An analog front-end (AFE) circuit comprising an amplifier module, a peak detector, and a timing discriminator has been designed to facilitate the target identification for direct time-of-flight (dToF) LiDAR. The amplitude saturation error (ASE) is compensated in this article for the intensity determination, which is conducted based on the combination of the pulse width and peak detector. Together with the improved walk error compensation scheme, the proposed AFE circuit can attain the distance and intensity information simultaneously with lower cost and larger dynamic range. A specific frequency compensation method is proposed with a shunt feedback TIA, which improves the stability and mitigates the impact of the package parasitics. The measured -3-dB bandwidth, transimpedance gain, and the input-referred noise current are 281 MHz, 86 dB $\Omega $ , and 4.68 pA/ $\surd $ Hz respectively. The proposed AFE circuit, which is fabricated in $0.18~\mu \text{m}$ CMOS technology, achieves the distance accuracy of ±30 ps and the intensity accuracy of ±4% in the dynamic range of 1:5000 without gain control scheme.

A Low Walk Error Analog Front-End Circuit With Intensity Compensation for Direct ToF LiDAR

This article presents an 8-ch LIDAR receiver for pulsed time-of-flight (TOF) imaging laser detection and ranging application. The proposed LIDAR receiver can achieve both 100 m and high-precision range imaging with lower system cost, which was untrodden with conventional LIDARs. The time-to-digital converter (TDC) with multi-intervals detection is used to measure the TOF and eliminate the walking error. Spatial Savitzky–Golay smoothing filter (SSGSF) is used to improve measuring range and precision of the LIDAR system, which is based on mixed timing sampling (MTS). The MTS is realized by TDC, analog-to-digital converter (ADC) with 200-MS/s sampling rate, and mixed interpolation algorithm. Based on the proposed LIDAR receiver, extensive experiments have been performed to verify the performance of the LIDAR receiver. The ranging precision of the LIDAR receiver is 40 mm when the rising time of the echo signal is 3 ns and the signal-to-noise ratio (SNR) is 10. Furthermore, the LIDAR receiver achieves a measurement range of 100 m with a peak power of 30 W and an execution time of $2.4~\mu \text{s}$ for a complete measurement.

An 8-ch LIDAR Receiver Based on TDC With Multi-Interval Detection and Real-Time $In~Situ$ Calibration

Airborne LiDAR: state-of-the-art of system design, technology and application

Positioning and perception in LIDAR point clouds

A misalignment of LiDAR as low as a few degrees could cause a significant error in obstacle detection and mapping that could cause safety and quality issues. In this paper, an accurate inspection system is proposed for estimating an automotive LiDAR alignment error after sensor attachment on a vehicle. The proposed method uses only a single target board at a close range to estimate the orientations and the horizontal position of the LiDAR attachment with sub-degree and millimeter level accuracy. It is a static method for the stationary target board and vehicle during the inspection. Also, it only requires one pose of the target board and does not utilize other sensors, such as a camera or GPS. The performance of the proposed method is evaluated using a test bench that can control the reference yaw and horizontal translation of LiDAR within ranges of 3 degrees and 30 millimeters, respectively. The experimental results for a low-resolution 16 channel LiDAR (Velodyne VLP-16) confirmed that misalignment could be estimated with accuracy within 0.2 degrees and 4 mm. The high accuracy and simplicity of the proposed system make it practical for large-scale industrial applications such as automobile manufacturing process that inspects the sensor attachment for the safety quality control.

Accurate Alignment Inspection System for Low-Resolution Automotive LiDAR

In this paper, an online echo waveform fitting-based method is proposed for the real-time in situ laser ranging. In the method, an embedded FPGA is employed to realize the fast single-pulse fitting, and the parameters of the echo waveform of an object under detection are, thus, extracted in an online manner. The parameters of the echo waveform are utilized to estimate the time interval between the emitted pulse and the echo. The distance of the object is then calculated from the time interval. The simulations were first done to analyze and obtain the computational resource consumption and the time cost of a single measurement. Then, an FPGA- and ADC-based ranging system was designed, and an experiment was carried out to verify the proposed method. The results show that a single measurement of the distance can be done within $8.7~\mu \text{s}$ , which is fast enough for online ranging. At a distance of 70 m with an SNR of 18.4 dB, the mean range error and the range standard deviation are 4.9 and 10.7 cm, respectively. In addition, the proposed method was also compared with the TDC-based in situ method and the Gauss–Newton algorithm-based off-line method.

Real-Time In Situ Laser Ranging Based on Online Echo Waveform Fitting

To achieve online multi-target laser ranging in full-waveform light detection and ranging (LiDAR), a multi-target laser ranging method using waveform decomposition is proposed and implemented on a field programmable gate array (FPGA). In this method, an emitted laser pulse and the laser echo scattered from multiple targets are decomposed into a set of Gaussian functions, then the distances between the LiDAR and the targets are obtained using the waveform parameters of Gaussian functions. The waveform decomposition method is modified and implemented on a FPGA for online laser ranging. Simulations and experiments were conducted to verify the ranging performances of the proposed method by the comparition with those of a post-processing Gauss-Newton (post-GN) method. The results of simulations show that the proposed method is more efficient compared with the post-GN method. The time cost reduces 79.8% to 91.1% for a laser echo scattered from three close targets. In experiments, a lab-built full-waveform LiDAR system was used to obtain the waveforms of emitted laser pulses and laser echoes scattered from 1, 2, or 3 targets. The results show that the ranging performances of the proposed method are comparable with those of the post-GN method. The proposed method is capable to distinguish close targets with an equivalent time space of 1.8 times pulse width of an emitted laser pulse and decompose laser echo with a signal-to-noise ratio (SNR) higher than 20 dB. The results show that the proposed method can obtain distances of multiple close targets from a laser echo efficiently and accurately.

Zining Wang

Papers

Airborne LiDAR: state-of-the-art of system design, technology and application

Real-Time In Situ Laser Ranging Based on Online Echo Waveform Fitting

Online Multi-Target Laser Ranging Using Waveform Decomposition on FPGA