A Self-Calibrated 16-GHz Subsampling-PLL-Based Fast-Chirp FMCW Modulator With 1.5-GHz Bandwidth

This article presents a 16-GHz frequency-modulated continuous-waveform (FMCW) modulator for radar applications in 28-nm CMOS. A two-point modulation technique is applied to reach a fast-chirp operation. A digital-to-time converter (DTC)-based subsampling phase-locked loop (PLL) is implemented to eliminate the power and noise from the frequency divider. Compared with the conventional delta-sigma division ratio-modulated PLL, this article presents an FM modulator with a finer loop-time resolution that lowers the quantization noise and improves the chirp FM accuracy. A voltage-driven analog varactor enables a programmable chirp bandwidth up to 1.5 GHz. The frequency-digital to analog converter (FDAC) nonlinearity is pre-distorted by an on-chip calibration engine. This FMCW modulator chirps 1.5-GHz bandwidth within 10 μs. The corresponding root-mean-square (rms) frequency error is 230 kHz, which is less than 0.015% of the chirp bandwidth.