation condition is detected, the controller 206 can further determine where the saturation condition occurs, for example, in the photodetector 302, the signal amplifier 304, and / or the signal conditioning circuit 306.

[0073] In step S704, controller 206 may generate a command signal to reduce the gain of detector 216. In some embodiments, to reduce the overall gain of detector 216, a command signal may be generated to adjust the bias voltage of photodetector 302 and / or the gain of signal amplifier 304 and / or signal conditioning circuit 306. In step S706, controller 206 may provide command signals to the individual components of detector 216 to adjust the gain to a target gain.

[0074] In step S708, receiver 204 can use detector 216 to detect the beam returned by the target object. In step S710, controller 206 can determine whether the saturation condition has disappeared. Reducing the gain of detector 216 helps reduce the electrical signal generated by detector 216, thereby keeping detector 216 outside the saturation region. If the saturation condition has not disappeared (S710: No), 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), method 700 can proceed to step S712, where controller 206 determines whether all scanning angles of scanner 210 have been covered. If not (S712: No), method 700 proceeds to step S714, for example, by repeating steps S702-S712 to adjust the detector gain for the next scanning angle. Method 700 ends after scanner 210 has passed all scanning angles (S712: Yes).

[0075] In some embodiments, the hybrid control method can be implemented by combining certain steps of method 600 and method 700. For example, for each scan angle, controller 206 may first perform open-loop control steps S602-S614 to adjust the gain to a determined target gain. Then, controller 206 may perform closed-loop control steps S702-S710 to fine-tune the gain to ensure that there is no saturation condition.

[0076] In some embodiments, the systems and methods described in this current disclosure may be combined with those described in U.S. Application No. 16 / 920650, which is incorporated herein by reference. For example, the transmitter power level and receiver gain may be adjusted to jointly compensate for variations in the detection range of the lidar system at different vertical detection angles.

[0077] Although this specification uses a lidar system as an example, the disclosed embodiments can be adapted and implemented as other types of optical sensing systems that use a receiver to receive light signals, not limited to laser beams. For example, the embodiments can be readily adapted to optical imaging systems or radar detection systems that use electromagnetic waves to scan objects.

[0078] Another aspect of this specification relates to a non-transitory computer-readable medium storing instructions that, when executed, cause one or more processors to perform the methods described above. The computer-readable medium may include volatile or non-volatile, magnetic, semiconductor-based, magnetic tape-based, optical, removable, non-removable, or other types of computer-readable media or computer-readable storage devices. For example, as disclosed, a computer-readable medium may be a storage device or memory module on which computer instructions are stored. In some embodiments, the computer-readable medium may be a disk or flash drive on which computer instructions are stored.

[0079] It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed system and related methods. Other embodiments will become apparent to those skilled in the art upon consideration of the specification and practice of the disclosed system and related methods.

[0080] This specification and the embodiments are to be considered exemplary only, and the true scope is indicated by the following claims and their equivalents.

Claims

1. An optical sensing system, comprising: A transmitter configured to emit a light beam at multiple vertical detection angles to scan an object; A receiver, the receiver including a detector configured to detect a beam of light reflected back by the object; as well as A controller configured to dynamically change the gain of the detector used to detect the light beam at various vertical detection angles, including: For each vertical detection angle, the gain of the detector is reduced when the vertical detection angle exceeds a threshold angle; wherein the threshold angle is determined based on the elevation angle of the optical sensing system located above the ground and the threshold detection distance of the optical sensing system, and the threshold detection distance is the horizontal distance between the object and the optical sensing system.

2. The optical sensing system as described in claim 1, wherein, The controller is configured to change the gain of the detector based on a predetermined lookup table, which maps the respective vertical detection angles to the target detector gain.

3. The optical sensing system as described in claim 2, wherein, The gain of the target detector is proportional to the square of its respective detection distance, which is determined based on the elevation angle of the optical sensing system located above the ground and its respective vertical detection angle.

4. The optical sensing system as described in claim 2, wherein, The controller is also configured to: The first reflectivity of the object is determined based on the light beam received by the receiver; and The gain of the detector is adjusted by the ratio of the first reflectivity to the second reflectivity of the ground.

5. The optical sensing system of claim 2, further comprising a saturation detection circuit configured to detect the saturation condition of the detector, wherein, The controller is further configured to fine-tune the gain of the detector until the saturation condition disappears.

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

7. The optical sensing system as described in claim 6, wherein, The detector includes a photodetector, a signal amplifier, and a signal conditioning circuit, wherein the controller is configured such that the saturation detection circuit detects a saturation condition from the photodetector, the signal amplifier, or the signal conditioning circuit, and reduces the gain of the photodetector, the signal amplifier, or the signal conditioning circuit.

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

9. The optical sensing system as claimed in claim 1, wherein, The detector includes a signal amplifier configured to amplify an electrical signal generated in response to receiving the light beam at each of the respective vertical detection angles, wherein the controller is further configured to change the gain of the signal amplifier in order to dynamically change the gain of the detector.

10. The optical sensing system as claimed in claim 1, wherein, The detector includes a signal conditioning circuit configured to adjust an electrical signal generated in response to receiving the light beam at each of the respective vertical detection angles, wherein the controller is further configured to change the gain of the signal conditioning circuit in order to dynamically change the gain of the detector.

11. The optical sensing system as claimed in claim 1, wherein, The optical sensing system is a light detection and ranging (LiDAR) system.

12. A method for controlling the gain of a receiver in an optical sensing system, comprising: The transmitter emits beams at multiple vertical detection angles to scan objects; The beam of light returned by the object is detected by a detector in the receiver; as well as The gain of the detector used to detect the beam at various vertical detection angles is dynamically changed by the controller, including: For each vertical detection angle, the gain of the detector is reduced when the vertical detection angle exceeds a threshold angle; wherein the threshold angle is determined based on the elevation angle of the optical sensing system located above the ground and the threshold detection distance of the optical sensing system, and the threshold detection distance is the horizontal distance between the object and the optical sensing system.

13. The method of claim 12, wherein, The detector gain is dynamically changed based on a predetermined lookup table, which is used to map the various vertical detection angles to the target detector gain.

14. The method of claim 13, wherein, The gain of the target detector is proportional to the square of its respective detection distance, which is determined based on the elevation angle of the optical sensing system located above the ground and its respective vertical detection angle.

15. The method of claim 13, wherein, Dynamically changing the gain of the detector also includes: The saturation condition of the detector is detected by a saturation detection circuit; and The gain of the detector is fine-tuned by the controller until the saturation condition disappears.

16. The method of claim 12, wherein, Dynamically changing the gain of the detector further includes reducing the gain of the detector when the saturation detection circuit detects saturation of the detector when receiving the beam at the vertical detection angle.

17. The method of claim 12, wherein, The detector includes a photodetector configured to generate an electrical signal in response to receiving the light beam at the respective vertical detection angles, wherein dynamically changing the gain of the detector further includes changing the bias voltage of the photodetector.

18. A receiver in an optical sensing system, comprising: A detector configured to detect a beam of light returned by an object that has been scanning by emitting beams at multiple vertical detection angles; as well as A controller configured to dynamically change the gain of the detector based on a predetermined lookup table that maps each vertical detection angle to the gain of the target detector, including: For each vertical detection angle, the gain of the detector is reduced when the vertical detection angle exceeds a threshold angle; wherein the target detector gain is proportional to the square of the detection distance determined based on the elevation angle of the optical sensing system above the ground and the respective vertical detection angle, the threshold angle is determined based on the elevation angle of the optical sensing system above the ground and the threshold detection distance of the optical sensing system, the threshold detection distance being the horizontal distance between the object and the optical sensing system.

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