A Highly Accurate and Sensitive mmWave Displacement-Sensing Doppler Radar With a Quadrature-Less Edge-Driven Phase Demodulator

A 110-mW 39-GHz Doppler radar front end in 65-nm CMOS for displacement and vibration sensing is proposed. Conventional Doppler radar suffers from detection nulls, at which the receiver detection gain drops to zero. Quadrature demodulation for either carrier frequency or intermediate frequency (IF) is necessary to alleviate nulls but still induces nonlinear detection gain that needs to be compensated through digital signal processing (DSP). In this article, a Doppler radar topology is proposed to achieve ultrahigh displacement range accuracy and sensitivity and to eliminate detection nulls without using quadrature demodulation. An edge-driven phase demodulator (EDPD) processes the rectified square-wave intermediate signal and converts displacement/vibration to a true-dc/baseband signal with a constant gain. Coherent demodulation and signal generation through common-referenced subsampling phase-locked loops (SSPLLs) allow the radar to achieve 4- $\mu \text{m}$ static range accuracy and 39-nm vibrational (at 10 kHz) range sensitivity in measurement.