Differential synchronous demodulator for conductivity sensors

We present a novel differential synchronous demodulator intended for signal conditioning in a network of conductivity sensors for water quality monitoring. The proposed circuit merges the demodulating and low-pass filtering stages in a single integrator stage and yields the quality performance inherent to coherent demodulation with the added advantages of compactness and low-cost. In the range from 1 kHz to 10 kHz, the common mode rejection ratio is better than 70 dB and the signal-to-noise ratio exceeds 70 dB.