A standard CMOS technology fully-analog differential capacitance sensor front-end

In this paper we present an analog electronic interface, developed in an integrated standard CMOS technology, for differential capacitive sensors. In particular, the two cases of hyperbolic and linear capacitive behavior have been considered. The capacitive evaluation can be done by the design and characterization of a suitable electronic circuit which determines the measurand variations through the reading of a voltage. This approach has shown high accuracy as well as other solutions reported in the literature where the capacitances are typically converted into a frequency. The front-end has been designed in a standard CMOS technology (AMS 0.35 um) to work at dual supply voltages (1.65 V each), so to be suitable for low-cost portable applications. Spice simulations on the designed integrated solution and experimental results using a discrete-component prototype have shown a reduced absolute percentage error (lower than 1% and 3.5 %, respectively), if compared to theoretical expressions. Sensitivity and resolution on a practical case study of the sensor/interface system are also given, showing very satisfactory values.