Abstract
Light detection and ranging (LiDAR) systems sense the distance by illuminating a target and detecting the reflected optical signal. Depending on the modulation method, LiDAR systems can be categorized into three types: pulse time-of-flight (ToF) [1], [2], phase-shift (PS) [3], and frequency-modulated continuous-wave (FMCW), where the pulse and PS are more widely used than FMCW. Fig. 1 illustrates the principle of ToF and PS methods. The accuracy of ToF measurements, as shown in equation (1) of Fig. 1, depends on the precision of the flight time measurement, which typically requires a picosecond-level time-to-digital converter (TDC) for high precision ranging of millimeter level. As for PS ranging, the carrier frequency limits the maximum detectable ambiguity, which is known as 2π limitation as indicated by equation (2). Although multi-frequency ranging can be used to achieve high precision and extend the measurement scope [4], it increases the design complexity of the ranging system. A hybrid pulse-phase ranging system based on an under-sampling technique is proposed in [5]. However, the maximum detectable range is limited by the carrier frequency, resulting in slow phase discrimination compared to prior work.