Versatile Sensor Front End for Low-Depth Modulation Capacitive Sensors

Low-depth modulation capacitive sensors, i.e. sensors where the capacitance variations caused by a measurand are only a small fraction of the total capacitance, are frequently encountered in measurement problems. Furthermore, also a conductance (e.g. due to parasitic conductive staining) between the sensor electrodes may affect the capacitance evaluation. We have implemented a capacitive sensor interface in a 0.25 mum CMOS process capable of measuring both conductive and capacitive coupling. The sensor interface provides an offset capacitance compensation and an offset conductance compensation such that a low-depth capacitance modulation can be mapped onto the full scale range of an analog to digital converter. Experimental results for a prototype sensor interface with a capacitive slider array are presented.