An ultra-low-power front-end for differential capacitive sensors

In this paper, we present a simple, compact and low-power interface for differential capacitive sensors with direct digital output. The complete system is composed with a current to voltage amplifier, an integrator, a comparator and a feedback capacitor connected in parallel with one of the two capacitances. Overall a Sigma-Delta modulator is obtained that is able to deliver directly a bit stream proportional to the differential capacitance.