A Fully-integrated Doppler-assisted FMCW Radar with Low Hertz Range Noise Figure for Indoor Localization and Vital Sign Sensing

This paper presents a Doppler-assisted frequency modulated continuous wave (FMCW) radar that leverages the benefits of FMCW’s range resolution and Doppler’s sensitivity for indoor applications. The Doppler mode reuses circuit blocks in the FMCW mode to reduce power consumption and area overhead. Low-frequency noise contributions from the receiver circuits are analyzed and an “$\mathbf{R F}+\mathbf{L O}+\mathbf{B B}$” combined noise figure (NF) optimization scheme is proposed to minimize the low-frequency noise. The radar employs a nested phase-locked loop frequency synthesizer with low phase noise and incorporates an optimized $\Delta T_{\text {step }}$ selection technique to improve chirp linearity. Designed in a 55-nm CMOS technology, the radar achieves NFs of 32 dB and 12 dB at 10 Hz and 1 kHz, respectively, and a chirp linearity of 0.0039% over a 3.52 GHz chirp bandwidth (BW), leading to a range resolution of 4.7 cm. The radar occupies an area of $12.7 \mathrm{mm}^{2}$, and consumes 220 mA of current in the FMCW mode and 160 mA in the Doppler mode under a power supply of 3.3 V.