Patent ID: 7521942

Claim:
A device for determining a measurable capacitance for proximity detection, the device comprising: a plurality of sensing electrodes; a guarding electrode proximate the plurality of sensing electrodes; a passive network that includes a filter capacitance; and a controller coupled to the plurality of sensing electrodes, the guarding electrode, and the passive network, the controller configured to apply a pre-determined voltage to at least one of the plurality of sensing electrodes using a first switch, apply a first guard voltage to the at least one guarding electrode using a second switch, share charge between at least one of the plurality of sensing electrodes and the passive network such that shared charge is accumulated on the filter capacitance, apply a second guard voltage different from the first guard voltage to the guarding electrode; and measure a voltage on the filter capacitance for a number of measurements equal to at least one to produce at least one result to determine the measurable capacitance for proximity detection.