High-Linearity Front-End Circuit for Remote Grounded Capacitive Sensors

This article presents a novel front-end circuit for remote grounded capacitive sensors. The circuit is insensitive to amplifier input capacitance and stray interconnecting-cable capacitances. It does not rely on neutralization or compensation techniques that require manual adjustments and high-accuracy reference components. The proposed solution reduces the circuit input capacitance below a few femptofarads using a simple but properly shielded custom transformer. In addition, the circuit keeps a nonlinearity error below 0.01% when measuring capacitances of units or tens of picofarad, even with up to 12-m interconnecting cables.