Various embodiments of the present disclosure are generally directed to an apparatus and method for adaptively adjusting amplifier gain based on detected distance to a target in a light detection and ranging (LiDAR) system.
Without limitation, in some embodiments the amplifier amplifies detected pulses obtained from a photodetector, and a gain applied to the amplifier output is adjusted from among at least two selectable gain modes responsive to a measured time of flight (ToF) for the pulses. A first range of gain levels can be used for targets that are within a first maximum distance range, and a second range of gain levels can be used for targets that are beyond the first maximum distance range. Each mode can extend from a minimum to a maximum value along a selected linear slope. A gain adjustment circuit can use a Gilbert Cell or a multiplier and fully differential amplifier arrangement.
These and other features and advantages of various embodiments can be understood from a review of the following detailed description section in conjunction with a review of the accompanying drawings.
Various embodiments of the present disclosure are generally directed to optimization of an active light detection system.
Light Detection and Ranging (LiDAR) systems are useful in a number of applications in which range information (e.g., distances, etc.) from an emitter to a target are detected by irradiating the target with electromagnetic radiation in the form of light. The range information is detected in relation to timing and/or waveform characteristics of reflected light received back by the system. LiDAR applications include autonomously piloted or driver assisted vehicle guidance systems, topographical mapping, surveying, and so on. LiDAR systems are particularly useful in generating a three-dimensional (3D) point cloud representation of the surrounding environment in the applicable field of view (FoV). While not limiting, the light wavelengths used in a typical LiDAR system may range from ultraviolet to near infrared (e.g., 250 nanometers, nm to 1500 nm or more) with native light frequencies in the terahertz (THz, 1012 Hz) range. Other wavelength and frequency ranges can be used.
One commonly employed form of LiDAR is sometimes referred to as coherent pulsed LiDAR, which generally uses coherent light and detects the range based on detecting phase differences in the reflected light. Such systems may use a dual (IQ) channel detector with an I (in-phase) channel and a Q (quadrature) channel. Other forms of LiDAR systems can be used, however, including non-coherent light systems that may incorporate one or more detection channels.
While operable, these and other systems can encounter difficulties in detecting targets at relatively longer distances, due to the time of flight of the various emitted pulses being relatively large. Various embodiments of the present disclosure compensate for these and other effects by using time-based feedback to adaptively adjust a gain associated with the generation and emission of the emitted beam for various targets within the FoV.
In some embodiments, an adaptive gain adjustment circuit is used to control feedback to an amplifier stage, which may take the form of a TIA (transimpedance amplifier). This allows dynamic control of the gain of a TIA without introducing artifacts at the detector, which may take the form of an avalanche photodetector (APD) or other detector device. In some cases, a Gilbert Cell arrangement is used to provide the different gain ranges. In other cases, a multipler arrangement along with a fully differential amplifier arrangement is used.
Different ranges of gain can be provided for different target distances. The gain differential in each range can vary, with a ratio of around 100:1 being used in some cases. In at least some embodiments, the gain of the amplifier is nominally maintained in a linear range.
These and other features and advantages of various embodiments can be understood beginning with a review of
The LiDAR system 100 includes a controller 104 which provides top level control of the system. The controller 104 can take any number of desired configurations, including hardware and/or software. In some cases, the controller can include the use of one or more programmable processors with associated programming (e.g., software, firmware) stored in a local memory which provides instructions that are executed by the programmable processor(s) during operation. Other forms of controllers can be used, including hardware based controllers, digital signal processors (DSPs), field programmable gate arrays (FPGAs), system on chip (SOC) integrated circuits, application specific integrated circuits (ASICs), gate logic, reduced instruction set computers (RISCs), etc.
An energy source circuit 106, also sometimes referred to as an emitter or a transmitter, operates to direct electromagnetic radiation in the form of light pulses toward the target 102. A detector circuit 108, also sometimes referred to as a receiver or a sensor, senses reflected light pulses received back from the target 102. The controller 104 directs operation of the emitted light from the emitter 106, denoted by arrow 110, and decodes information from the reflected light obtained back from the target, as denoted by arrow 112.
Arrow 114 depicts the actual, true range information associated with the intervening distance (or other range parameter) between the LiDAR system 100 and the target 102. Depending on the configuration of the system, the range information can include the relative or absolute speed, velocity, acceleration, distance, size, location, reflectivity, color, surface features and/or other characteristics of the target 102 with respect to the system 100.
The decoded range information can be used to carry out any number of useful operations, such as controlling a motion, input or response of an autonomous vehicle, generating a topographical map, recording data into a data structure for further analysis and/or operations, etc. The controller 104 perform these operations directly, or can communicate the range information to an external system 116 for further processing and/or use.
In some cases, inputs supplied by the external system 116 can activate and configure the system to capture particular range information, which is then returned to the external system 116 by the controller 104. The external system can take any number of suitable forms, and may include a system controller (such as CPU 118), local memory 120, etc. The external system may form a portion of a closed-loop control system and the range information output by the LiDAR system 100 can be used by the external system 116 to adjust the position of a moveable element.
The controller 104 can incorporate one or more programmable processors (CPU) 122 that execute program instructions in the form of software/firmware stored in a local memory 124, and which communicate with the external controller 118. External sensors 126 can provide further inputs used by the external system 116 and/or the LiDAR system 100.
that emits electromagnetic radiation (e.g. light) in a desired spectrum. The emitted light is processed by an output system 208 to issue a beam of emitted light 210. The light may be in the form of pulses, coherent light, non-coherent light, swept light, etc.
Regardless the configuration of the output system,
A low pass filter (LPF) 406 and an analog to digital converter (ADC) 408 can be used as desired to provide processing of the input pulses. A processing circuit 410 provides suitable signal processing operations to generate a useful output 412.
The response 602 may be applied to longer distance targets and the response 604 may be applied to closer targets. In other embodiments, the differential among targets within a given FoV may be evaluated and a suitable gain range (e.g., 602, 604) may be selected that optimally accounts for the various targets with appropriate weighting. In still other embodiments, different gains may be instantaneously supplied for different targets within the same FoV based on their different detected distances.
This arrangement allows the use of an adaptive gain adjustment circuit that adjusts a gain of an amplifier used to detect pulses reflected from a target to provide at least two selectable gain modes, each of the gain modes associated with a different measured time of flight of a light beam emitted by the system to the target. A range detection circuit can be used to determine a distance between the LiDAR system and the target, and the adaptive gain adjustment circuit can operate to change the gain of the amplifier from a first range of gain levels to a different second range of gain levels responsive to the determined distance (e.g., switch between profile 602 and 604, etc.). In some cases, the first range of gain levels can be used for targets that are within a first maximum distance range, and the second range of gain levels can be used for targets that are beyond the first maximum distance range.
A pulse detect stage 702 receives reflected pulses from a selected target. As described above, this can include optics, APDs, and other front-end processing elements. The output is supplied to a TIA 704 which converts the input current pulse to a voltage pulse of selected magnitude. The TIA 704 may further act as an electronic filter, such a low-pass filter that removes or attenuates high-frequency electrical noise by attenuating signals above a particular frequency.
The TIA 704 may be provided with its own internal adjustable gain stage, or a separate downstream gain stage (not shown) can be provided to amplify the output voltage signal to a selected range as set forth above in
A time/distance determination circuit 708 receives the edge detection signals from the comparator 706 and determines range information therefrom, including an interval of time between emission of a pulse of light by the light source of the emitter (see
The ToF flight information is used to generate an accurate determination of the actual distance between the emitter and the target. This information is supplied to a gain adjustment circuit 710, which in turn adjusts a gain utilized of the TIA 704. Longer distance targets will tend to provide lower power reflected signals and hence, may be processed using a higher (greater slope) gain range (e.g., 602), while shorter distance targets will provide higher power reflected signals and hence may be processed using a lower (flatter slope) gain range (e.g., 604). It can be seen that the various gain ranges supplied by the gain range adjustment circuit 710 can be both over absolute gain range values as well as differences between the minimum and maximum values within the range. This provides the system with the capability of providing an optimum resolution of the point cloud data based on the actual range to the target.
A LiDAR system such as 100 in
Light pulses are transmitted at block 1006 to illuminate various targets within the FoV as described above including the emitter 200 of
As described previously, different gain ranges can be selected and used for different targets within the same FoV. Closer targets within the point cloud can be provided with one range with a lower slope and magnitude values to obtain optimal resolution of the closer targets, while at the same time farther targets within the point cloud can be provided with one or more different gain ranges with higher slopes and/or different magnitude values to obtain optimal resolution of the farther targets.
Reflected from the target is a received set of pulses 1112 including pulses 1114 (pulse P1) and 1116 (pulse P2). The time of flight (TOF) value for pulse P1 is denoted at 1118. Similar TOF values are provided for each pulse in turn.
The received P1 pulse 1114 will likely undergo frequency doppler shifting and other distortions as compared to the emitted P1 pulse 1104. The same is generally true for each successive sets of transmitted and received pulses such as the P2 pulses 1106, 1116. Nevertheless, the frequencies, phase and amplitudes of the received pulses 1114, 1116 will be processed as described above to enable the detector circuit to correctly match the respective pulses and obtain accurate distance and other range information.
The manager circuit 1202 uses a number of inputs including system configuration information, measured distance for various targets, various other sensed parameters from the system (including external sensors 126), history data accumulated during prior operation, and user selectable inputs. Other inputs can be used as desired.
The manager circuit 1202 uses these and other inputs to provide various outputs including accumulated history data 1204 and various profiles 1206, both of which can be stored in local memory such as 124 for future reference. The history data 1204 can be arranged as a data structure providing relevant history and system configuration information. The profiles 1206 can describe different pulse set configurations with different numbers of pulses at various frequencies and other configuration settings, as well as other appropriate gain levels, ranges and slopes for different sizes, types, distances and velocities of detected targets.
The manager circuit 1202 further operates to direct various control information to an emitter (transmitter Tx) 1208 and a detector (receiver Rx) 1210 to implement these respective profiles. It will be understood that the Tx and Rx 1208, 1210 correspond to the various emitters and detectors described above.
From the foregoing description it can be seen that the adaptive gain adjustments can be implemented in a number of ways, such as through the use of a fully differential amplifier and a Gilbert cell, or a multiplier and operational amplifier combination. Other circuit configurations can be used. While not necessarily required, the circuits advantageously maintain the transimpedance amp (TIA) in nominally a linear range. The differences in gain between min and max can be any suitable ratio, including up to or exceeding 100:1. In this way, one gain profile can be used for closer targets (e.g., lower time of flight) and the other gain profile can be used for farther targets (e.g., higher time of flight). Additional profiles can be selected based on substantially any desired operational parameters.
While coherent, I/Q based systems have been contemplated as a basic environment in which various embodiments can be practiced, such are not necessarily required. Rather, any number of different types of systems can be employed, including solid state, mechanical, etc.
It is to be understood that even though numerous characteristics and advantages of various embodiments of the present disclosure have been set forth in the foregoing description, together with details of the structure and function of various embodiments of the disclosure, this detailed description is illustrative only, and changes may be made in detail, especially in matters of structure and arrangements of parts within the principles of the present disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
The present application makes a claim of domestic priority under 35 U.S.C. 119(e) to U.S. Provisional Patent Application No. 63/220,726 filed Jul. 12, 2021, the contents of which are hereby incorporated by reference.
Number | Date | Country | |
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63220726 | Jul 2021 | US |