Synchronous demodulator for autonomous sensors

In this paper, a novel differential synchronous demodulator is presented that uses the ON–OFF switching characteristic of the power supply in autonomous systems as the control signal for demodulation. The proposed circuit, which uses only an op amp and a double-pole double-throw switch, can be useful in sensor nodes for sensor networks or distributed data-acquisition systems involving ac sensors or impedance measurements. Three prototype demodulators have been implemented using op amps with different power-bandwidth characteristics, and their common-mode rejection ratio (CMRR), nonlinearity, and initial transient were characterized. The working of the circuit when supplied by a piezoelectric energy converter is also verified.