Capacitive sensor interface with precision references

This paper presents an investigation on high-precision capacitance measurement techniques which are aimed for capacitive-sensor-based displacement measurement in advanced industrial applications. The paper analyzes the interface structure and the references used in a capacitive sensor interface (CSI), which define the precision of the capacitance measurement. The trade-offs of using different types of references are discussed. Finally, to validate the analysis, a prototype IC is presented and qualified. This prototype achieves a resolution of 17.5 bit for 10 ms conversion time, while consuming 230 μA from a 3.3 V supply. The measured thermal drift of the interface is ~6 ppm/°C.