Increased Dynamic Range of a Time-of-Flight (ToF) Lidar System

Abstract

This document describes techniques and systems for increasing the dynamic range of a time-of-flight (ToF) lidar system. The described lidar system adjusts the bias voltage of a photodetector for other return pulses of an object pixel based on the energy of a first return pulse. For highly reflective or short-range objects, the bias voltage can be lowered. Similarly, for low-reflectivity or long-range objects, the bias voltage can be increased. The ability of the described lidar system to adjust the bias voltage of the photodetector for each object pixel increases the dynamic range of the lidar system without additional hardware or complex readings. The increased dynamic range allows the described lidar system to maintain long-range capabilities while accurately measuring the return pulse intensity for detecting short-range or highly reflective objects.

Description

Background Art

[0001] Automotive lidar systems use laser signals to determine the speed and distance of stationary and moving objects (such as other vehicles, pedestrians, obstacles). The lidar system compares the transmitted signal that is emitted with the returned signal that is reflected to make these measurements. For long-range applications, it is desirable to increase the dynamic range of the lidar system. Specifically, a larger dynamic range allows the lidar system to increase its low-light detection ability while maintaining accurate reflectivity measurements for near-range objects. Especially for time-of-flight lidar systems, increasing the dynamic range may require more complex and expensive hardware and processing capabilities. Summary of the Invention

[0002] This document describes techniques and systems for increasing the dynamic range of a time-of-flight (ToF) lidar system. The described lidar system adjusts the bias voltage of a photodetector for other return pulses of an object pixel based on the energy of a first return pulse. For a highly reflective or near-range object, the bias voltage can be turned down. Similarly, for a low-reflectivity or long-range object, the bias voltage can be increased. The ability of the described lidar system to adjust the bias voltage of the photodetector for each object pixel increases the dynamic range of the lidar system without additional hardware or complex readout. The increased dynamic range allows the described lidar system to maintain long-range capabilities while accurately measuring the return pulse intensity for detecting near-range objects or highly reflective objects.

[0003] For example, this document describes transceiver functionality for increasing the dynamic range of a ToF lidar system. The described transceiver emits at least two pulses for each object pixel within the field of view of the lidar system. The energy of the first pulse is lower than the energy of the other pulses among the at least two pulses for each object pixel. The system receives at least two return pulses. The return pulses are reflections of the emitted pulses. Based on the energy of the first return pulse, the transceiver adjusts the bias voltage of its photodetector before receiving the other return pulses of the object pixel. The transceiver outputs the return pulses obtained by the photodetector to the processor of the lidar system.

[0004] This document also describes apparatuses for performing the methods of the systems outlined above and other methods set forth herein, as well as the methods performed by these lidar systems.

[0005] This summary introduces a simplified concept of the increased dynamic range of a ToF lidar system, which is further described below in the detailed embodiments and the drawings. This summary is not intended to identify the essential features of the claimed subject matter, nor is it intended to be used to determine the scope of the claimed subject matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Details of one or more aspects of increasing the dynamic range of a ToF lidar system are described with reference to the following drawings in this document. Like reference numerals are generally used throughout the drawings to refer to like features and components:

[0007] Figure 1 An example environment is shown in which a ToF lidar system with an increased dynamic range can be implemented;

[0008] Figure 2 An example implementation of a ToF lidar system as part of a vehicle is shown;

[0009] Figure 3-1 An example operation of a ToF lidar system with an increased dynamic range is shown;

[0010] Figure 3-2 Object pixels scanned by a ToF lidar system during a frame are shown;

[0011] Figure 4 An example receiver, intensity readout module, and processor of the described lidar system are shown;

[0012] Figure 5 An example environment in which the receiver and intensity readout module of the described lidar system operate is shown; and

[0013] Figure 6 An example method performed by a ToF lidar system with an increased dynamic range is shown. DETAILED DESCRIPTION

[0014] OVERVIEW

[0015] Automotive lidar systems are important sensing technologies, and some vehicle-based systems rely on them to obtain critical information about the surrounding environment. A lidar system has a field of view, which represents a volume of space within which the lidar system looks for nearby objects. The field of view consists of a large number of object pixels (e.g., one million object pixels). The time it takes for a lidar system to scan each object pixel within the field of view (e.g., collect information for all object pixels) is one frame. By scanning each object pixel in a sequence of frames, a ToF lidar system can determine the range and reflectivity information of nearby objects.

[0016] A ToF lidar system scans each object pixel by emitting one or more laser pulses and detecting the reflections of the one or more pulses. The dynamic range of the system represents the ability of the lidar system to accurately process the reflected return signals from objects at short range and objects at long range, or objects with high reflectivity and objects with low reflectivity. It is typically measured as the ratio between the maximum and minimum energies received by the lidar system that produces an accurate output. Many automotive applications require lidar systems with a large dynamic range. For example, a larger dynamic range can improve the low-light detection ability of the lidar system (e.g., for distant or low-reflectivity objects), while maintaining accurate measurements in the case of short range or high reflectivity. However, increasing the dynamic range increases the hardware cost or readout complexity of the lidar system.

[0017] Some lidar systems include at least two photodetectors (e.g., sensors) with different sensitivities to increase the dynamic range. The lidar system includes a first set of photodetectors with relatively high sensitivity and a second set of photodetectors with lower sensitivity. The readout of these lidar systems includes data from multiple types of photodetectors. In addition to the cost associated with multiple types of photodetectors, the output of these lidar systems is more complex and requires additional signal processing.

[0018] Other lidar systems use complex systems to adjust the bias voltage of the photodetectors to increase the dynamic range. In one such system, the photodetectors operate in different modes by adjusting the bias voltage. In another system, the bias voltage of the photodetectors is adjusted proportionally based on the time of flight between the emission of the transmitted signal and the reception of the return signal. Each of these systems can increase the dynamic range of the lidar system, but requires additional hardware, a high-bandwidth power controller, and a complex readout to achieve this result.

[0019] Compared with those lidar systems, this document describes techniques and systems for increasing the dynamic range of a lidar system without adding additional hardware and / or complex readout. The described lidar system includes a transmitter configured to emit at least two pulses for each object pixel. The energy of the first pulse among the at least two pulses is less than the peak output of the other pulses for the same object pixel. The lidar system also includes a receiver configured to receive at least two return pulses that are reflections of the transmitted pulses. The receiver is configured to: adjust the bias voltage of a photodetector for the other return pulses of the object pixel based on the energy of the first return pulse. Subsequently, output the return pulses. By dynamically adjusting the bias voltage of the photodetector on a per-object-pixel basis based on the energy of the first return pulse, the described lidar system has an increased dynamic range without the need for additional hardware or complex readout. With the increased dynamic range, a ToF lidar system can provide lidar data for a vehicle system (e.g., a collision avoidance system) for objects in the surrounding environment at greater distance ranges and reflectivities.

[0020] This is just one example of how the described techniques and systems increase the dynamic range of a ToF lidar system. This document describes other examples and implementations.

[0021] Operating Environment

[0022] Figure 1 An example environment 100 is shown where techniques using a ToF lidar system 102 with an increased dynamic range and an apparatus including the ToF lidar system 102 with an increased dynamic range can be implemented. The ToF lidar system 102 may be referred to simply as "lidar system 102". In the depicted environment 100, the lidar system 102 is mounted to a vehicle 104 or integrated within the vehicle 104. The lidar system 102 is capable of detecting one or more objects 108 in the area near the vehicle 104. Although shown as an automobile, the vehicle 104 may represent other types of motor vehicles (e.g., motorcycles, buses, tractors, semi-trailers, or construction equipment), non-motor vehicles (e.g., bicycles), rail vehicles (e.g., trains or trams), watercraft (e.g., boats or ships), aircraft (e.g., airplanes or helicopters), or spacecraft (e.g., satellites). In some cases, the vehicle 104 may tow or include a trailer or other attachments. Generally, a manufacturer may mount the lidar system 102 to any mobile platform, including mobile machinery or robotic devices.

[0023] In the depicted implementation, lidar system 102 is mounted on top of vehicle 104 and provides a field of view 106 that illuminates object 108. Lidar system 102 divides the field of view 106 into object pixels (as Figure 3-2 shown). Lidar system 102 can project the field of view 106 from any exterior surface of vehicle 104. For example, a vehicle manufacturer can integrate lidar system 102 into a bumper, side mirror, or any other interior or exterior location that requires detecting the distance or classification of object 108. In some cases, vehicle 104 includes multiple lidar systems 102, such as a first lidar system 102 and a second lidar system 102 that together provide a larger field of view 106. Generally, a vehicle manufacturer can design the location of one or more lidar systems 102 to provide a specific field of view 106 that encompasses an area of interest where object 108 may be present. Example fields of view 106 include a 360-degree field of view, one or more 180-degree fields of view, one or more 90-degree fields of view, etc., which can overlap or be combined into a field of view 106 of a specific size.

[0024] Object 108 is composed of one or more materials that reflect lidar signals. Depending on the application, object 108 can represent a target of interest. In some cases, object 108 is a moving object 110, such as another vehicle 110-1, semi-trailer 110-2, person 110-3, animal 110-4, bicycle 110-5, or motorcycle 110-6. In other cases, object 108 represents a stationary object 112, such as a traffic cone 112-1, concrete barrier 112-2, guardrail 112-3, fence 112-4, tree 112-5, or parked vehicle 112-6. Stationary objects 112 can be continuous (e.g., concrete barrier 112-2, guardrail 112-3) or discontinuous (e.g., traffic cone 112-1) along a portion of the road.

[0025] The lidar system 102 represents a time-of-flight lidar system that emits and receives lidar signals, which include pulses for each object pixel in the field of view 106. The lidar system 102 measures the distance to the object 108 based on the time it takes for the pulses to travel from the lidar system 102 to the object 108 and back to the lidar system 102. The lidar system 102 can also measure the reflection properties of the object 108 based on the energy of the received pulses. Information about this energy can be used to classify the object 108. As an example, the lidar system 102 can determine whether the object 108 is a parked vehicle 112-6, a lane marker, a road surface, or a person 110-3. The energy information also enables the lidar system 102 to determine the characteristics of the object 108, such as the material composition of the object 108. Relative to Figure 2 The lidar system 102 and the vehicle 104 are further described.

[0026] Figure 2 The lidar system 102 is shown as part of the vehicle 104. The vehicle 104 also includes at least one vehicle-based system 202, and at least one vehicle-based system 202 depends on data from the lidar system 102. Systems 202 such as the driver assistance system 204 and the autonomous driving system 206. Generally, the vehicle-based system 202 uses the lidar data provided by the lidar system 102 to perform functions. For example, the driver assistance system 204 provides blind spot monitoring and generates an alert that indicates a potential collision with the object 108 detected by the lidar system 102. In this case, the lidar data from the lidar system 102 indicates when it is safe or unsafe to change lanes.

[0027] As another example, the driver assistance system 204 suppresses an alert in response to the lidar system 102 that indicates that the object 108 represents a stationary object 112 (such as a road barrier). In this way, the driver assistance system 204 can avoid annoying the driver with an alert when the vehicle 104 is driving next to a road barrier. Suppressing the alert may also be beneficial in cases where reflections from the road barrier generate false detections of what appears to be a moving object. By suppressing the alert, these false detections will not cause the driver assistance system 204 to warn the driver.

[0028] The autonomous driving system 206 can move the vehicle 104 to a specific position on the road while avoiding collisions with other objects 108 detected by the lidar system 102. The lidar data provided by the lidar system 102 can provide information related to the distance and reflectivity of the objects 108, enabling the autonomous driving system 206 to perform emergency braking, execute a lane change, or adjust the speed of the vehicle 104.

[0029] The lidar system 102 includes a communication interface 208 to transmit lidar data to the vehicle-based system 202 or another component of the vehicle 104. For example, when the individual components of the lidar system 102 are integrated within the vehicle 104, the communication interface 208 can transmit data via the communication bus of the vehicle 104. Generally, the lidar data provided by the communication interface 208 is in a format usable by the vehicle-based system 202. In some implementations, the communication interface 208 can send information to the lidar system 102, such as the speed of the vehicle 104, or whether the turn indicator is on or off. The lidar system 102 uses this information to configure itself appropriately. For example, the lidar system 102 can adjust its frame rate or scan speed based on the speed of the vehicle 104. Alternatively, the lidar system 102 can dynamically adjust the field of view 106 based on whether the right turn indicator or the left turn indicator is on.

[0030] The lidar system 102 also includes a transmitter 210 for emitting lidar signals and a receiver 212 for receiving the reflected versions of these lidar signals. The transmitter 210 includes elements (whether optical or otherwise) for emitting lidar signals, as well as associated components for directing the lidar signals. The transmitter 210 can form steered or un-steered, wide or narrow beams. Steering and shaping can be achieved through analog beamforming or digital beamforming. The receiver 212 includes one or more arrays of photodetectors (collectively referred to as photodetectors) to detect the reflected lidar signals. The photodetectors can be implemented as silicon photomultipliers (SiPMs), avalanche photodiodes (APDs), single-photon avalanche diodes (SPADs), photomultiplier tubes (PMTs), or PIN diodes. A PIN diode includes an undoped intrinsic semiconductor region located between a p-type and an n-type semiconductor region. The transmitter 210 and the receiver 212 can be incorporated together on the same integrated circuit (e.g., a transceiver integrated circuit) or separately on different integrated circuits.

[0031] The lidar system 102 also includes one or more processors 216 and a computer-readable storage medium (CRM) 218. The processor 216 can be implemented as a microprocessor or a system-on-chip. The processor 216 executes instructions stored within the CRM 218. As an example, the processor 216 can determine ( Figure 1 of) the position of the object 108 relative to the lidar system 102 (e.g., determine the slant range, azimuth angle, and elevation to the object 108), determine the material composition of the object 108, or classify the object 108. Generally, the processor 216 determines the characteristics of the object 108 based on the information provided by the receiver 212. The processor 216 also generates lidar data for the vehicle-based system 202.

[0032] The lidar system 102 also includes an intensity readout module 214. The intensity readout module 214 provides an interface between the receiver 212 and the processor 216. In some implementations, the intensity readout module 214 is incorporated within the receiver 212 and implemented on the same integrated circuit. However, the intensity readout module 214 can be separated from the receiver 212 and implemented on a different integrated circuit (or multiple integrated circuits), and in some implementations, at least a portion of the intensity readout module 214 can be implemented by the processor 216.

[0033] Generally, the intensity readout module 214 extracts information from the analog signal output by the receiver 212 and generates digital information for the processor 216. The intensity readout module 214 also includes means for controlling the bias voltage of the photodetector within the receiver 212.

[0034] The lidar system 102 can include a timing readout module (not shown) that generates timing data related to the time-of-flight of the return signal. For example, the timing readout module can determine the time associated with when the voltage or current of a pulse in the return signal is greater than, equal to, or less than a threshold.

[0035] Figure 3-1 An example operation of the lidar system 102 with an increased dynamic range is shown. In Figure 3-1 the environment 300, the objects 108-11 and 108-21 (collectively referred to as the object 108) are located at a specific distance and angle from the lidar system 102. To detect the object 108, the lidar system 102 emits transmit signals 302 for each object pixel in the object pixels 306.

[0036] For reference, Figure 3-2Shows object pixels 306 of the field of view 106 scanned by lidar system 102 during a frame (not shown). The field of view 106 includes object pixels 306-11, 306-21, 306-31, …, 306-X1, …, 306-XY, 306-3Y, 306-2Y, 306-1Y, and all other object pixels scanned during that frame. The object pixels 306 are shown arranged in a grid that is X pixels wide by Y pixels high and are scanned individually in the order indicated by the arrows, one row (or column) at a time, but other orders for scanning the object pixels 306 are possible.

[0037] Return reference Figure 3-1 , for each object pixel 306, the transmitted signal 302 includes a plurality of pulses 308, such as pulses 308-1 to 308-N in a pulse train, where N represents a positive integer. The energy of the first pulse 308-1 (e.g., the intensity or power level of the pulse) is lower than the energy of the other pulses 308-2 to 308-N in the pulse train. The energy of the first pulse 308-1 can be, for example, a fraction or percentage (e.g., twenty, thirty, forty, or fifty percent) lower than the energy of the other pulses 308-2 to 308-N, which can be used to detect low-reflectivity or distant objects. The energy of the first pulse 308-1 can be based on the sensitivity of the photodetector or the desired range of the lidar system 102. Additionally, the lidar system 102 can customize the number of pulses 308 and the transmission characteristics of the pulses 308 (e.g., pulse width, time interval between each pulse 308, energy level) for each transmitted signal 302 in the transmitted signals 302 to achieve a specific scan speed, detection range, or distance resolution.

[0038] In the depicted example, the lidar system 102 transmits transmitted signals 302-11 and 302-21 in object pixels 306-11 and 306-21, respectively. The transmitted signals 302-11 and 302-21 are collectively referred to as the transmitted signal 302. The lidar system 102 scans the object pixels 306 within the field of view 106 in sequence. A frame (not shown) represents the time taken to scan all individual object pixels 306 within the field of view 106.

[0039] Object 108-11 reflects at least a portion of the transmitted signal 302-11. The reflected portion represents the return signal 304-11. The lidar system 102 receives the return signal 304-11 and processes the return signal 304-11 to extract lidar data related to object 108-11 of the vehicle-based system 202. As depicted, due to losses incurred during propagation and reflection, the amplitude of the return signal 304-11 is less than the amplitude of the transmitted signal 302-11.

[0040] Similarly, object 108-21 reflects at least a portion of the transmitted signal 302-21. The return signals 304-11 and 304-21 are collectively referred to as the return signal 304. The lidar system 102 receives the return signal 304-21 and processes the return signal 304-21 to extract lidar data related to the object 108-21 of the vehicle-based system 202.

[0041] In the depicted example, the amplitude of the return signal 304-21 is greater than the amplitude of the return signal 304-11. The amplitude difference of the return signal 304 may be due to the distance of the object 108 from the lidar system 102 or the reflectivity of the object 108. As an example, the object 108-21 is closer to the lidar system 102 than the object 108-11 and the objects 108-11 and 108-21 have similar reflectivities. As another example, the objects 108-11 and 108-21 may be located at approximately the same distance from the lidar system 102, and the amplitude of the return signal 304-21 is greater than the amplitude of the return signal 304-11 because the reflectivity of the object 108-21 is higher than the reflectivity of the object 108-11.

[0042] At the lidar system 102, the return signals 304-11 and 304-21 respectively represent delayed versions of the transmitted signals 302-11 and 302-21. The amount of delay is proportional to the range (e.g., distance) from the objects 108-11 and 108-21 to the lidar system 102. For example, the delay represents the time it takes for the transmitted signal 302-11 to propagate from the lidar system 102 to the object 108-11 and for the return signal 304-11 to travel back to the lidar system 102. Like the transmitted signal 302, the return signal 304 includes a plurality of pulses 308. Regarding Figure 4 The reception and processing of the return signal 304 by the lidar system 102 are described in more detail.

[0043] Figure 4 An example receiver 212, intensity readout module 214, and processor 216 of the lidar system 102 are shown. In the depicted configuration, the intensity readout module 214 is coupled between the receiver 212 and the processor 216.

[0044] The receiver 212 includes at least one photodetector 402. Although not explicitly shown, the receiver 212 may include other elements, such as an amplifier.

[0045] The photodetector 402 detects the reflected return signal 304 by collecting the photons contained in the pulse 308. The photodetector 402 converts the photons into an analog current. In the case where the photodetector 402 is an APD, SiPM, or SPAD array, the photodetector 402 pulls the electrons generated by photon absorption towards the multiplication region, where the photon-induced electrons are amplified to produce a breakdown avalanche of multiplied electrons. In the linear output region of the photodetector 402, the output of the photodetector increases linearly based on the number of incident photons in the pulse 308. As the number of photons incident on the photodetector 402 increases, the output of the photodetector becomes non-linear and is not proportional to the number of received photons. In the non-linear region of the photodetector 402, since the lidar system 102 may not be able to determine the time-of-flight or intensity information of the return signal 304, the accuracy of distance determination and reflectivity determination performed by the lidar system 102 is reduced. Generally, the non-linear region of the photodetector 402 begins at approximately seventy percent of the maximum incident energy capacity of the photodetector 402.

[0046] The sensitivity of the photodetector 402 to the photons in the return signal 304 can be adjusted by its bias voltage. An increase in the bias voltage increases the sensitivity of the photodetector 402 to the return signal 304 with low energy (e.g., reflected by an object 108 that is far from the lidar system 102 or has a low reflectivity). Similarly, a decrease in the bias voltage reduces the sensitivity of the photodetector 402 to the return signal with high energy.

[0047] The intensity readout module 214 extracts information from the analog current output output by the receiver 212 and generates digital information for the processor 216. As described above with respect to Figure 2 the intensity readout module 214 can be incorporated as part of the receiver 212 or implemented as a separate component in the lidar system 102. The intensity readout module 214 includes a hold circuit 406 and an analog-to-digital converter 408. The intensity readout module 214 may also include a low-pass filter 404.

[0048] The low-pass filter 404 can be coupled between the receiver 212 and the hold circuit 406 or between the hold circuit 406 and the analog-to-digital converter 408. The low-pass filter 404 attenuates high-frequency noise. By attenuating the noise, the low-pass filter 404 improves the measurement accuracy of the lidar system 102.

[0049] The hold circuit 406 is coupled between the receiver 212 and the analog-to-digital converter 408. The hold circuit 406 samples the analog signal. Specifically, the hold circuit 406 holds the analog signal for a specified duration and samples the signal. The hold duration and sampling rate of the hold circuit 406 can be pre-programmed or controlled by the processor 216. The hold circuit 406 can be implemented as, for example, an integrate-and-hold circuit, or a peak-and-hold circuit. The integrate-and-hold circuit measures the amount of charge within the pulse 308 (e.g., measures the amount of current or voltage that changes over time) and generates a voltage representative of the energy of the pulse 308. The peak-and-hold circuit measures the peak amplitude of the current or voltage across the pulse 308 and generates a voltage representative of the energy of the pulse 308.

[0050] The analog-to-digital converter 408 is coupled between the hold circuit 406 and the processor 216. The analog-to-digital converter 408 collects one or more samples of the output voltage from the hold circuit 406 and generates intensity data 412 that indicates the energy of the pulse 308. The intensity data 412 represents the amount of photon downscaling received by the photodetector 402 within the pulse 308 of the return signal 304. The intensity data 412 can be output to the processor 216 as a consolidated signal for each of the pulses 308 in the object pixel 306. For example, the intensity data 412 can be collected by the analog-to-digital converter 408 or another component of the intensity readout module 214 (such as a buffer) as a consolidated signal for the pulses 308-1 to 308-N of the object pixel 306-11, and then the intensity data 412 is sent to the processor 216 once the intensity data for each of the pulses 308 of the object pixel 306-11 has been collected.

[0051] The processor 216 analyzes the intensity data 412 associated with the pulses 308-1 to 308-N to detect the object 108. The processor 216 can use the intensity data 412-1 to 412-N to determine the material composition of the object 108 and / or classify the object 108. Additionally, the processor 216 can use the timing data obtained from the pulse data 410 to measure the distance between the lidar system 102 and the object 108. Information related to the distance and classification of the object 108 can be provided as lidar data 416 to Figure 2 the vehicle-based system 202.

[0052] A controller (not shown) of the intensity readout module 214 can control the bias voltage of the photodetector 402. The controller can be implemented using hardware, software, firmware, or a combination thereof in the intensity readout module 214. In other cases, the controller can be included within the photodetector 402 or the receiver 212. The controller generates a bias control signal 414, which is provided to the receiver 212. In this way, the bias voltage of the photodetector 402 can be dynamically adjusted by the controller based on the energy of the first pulse 308-1 of each object pixel 306.

[0053] During operation, the receiver 212 receives the return signal 304 and provides it to the photodetector 402. The return signal 304 includes a plurality of pulses 308, such as pulses 308-1 to 308-N. The photodetector 402 converts the photons in the pulses 308 into pulse data 410. The pulse data 410 represents the analog current response of the photodetector 402 to the pulses 308 in the time domain.

[0054] The pulse data 410 can be filtered by the low-pass filter 404. The pulse data 410 or the filtered pulse data 418 is input to the hold circuit 406. The hold circuit 406 samples the pulse data 410 or the filtered pulse data 418 and outputs sampled pulse data 420. The analog-to-digital converter 408 converts the sampled pulse data 420 into digital intensity data 412.

[0055] Based on the intensity data 412, the bias control signal 414 can be provided to the receiver 212. The bias control signal 414 instructs the receiver 212 to increase or decrease the bias voltage of the photodetector 402 for subsequent pulses 308-2 to 308-N of the object pixel 306 (e.g., object pixel 306-11), as described in more detail with reference to Figure 5 The bias voltage of the photodetector 402 is reset to the default voltage for the first pulse 308-1 of subsequent object pixels 306 (e.g., object pixel 306-21).

[0056] Figure 5 An example environment 500 in which the receiver 212 and the intensity readout module 214 of the lidar system 102 operate is shown. The environment 500 can be the same as or different from Figure 3-1 the environment 300. In the environment 500, objects 108-22, 108-33, and 108-44 (not shown) are located at different distances from the lidar system 102 and have different reflectivities.

[0057] The transmitter 210 emits transmit signals 302-22, 302-33, and 302-44 respectively for the object pixels 306-22, 306-33, and 306-44. For each of the object pixels 306-22, 306-33, and 306-44, the transmit signal 302 includes pulses 308-1, 308-2, 308-3, and 308-4. The energy of the first pulse 308-1 is lower than the energy of the other pulses 308-2 to 308-4. In the depicted example, the first pulse 308-1 of each transmit signal 302 has approximately half the energy of the other pulses 308-2 to 308-4. In other examples, the energy of each transmit signal 302 is more or less than half the energy of the other pulses 308-2 to 308-4.

[0058] At least a portion of the transmit signals 302-22, 302-33, and 302-44 are respectively reflected by the objects 108-22, 108-33, and 108-44. The reflected portions are received by the lidar system 102 as return signals 304-22, 304-33, and 304-44. The bias voltage 502 of the photodetector 402 is set to the default value for the first pulse 308-1 of each object pixel in the object pixels 306. As described with respect to Figure 4 as described, the photodetector 402 receives the return signal 304 and outputs the pulse data 410 of the first pulse 308-1. The intensity readout module 214 processes the pulse data 410 of the first pulse 308-1 of each return signal in the return signal 304. Based on the energy of the first pulse 308-1, the intensity readout module 214 or the controller of the receiver 212 outputs a bias control signal 414 to the receiver 212 to adjust the bias voltage 502 of the photodetector 402.

[0059] In the environment 500, the object 108-22 (not shown) is located near the lidar system 102 and / or has a high reflectivity. The controller can determine whether the peak or energy of the sampled pulse data 420-1 exceeds an upper threshold 510. The upper threshold 510 can be based on an amplitude level or an energy level. For example, the controller can determine whether the amplitude value of the sampled pulse data 420-1 of the first pulse 308-1 exceeds the upper threshold 510. In another example, the controller can determine whether the energy of the sampled pulse data 420-1 represented by the area under the sampled pulse data 420-1 exceeds the upper threshold 510. In the depicted example, the amplitude of the sampled pulse data 420-1 of the first pulse 308-1 is higher than the upper threshold 510.

[0060] Since the sampled pulse data 420-1 exceeds the upper threshold 510, the controller outputs a bias control signal 414 to the receiver 212. As a result, for other pulses 308-2 to 308-4 of the return signal 304-22, the bias voltage 502-22 of the photodetector 402 is reduced. The bias voltage 502-22 can be reduced to a set voltage or reduced by a set amount below the default bias voltage (e.g., about half of the default bias voltage). The reduction of the bias voltage 502-22 for other pulses 308-2 to 308-4 can be based on the ratio of the energy of the first pulse 308-1 to the energy of other pulses 308-2 to 308-4 in the transmitted signal 302. For example, if the energy of the first pulse 308-1 is one quarter of the energy of other pulses 308-2 to 308-4 in the transmitted signal 302, then in the case where the upper threshold 510 is exceeded, the bias voltage 502-22 for other pulses 308-2 to 308-4 can be reduced by twenty-five percent.

[0061] In other cases, the bias voltage 502-22 linearly decreases in proportion to the amount by which the amplitude or energy of the sampled pulse data 420-1 exceeds the upper threshold 510. For example, if the amplitude of the sampled pulse data 420-1 is thirty percent greater than the upper threshold 510, the bias voltage 502-22 is reduced by thirty percent. The upper threshold 510 can also include multiple thresholds and the bias voltage 502-22 can be adjusted according to which upper thresholds are exceeded.

[0062] In the depicted example, the bias voltage 502-22 of other pulses 308-2 to 308-4 in the object pixel 306-22 is reduced by about fifty percent. As a result, for pulses 308-2 to 308-4, the sensitivity of the photodetector 402 is reduced by about fifty percent. Although the energy of pulses 308-2 to 308-4 in the return signal 304-22 is greater, the energy of the sampled pulse data 420-2 to 420-4 of pulses 308-2 to 308-4 is respectively approximately the same as the energy of the sampled pulse data 420-1. Since the bias voltage 502-22 is reduced, the photodetector 402 receives and processes pulses 308-2 to 308-4 within its linear region.

[0063] The bias voltage 502 is adjusted to maintain the operation of the lidar system 102 within the linear region of the photodetector 402. To this end, the value of the upper threshold 510 is set based on the maximum incident energy capacity of the photodetector 402 and the ratio of the transmitted energy of the first pulse 308-1 to the transmitted energy of the other pulses 308-2 to 308-4. For example, if the incident energy is less than approximately seventy percent of its maximum incident energy capacity, the photodetector 402 operates in the linear region. Since the transmitted energy of the first pulse 308-1 is approximately half of the transmitted energy of the other pulses 308-2 to 308-4, the upper threshold 510 is approximately thirty-five percent of the maximum incident energy capacity of the photodetector 402.

[0064] In the environment 500, an object 108-33 (not shown) is located at a certain distance near the range center of the lidar system 102. The energy of the sampled pulse data 420-1 of the first pulse 308-1 of the return signal 304-33 is lower than the upper threshold 510 and higher than the lower threshold 512. As a result, for the other pulses 308-2 to 308-4 of the return signal 304-33 in the object pixel 306-33, the bias voltage 502-33 remains unchanged. The energies of the sampled pulse data 420-2 to 420-4 of the pulses 308-2 to 308-4 are approximately twice the energy of the sampled pulse data 420-1, but still within the linear region of the photodetector 402.

[0065] The object 108-44 (not shown) is far from the lidar system 102 and / or has a low reflectivity. The energy of the sampled pulse data 420-1 of the first pulse 308-1 of the return signal 304-44 is lower than the lower threshold 512. As a result, for the other pulses 308-2 to 308-4 of the return signal 304-44, the bias voltage 502-44 of the photodetector 402 is increased. The bias voltage 502-44 can be increased to a set voltage or increased by a set amount higher than the default bias voltage (e.g., approximately twice the default bias voltage). The increase in the bias voltage 502-44 for the other pulses 308-2 to 308-4 can be based on the ratio of the first pulse 308-1 to the transmitted energy of the other pulses 308-2 to 308-4. For example, if the energy of the first pulse 308-1 is one-fourth of the energy of the other pulses 308-2 to 308-4 in the transmitted signal 302, the bias voltage 502-44 for the other pulses 308-2 to 308-4 can be increased by twenty-five percent without exceeding the lower threshold 512.

[0066] In other cases, the bias voltage 502-44 linearly increases in proportion to the amount by which the amplitude or energy of the sampled pulse data 420-1 is below a lower threshold 512. For example, if the amplitude of the sampled pulse data 420-1 is thirty percent lower than the lower threshold 512, the bias voltage 502-44 increases by thirty percent. The lower threshold 512 may also include multiple thresholds and may adjust the bias voltage 502-22 based on which upper thresholds are not exceeded.

[0067] In the depicted example, the bias voltage 502-44 of the other pulses 308-2 to 308-4 in the object pixel 306-44 is increased by approximately fifty percent. As a result, for the pulses 308-2 to 308-4, the sensitivity of the photodetector 402 is increased by approximately fifty percent. The increase in the bias voltage 502-44 improves the ability of the photodetector 402 to detect the other pulses 308-2 to 308-4. The increased sensitivity may allow the lidar system 102 to distinguish the other pulses 308-2 to 308-4 from the internal noise of the lidar system 102, or improve the accuracy of the lidar data 416.

[0068] The value of the lower threshold 512 may be set based on the minimum incident energy capacity of the photodetector 402. The minimum incident energy capacity of the photodetector 402 is the minimum incident energy for generating accurate lidar data 416 for the lidar system 102. Below the minimum incident energy level, the lidar system 102 may not be able to confidently distinguish the pulses 308 from the internal noise. In the depicted example, the lower threshold 512 is set to the minimum incident energy capacity of the photodetector 402.

[0069] By adjusting the bias voltage 502 of the photodetector 402 for the subsequent pulses 308-2 to 308-N of the return signal 304 for each object pixel 306, the dynamic range of the lidar system 102 is increased. For example, the dynamic range of the lidar system 102 may be increased to at least ten times. The bias voltage adjustment allows the lidar system 102 to maintain accurate intensity measurements in short-range and / or high-reflectivity scenarios while increasing its sensitivity to the return signal 304 in long-range and / or low-reflectivity scenarios.

[0070] Example Method

[0071] Figure 6 An example method 600 for increasing the dynamic range of a ToF lidar system is depicted. The method 600 is shown as multiple sets of operations (or actions) to be performed, but is not necessarily limited to the order or combination of operations shown herein. Additionally, one or more of the operations may be repeated, combined, or reorganized to provide other methods. In the following discussion sections, reference may be made separately to Figure 1 andFigure 3-1 environments 100 and 300, and Figures 1 to 5 the entities detailed in, are referenced only as examples. The technology is not limited to being performed by one or more entities.

[0072] At 602, at least two pulses are emitted for an object pixel. A first pulse of the at least two pulses is emitted with less energy than the other pulses of the at least two pulses. For example, the transmitter 210 of the lidar system 102 on the vehicle 104 emits an emission signal 302-11 for the object pixel 306-11, as Figure 3-1 shown. The emission signal 302-11 includes a pulse train having at least two pulses 308 (e.g., pulses 308-1 to 308-4). The first pulse 308-1 has less energy than the other pulses 308-2, 308-3, and 308-4.

[0073] At 604, a first return pulse of the object pixel is received as a reflection of the first pulse. The first return pulse is received using a photodetector configured to sense the reflection of at least two pulses. For example, the photodetector 402 of the receiver 212 of the lidar system 102 receives a return signal 304-11 of the object pixel 306-11, as Figure 3-1 shown. The return signal 304-11 includes the first return pulse 308-1.

[0074] At 606, based on the amount of energy of the first return pulse, before receiving one or more other return pulses of the object pixel as reflections of the other pulses, the bias voltage of the photodetector is adjusted. For example, for the other pulses 308-2 to 308-4 of the object pixel 306-11, the bias voltage of the photodetector 402 of the receiver 212 is increased or decreased. The adjustment of the bias voltage is based on the amount of energy of the first return pulse 308-1 of the return signal 304-11, as described with respect to Figure 5 this.

[0075] At 608, at least two return pulses are output. For example, the intensity readout module 214 of the lidar system 102 outputs intensity data 412 associated with the pulses 308 of the return signal 304-11 to the processor 216 of the lidar system 102.

[0076] Examples

[0077] In the following sections, examples are provided.

[0078] Example 1: A transceiver of a lidar system, the transceiver being configured to: emit at least two pulses for an object pixel by: emitting a first pulse from the at least two pulses with less energy than the other pulses of the at least two pulses; receiving a first return pulse of the object pixel as a reflection of the first pulse using a photodetector configured to sense the reflection of the at least two pulses; adjusting a bias voltage of the photodetector based on an amount of energy of the first return pulse before receiving one or more other return pulses of the object pixel as reflections of the other pulses; and outputting at least two return pulses to a processor of the lidar system, the at least two return pulses including the first return pulse of the object pixel and one or more other return pulses of the object pixel.

[0079] Example 2: The transceiver of Example 1, wherein the transceiver is configured to adjust the bias voltage of the photodetector by: increasing the bias voltage of the photodetector when the energy of the first return pulse is less than a lower threshold; or, decreasing the bias voltage of the photodetector when the energy of the first return pulse is greater than an upper threshold.

[0080] Example 3: The transceiver of Example 2, wherein the lower threshold includes a minimum incident energy capacity of the photodetector and the upper threshold includes less than a maximum incident energy capacity of the photodetector.

[0081] Example 4: The transceiver of Example 2, wherein the bias voltage is increased or decreased by a set amount, the set amount including half of the bias voltage of the photodetector before receiving one or more other return pulses of the object pixel.

[0082] Example 5: The transceiver of Example 2, wherein the transceiver is further configured to adjust the bias voltage of the photodetector by: in increasing the bias voltage of the photodetector, increasing the bias voltage by a first amount based on a ratio of the energy of the first return pulse to the upper threshold; and in decreasing the bias voltage of the photodetector, decreasing the bias voltage by a second amount based on a ratio of the energy of the first return pulse to the lower threshold.

[0083] Example 6: The transceiver of Example 1, wherein the transceiver is further configured to: adjust the bias voltage of the photodetector by adjusting the bias voltage of the photodetector in proportion to a ratio between the energy of the first return pulse and a threshold.

[0084] Example 7: The transceiver of Example 6, wherein the threshold includes less than half of the maximum incident energy capacity of the photodetector.

[0085] Example 8: The transceiver of Example 1, further configured to: output a return pulse as a combined return signal of the object pixel.

[0086] Example 9: The transceiver of Example 1, wherein the photodetector comprises a silicon photomultiplier, an avalanche photodiode, a single photon avalanche diode, a photomultiplier tube, or a PIN diode.

[0087] Example 10: The transceiver of Example 1, wherein at least two pulses for an object pixel comprise at least four pulses for the object pixel.

[0088] Example 11: The transceiver of Example 1, wherein the amount of energy of the first pulse is approximately half the amount of energy of each of the other pulses.

[0089] Example 12: A method comprising: emitting, by a transceiver of a lidar system, at least two pulses for an object pixel by: emitting a first pulse from the at least two pulses with less energy than the other pulses of the at least two pulses; receiving, using a photodetector of the transceiver, a first return pulse of the object pixel as a reflection of the first pulse; adjusting, based on the amount of energy of the first return pulse, a bias voltage of the photodetector before receiving one or more other return pulses of the object pixel as reflections of the other pulses; and outputting to a processor of the lidar system at least two return pulses, the at least two return pulses comprising the first return pulse of the object pixel and one or more other return pulses of the object pixel.

[0090] Example 13: The method of Example 12, wherein adjusting the bias voltage of the photodetector before receiving one or more other return pulses of the object pixel as reflections of the other pulses comprises: increasing the bias voltage of the photodetector when the energy of the first return pulse is less than a lower threshold; or decreasing the bias voltage of the photodetector when the energy of the first return pulse is greater than an upper threshold.

[0091] Example 14: The method of Example 13, wherein the lower threshold comprises a minimum incident energy capacity of the photodetector and the upper threshold comprises less than a maximum incident energy capacity of the photodetector.

[0092] Example 15: The method of Example 13, wherein the bias voltage is increased or decreased by a set amount, the set amount comprising half of the bias voltage of the photodetector before receiving one or more other return pulses of the object pixel.

[0093] Example 16: The method of Example 13, further comprising: in increasing the bias voltage of the photodetector, increasing the bias voltage by a first amount, the first amount being based on a ratio of the energy of the first return pulse to the lower threshold; and in decreasing the bias voltage of the photodetector, decreasing the bias voltage by a second amount, the second amount being based on a ratio of the energy of the first return pulse to the upper threshold.

[0094] Example 17: The method of Example 12, wherein adjusting the bias voltage of the photodetector before receiving one or more other return pulses of the object pixel includes: adjusting the bias voltage of the photodetector in proportion to the ratio between the energy of the first return pulse and a threshold, the threshold including less than half of the maximum incident energy capacity of the photodetector.

[0095] Example 18: The method of Example 12, further comprising: outputting the return pulse as a combined return signal of the object pixel.

[0096] Example 19: The method of Example 12, wherein at least two pulses for the object pixel include at least four pulses for the object pixel.

[0097] Example 20: A lidar system, comprising: means for emitting at least two pulses for an object pixel by: emitting a first pulse from the at least two pulses with less energy than other pulses of the at least two pulses; means for receiving a first return pulse of the object pixel as a reflection of the first pulse; means for adjusting the bias voltage of the means for receiving before receiving one or more other return pulses of the object pixel as reflections of the other pulses based on the amount of energy of the first return pulse; and means for outputting at least two return pulses including the first return pulse of the object pixel and one or more other return pulses of the object pixel.

[0098] Conclusion

[0099] Although various embodiments of the present disclosure have been described in the foregoing description and illustrated in the accompanying drawings, it should be understood that the present disclosure is not limited thereto, but may be implemented in various ways within the scope of the following claims for practice. From the foregoing description, it will be apparent that various changes may be made without departing from the spirit and scope of the present disclosure as defined by the following claims.

Claims

1. A method for a lidar system, comprising: transmitting, by a transceiver of the lidar system, a transmission signal including at least two pulses for one object pixel among a plurality of object pixels by: transmitting a first pulse from the at least two pulses with less energy than other pulses of the at least two pulses of the transmission signal, the plurality of object pixels including a field of view of the lidar system; receiving, by a photodetector of the transceiver, a first return pulse of a return signal of the object pixel as a reflection of the first pulse of the transmission signal, the return signal being a reflection of the transmission signal; adjusting, by an intensity readout module and based on an amount of energy of the first return pulse of the return signal, a bias voltage of the photodetector before receiving one or more other return pulses of the return signal of the object pixel as reflections of the other pulses of the at least two pulses of the transmission signal; resetting, by the intensity readout module, the bias voltage of the photodetector to a default voltage for receiving a first return pulse of a subsequent object pixel among the plurality of object pixels; and outputting, by the intensity readout module, intensity data of the return signal generated by the intensity readout module to a processor of the lidar system, the intensity data indicating the amount of energy of the first return pulse of the object pixel and the amount of energy of the one or more other return pulses of the object pixel.

2. The method according to claim 1, wherein Adjusting the bias voltage of the photodetector before receiving one or more other return pulses of the object pixel includes: increasing the bias voltage of the photodetector when the amount of energy of the first return pulse is less than a lower threshold; or decreasing the bias voltage of the photodetector when the amount of energy of the first return pulse is greater than an upper threshold.

3. The method according to claim 2, wherein The lower threshold includes a minimum incident energy capacity of the photodetector, and the upper threshold includes less than a maximum incident energy capacity of the photodetector.

4. The method according to claim 2, characterized in that The bias voltage is increased or decreased by a set amount, the set amount including half of the bias voltage of the photodetector before receiving one or more other return pulses of the object pixel.

5. The method according to claim 2, characterized in that, Further comprising: in increasing the bias voltage of the photodetector, increasing the bias voltage by a first amount, the first amount being based on a ratio of the amount of energy of the first return pulse to the lower threshold; and in decreasing the bias voltage of the photodetector, decreasing the bias voltage by a second amount, the second amount being based on a ratio of the amount of energy of the first return pulse to the upper threshold.

6. The method according to any one of claims 1 to 5, characterized in that, Adjusting the bias voltage of the photodetector before receiving one or more other return pulses of the object pixel includes: adjusting the bias voltage of the photodetector in proportion to a ratio between the amount of energy of the first return pulse and a threshold.

7. The method according to claim 6, characterized in that, The threshold includes less than half of the maximum incident energy capacity of the photodetector.

8. The method according to any one of claims 1 to 5, characterized in that Outputting the intensity data of the return signal includes collecting the intensity data of the first return pulse and the one or more other return pulses into a combined signal and sending the combined signal to the processor.

9. The method according to any one of claims 1 to 5, characterized in that, The at least two pulses for the object pixel include at least four pulses for the object pixel.

10. The method according to any one of claims 1 to 5, characterized in that, The amount of energy of the first pulse is half the amount of energy of each of the other pulses.

11. A lidar system, comprising: a transceiver, an intensity readout module, and a processor configured to perform the method according to any one of claims 1 to 10.

12. The lidar system according to claim 11, wherein, The photodetector includes a silicon photomultiplier, an avalanche photodiode, a single photon avalanche diode, a photomultiplier tube, or a PIN diode.

13. The lidar system according to claim 11, wherein, The lidar system is integrated within a vehicle or mounted to a vehicle.

14. The lidar system according to claim 11, wherein, Adjusting the bias voltage of the photodetector increases the dynamic range of the lidar system, where the dynamic range represents the ability of the lidar system to accurately process return signals reflected from an object at a short distance relative to a long distance or at a high reflectivity relative to a low reflectivity.

15. The lidar system according to claim 11, wherein: The intensity readout module determines the amount of energy of the first return pulse.

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