A novel interface architecture for differential capacitive sensors

In this work, we propose an analog fully differential interface for capacitive sensors. The working principle of the proposed solution is based on an auto-balancing bridge topology entirely formed by capacitive components. In particular, two capacitors form the sensor, while other components are voltage-controlled capacitors (VCCs) which in steady-state conditions follow sensor capacitor values through a negative feedback performing the zero-convergence of the differential output at the bridge. Theoretical curves involving VCCs control voltages have been extracted and compared with experimental values on a discrete component printed circuit board (PCB), showing very good agreement. The effect of parasitic capacitances have been also considered from evaluations on the PCB, obtaining that their contribution increases if the reference baseline capacitance of the auto-balanced bridge decreases. This study opens to further investigations about modeling and compensation of these capacitance sensors.