Phase Locked Loop with Ramp Generator for FMCW LiDAR TX in 28-nm CMOS

Frequency-Modulated Continuous Wave Light Detection and Ranging (FMCW LiDAR) is a coherent detection system that can achieve high resolution even with a low clock frequency. The frequency of the laser must be modulated with a constant slope over time. For this purpose, we study the design of a circuit for inputting a ramp wave to a laser and a PLL to compensate for the nonlinearity of the laser. The CMOS chip, which outputs an 8kV/s slope ramp wave, consists of a phase-frequency detector, charge pump, loop filter, ramp generator, etc. Through negative feedback, the beating frequency is kept equal to the reference frequency. As a result of post-simulation, the modulation slope error was confirmed to be less than 0.1%, and the Electric-Optical PLL system will be able to have a higher Signal-to-Noise Ratio and resolution than an open loop system.