A Crystal-Less Embedded Cardiorespiratory Radar System With Duty-Cycled and Pulse-Based Detection for Vital Signs

A duty-cycled and pulse-based embedded radar system without a quartz crystal unit is presented for cardiorespiratory monitoring. A reference clock source with features of high accuracy and temperature independence is directly gained from ac electric power grids. The 50/60 Hz power-line interference is further utilized and converted to a reliable clock source as a substitute for the conventional crystal that can be fed into the radar system. The theoretical analysis of the clock source conversion circuit and the experimental instantaneous frequency deviation from the wall outlet will be described to investigate frequency stability and uncertainty based on statistical evidence and significance. In addition, a pulse control unit (PCU) with a duty-cycle mechanism is implemented to convert the initial clock into a duplet-pulse sequence with a tunable phase delay for simultaneously performing the probing and demodulated pulses. A fully customized embedded radar system driven from a 60 Hz ac source is proposed for real-time physiological detection.