Fast-Locking Electro-Optic PLL with Harmonic Suppression and Lock-in Calibration for FMCW LiDAR

An Electro-Optic Phase-Locked Loop (EOPLL) is introduced for application in Frequency Modulated Continuous Wave (FMCW) Light Detection And Ranging (LiDAR), aimed at mitigating the impact of laser nonlinearity, temperature variations, and voltage fluctuations. Nonlinearity in the laser can significantly affect the detection accuracy of LiDAR. The proposed EOPLL substantially improves the linearity of the laser from 90% to 99.9% within a temperature range of 10-60 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula>C. The proposed EOPLL exhibits an advantage over wideband PLLs by incorporating Harmonic Suppression (HS) mixing technology into the loop and providing harmonic suppression capabilities, which effectively overcomes challenging spurious issues. Additionally, a bleed current phase adjustment technique has been introduced to align the phase input-to-clock for lower harmonics. Consequently, a significant 29dB enhancement in suppressing the third harmonic of the beat signal is attained. The bandwidth of FMCW LiDAR is critical because the extend of the lock time affects the effective detection bandwidth. In response to relocking issues associated with EOPLLs, a switchable Lock-in calibration technique is proposed to reduce the locking time and increase the effective bandwidth from 50% to 90%.