A Single-Chip Single-Antenna Radar for Remote Vital Sign Monitoring

This article proposes an effective way to use self-injection locking (SIL) in a radar system to detect human chest cavity movement for vital signs monitoring with minimal hardware. The proposed approach expands the idea of using a phase-locked loop (PLL) system as a demodulator and a single antenna, making the system more compact. The system includes ON-chip dc offset cancellation for system initialization. This work investigates and compares an $LC$ -based voltage-controlled oscillator (LCVCO) and a ring voltage-controlled oscillator (RVCO) in terms of primary sensitivity for motion detection and phase noise. A study of injection-locking of both the LCVCO and RVCO is also established. The study shows that the RVCO is superior to the LCVCO in terms of sensitivity while the phase noise does not differ significantly as the frequencies of interest are very small, i.e., heart rate and respiration are bandwidth-limited to a few hertz. To verify the proposed idea, a design of both systems, an LCVCO-based PLL and an RVCO-based PLL, was implemented in 65 nm CMOS technology at 1.5 GHz. The simulation and measurement results confirm the idea proposed: the RVCO shows better performance across all metrics, e.g., higher sensitivity by 4 dB, lower power consumption by 30%, and reduced area (almost half) compared to the LCVCO.