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 insensitive to parasitic capacitances, and can cancel the effects of offsets, low-frequency noise sources, and sampled kT/C noise of the MOS switch used in the topology. It represents a significant improvement in capacitance resolution than previous methods. It is currently being used in the readout circuits of experimental pressure sensor chips containing 100 fF air-gap capacitors with a resolution in the 30 aF range at a sampling speed of 11 kHz.<
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