Patent ID: 8643619
Filing Date: 2014-02-04
Classification: G01D,G01R,G06F

Abstract:
1. A capacitance measurement circuit comprising: an external capacitor; and a coherent detection circuit coupled to the external capacitor and configured to measure a capacitance of the external capacitor and to convert the measured capacitance to a corresponding voltage output, wherein the coherent detection circuit comprises a programmable impedance element, a first amplifier coupled to an output of the programmable impedance element, and an integrating feedback capacitor coupled to an input of the first amplifier and to an output of the first amplifier; and a signal generator coupled to the external capacitor, wherein the signal generator is configured to generate an analog excitation signal that is modulated by the capacitance of the external capacitor, wherein the modulated analog excitation signal is input to the programmable impedance element, and wherein the programmable impedance element is programmed with a time-varying conductance according to a programmed waveform such that a mixed analog signal output from the programmable impedance element is a product of the modulated signal and the programmed waveform.