Synchronous Demodulator for Autonomous Sensors

A novel differential synchronous demodulator is presented that uses the on-off switching characteristic of the power supply in autonomous systems as control signal for demodulation. The proposed circuit, which uses a single op amp and SPDT switch, can be useful in sensors networks or distributed data acquisition systems involving ac sensors or impedance measurements. A prototype demodulator yields a nonlinearity of 0.8% FSR and CMRR = 47 dB at 15 kHz for unity gain. The feasibility of the circuit when supplied by a piezoelectric energy converter is also verified