Noise analysis and characterization of a charge-balancing-based capacitive sensor interface with a resistive reference

This paper presents a detailed noise analysis of a charge-balancing capacitive sensor interface (CSI) based on a resistor-capacitor (R-C) comparison. The CSI was proposed in [1] and [2] and shows superior precision and stability, due to the precision off-chip resistive reference used. In this work, an in-depth noise analysis is presented which provides optimal criteria for the CSI design. The result is applicable for all CSIs with a similar structure. Based on this analysis a prototype CSI is designed and tested, which delivers 17.5-bit resolution in a conversion time of 10 ms. The measurement results show good match with the theoretical analysis.