A Novel Time-to-Amplitude Converter and a Low-Cost Wide Dynamic Range FPGA TDC for LiDAR Application

Abstract

This paper demonstrates a low-cost wide dynamic range FPGA time-to-digital converter (TDC) and a time-to-amplitude converter (TAC) based on an embedded XOR gate of the FPGA and a low-complexity circuitry. TACs and TDCs are important for distance measurements in LiDAR systems in a wide range of applications from self-driving cars to topographic mapping. LiDAR’s high cost, relatively large size and complexity are important implementation challenges that need to be addressed. In the literature, external circuits are used to provide low phase noise clock signals into the FPGA TDC to measure long range time intervals adding to the complexity and cost. Our TDC can measure a wide dynamic range of 1 ms with high precision using a low-cost FPGA board. Calibration using dynamic phase-shifting (DPS) is conducted with a resolution of 18 ps. The performance measurements gave us insight on the relative temperature insensitive regions for operating the TDC. The ideal range was found to be 24°C to 39°C. We also present a novel TAC design to demonstrate that one XOR gate of a low-cost Artix-7 FPGA and a simple low-cost circuitry can detect a phase difference as low as 18 ps. The TAC’s linearity is presented through INL and DNL test results. For every additional channel, our TAC requires only one XOR gate in the FPGA chip and a low complexity circuitry. This allows for multichannel operation and larger area availability for use in other implementations. Performance measurements show our TAC to be highly insensitive to temperature and voltage changes.