A High-Resolution FPGA-Based Time-to-Amplitude Converter (TAC) with Integrated Pulse-Width-Based Walk Error Compensation: Design and Experimental LiDAR Validation

LiDAR is a key sensor for depth perception in applications ranging from autonomous vehicles and industrial robotics to robotic vacuum cleaners and topographic mapping, with its depth resolution determined by the timing electronics. This article, to the best of our knowledge, presents the first implementation of an FPGA-based time-to-amplitude converter (TAC) in a LiDAR system alongside the first integration of walk error compensation into such an architecture. The threshold-crossing time shifts with the echo amplitude, causing walk error. This walk error can reach tens of centimeters depending on target reflectivity and range. Pulse-width-based correction has been demonstrated, but reported implementations obtain the time-of-flight (ToF) and the pulse width with time-to-digital converters (TDCs), whose high resolution relies on high-speed clocks for coarse time and delay lines for fine-time measurements, which suffer from coarse-count ambiguity, bin calibration requirements, sensitivity to process, voltage, and temperature (PVT) variations, and portability limitations. This article enhances the novel FPGA-based TAC previously introduced by the authors for pulse-width-based walk error compensation without using a clock or a delay line. Each ToF channel requires only one D flip-flop in the FPGA and a low-cost external passive circuit coupled to the multichannel analog-to-digital converter (ADC) of the FPGA. Using our FPGA-based TAC in our LiDAR experimental setup, the walk-induced distance error is successfully reduced from 42 cm to 2 cm, and target distances of up to 3 m are measured within a 2 cm maximum error.