A Transformer-Based Front-End Circuit for Grounded Capacitive Sensors with Square-Wave Excitation

This work proposes and experimentally characterizes a novel front-end circuit for capacitive sensors with one electrode grounded, which are quite common in liquid-level and position measurement applications. The circuit relies on a properly shielded custom transformer, as already suggested in the literature, but uses a square excitation instead of a sinusoidal excitation, thus being a simpler solution. Furthermore, the sensor signal is read by a charge amplifier with a single supply voltage, instead of a transimpedance amplifier with a split supply voltage. The preliminary experimental results show an input–output characteristic with a non-linearity error lower than 0.5% FSS in the [0, 33] pF measuring range.