Zoom-in frontend for power-efficient high-speed and high-resolution capacitive sensor measurement system

This paper motivates the use of a “zoom-in” front-end stage to remove the effect of a large nominal sensor capacitance of a capacitive displacement sensor, intended for measuring small displacements. In this way, the dynamic range requirement for the following stages, namely the ADC, is greatly relaxed. The designed circuit uses correlated double sampling to cancel both amplifier´s offset and the reset noise. A PCB prototype with standard off-the-shelf components is built up, to verify noise-canceling principle and evaluate the achievable capacitance resolution. An input referred capacitance resolution of 21 aF (rms) is measured, from a capacitive sensor with a nominal capacitance of 10 pF.