This brief describes a phase-domain oversampled ranging method for high-resolution low-cost frequency-modulated continuous-wave (FMCW) radar systems, aiming for human health monitoring applications. To overcome the limited bandwidth problem for fine ranging resolution in the conventional FMCW radar systems, a ΔΣ ranging digital-intensive receiver architecture is proposed to achieve both wide capture range and fine resolution by utilizing a digital phase rotator and a 1-bit ΔΣ time-to-digital converter. A prototype 4-GHz FMCW radar receiver designed in 0.18-μm CMOS exhibits subcentimeter ranging capability from onboard modulation measurement, consuming 26 mW from a 1.6-V supply.