DIGITAL CANCELLATION OF NOISE AND OFFSET FOR CAPACITIVE SENSORS

A digital noise and offset cancellation technique for use with charge- redistribution capacitance sense techniques is presented. It is insens itive to parasitic capacitances, and can cancel the effects of offsets , low-frequency noise sources, and sampled kT/C noise of the MOS switc h used in the topology. It represents a significant improvement in cap acitance resolution than previous methods. It is currently being used in the readout circuits of experimental pressure sensor chips containi ng 100 fF air-gap capacitors with a resolution in the 30 aF range at a sampling speed of 11 kHz.