Zoom-in front-end circuit for high-performance capacitive displacement sensors

We report an integrated front-end circuit for capacitive displacement sensors, suitable for measuring small displacements, superimposed on a much larger stand-off distance between the sensing and the target electrodes. In order to cancel the effect of the resulting offset capacitance, a circuit technique called electrical zoom-in is applied in the interfacing circuit. The zoom-in front-end can achieve an input referred capacitance resolution of 28 aF (RMS) from a sensor with nominal capacitance of 10 pF with a measurement latency of only 5 us.