Patent ID: 7710205
Filing Date: 2010-05-04
Classification: G01R

Abstract:
1. A circuit for detecting a capacitive device comprising: an oscillator that generates an output signal, wherein the output signal is substantially periodic, and wherein the oscillator comprises a capacitor that is selectable through a first multiplexer to allow for adjustment of a period of the output signal; a first circuit path connected to an output of the oscillator, wherein the first circuit path comprises a first comparator having an input and an output; and a second circuit path connected to the output of the oscillator, wherein the second circuit path comprises a second comparator having an input and an output, and wherein an electrical phase of the output signal from the oscillator is substantially equal at an input to the first circuit path and an input to the second circuit path; a second multiplexer that selects the capacitive device to electrically connect the capacitive device between the input of the second comparator and ground, wherein, when the capacitive device is selected through the second multiplexer, the output of the second comparator is phase-shifted with respect to the output of the first comparator, and wherein, when no capacitive device is selected through the second multiplexer, a phase of the output of the first comparator is substantially the same as a phase of the output of the second comparator; and a phase shift detector that compares the phase of the output of the first comparator to the phase of the output of the second comparator.