Patent ID: 7948244

Claim:
A capacitive sensor including a capacitive sensor output and having a gain stage including a first capacitive element, a second capacitive element, a first operational amplifier, and a gain stage output, the capacitive sensor comprising: an active filtered-sampling stage having an input coupled to the gain stage output, the active filtered-sampling stage including: a first resistive element having an input coupled to the gain stage output and having an output coupled to a first node; a second resistive element having an input coupled to the first node and an output coupled to the capacitive sensor output; and a first switch selectively coupling the first node to a second operational amplifier of an integrator circuit, wherein the integrator circuit is coupled to the capacitive sensor output and wherein during normal operations in which the capacitive sensor is to produce a voltage output proportional to a capacitive difference of the first and second capacitive elements, the first switch is controlled, at a first time, to couple the first node to the second operational amplifier, resulting in the integrator circuit sampling a first signal that includes noise from the first operational amplifier, and the first switch is controlled, at a second time, to decouple the first node from the second operational amplifier, resulting in a second signal that includes noise from the second operational amplifier being subtracted from the first signal so that an output signal produced at the capacitive sensor output includes noise from the first operational amplifier plus noise from the first switch minus noise from the second operational amplifier.