A Fully Integrated Doppler-Assisted FMCW Radar With Low Hertz-Range Noise Figure and High Chirp Linearity for Vital Signs Sensing and Indoor Localization

This article presents a Doppler-assisted frequency-modulated continuous-wave (FMCW) radar that combines precise range resolution capability of FMCW with high sensitivity of Doppler radar, enabling versatile performance for indoor applications. A comprehensive analysis of low-frequency noise contributions from key receiver (RX) blocks including low-noise amplifier (LNA), mixer, local oscillator (LO) buffer, and analog baseband (ABB) circuits is conducted. An “RF+LO+BB” joint noise figure (NF) improvement method is proposed to effectively suppress the low-frequency noise. To minimize frequency modulation (FM) error in charge-pump-based fractional-N phase-locked loops (PLLs), a nested-PLL architecture with an optimized loop parameter selection method is employed, significantly enhancing chirp linearity. Fabricated in a 55-nm CMOS technology, the proposed Doppler-assisted FMCW radar achieves NFs of 32.13 and 12.94 dB at 10 Hz and 1 kHz, respectively, and a chirp linearity of 0.0039% over a 3.52 GHz chirp bandwidth (BW), resulting in a maximum detection range of 19.41 m and a range resolution of 4.7 cm. The radar occupies a die area of 12.7 mm² and consumes 594 mW in FMCW mode and 432 mW in Doppler mode under a 3.3 V supply.