Design of High-sensitivity Micro-Capacitance Detection Circuit

This paper presents a high-sensitivity micro-capacitance detection circuit designed for capacitive micro-displacement sensing. The circuit exploits the virtual short characteristic of the operational amplifier (op-amp) to achieve equipotential driven guard in triaxial cable, thereby mitigating the impact of cable parasitic capacitance. Additionally, the op-amp’s reference ground potential is allowed to float with the potential of the target capacitor, effectively overcoming the influence of parasitic capacitance to ground. Based on a self-developed three-terminal capacitive displacement sensor, it has been confirmed that the circuit possesses the capability to detect micro-capacitance variations at the zeptofarad (zF) level, thereby meeting the detection requirement for nanometer-level displacement resolution within the millimeter range.

I. Introduction

The advancement of ultra-precision manufacturing and contemporary industrial production technology has prompted a pressing demand for high-precision and high-sensitivity micro-displacement detection. Capacitive displacement sensing technology not only features non-contact sensing but also offers advantages such as compact size, high cost-effectiveness, heightened sensitivity, and excellent dynamic response. However, the background capacitance of micro-capacitance sensors mostly falls within the femtofarad (fF) range, resulting in a capacitance change corresponding to nanoscale displacement changes being in the zeptofarad (zF) range only. This small capacitance change can easily be overwhelmed by parasitic capacitance in cables and detection circuits, thereby complicating detection. Therefore, enhancing the signal-to-noise ratio of micro-capacitance detection presents a fundamental challenge that needs to be addressed [1].