Sub-femtofarad capacitive sensing for microfabricated transducers using correlated double sampling and delta modulation

The theory, design, and measured performance of a circuit which measures ve ry small capacitances, particularly suitable for microfabricated sensors re legated to a high parasitic environment, is presented. The circuit uses an existing capacitive sensing ASIC configured as a delta modulator to achieve a sense resolution of 0.53 fF at a 6-kHz sample rate in the presence of bo ard-level parasitics, The applicability of the circuit to microfabricated s ensors has been successfully demonstrated using a bulk-micromachined vertic al transducer that is similar to many pressure sensors and accelerometers.