Patent ID: 8878797

Claim:
A capacitance measurement circuit comprising: an external capacitor; an amplifier having an input and an output, the amplifier comprising a feedback capacitor disposed between the input and output, the input of the amplifier coupled to the external capacitor, the amplifier configured to amplify a modulated excitation signal furnished to the input of the amplifier by the external capacitor, the modulated excitation signal modulated according to a capacitance of the external capacitor; and a correlator configured to synchronously demodulate the modulated excitation signal, the correlator comprising a mixing circuit coupled to the output of the amplifier, the mixing circuit configured to multiply the modulated excitation signal by an original non-modulated analog excitation signal to generate a mixed signal, and an integrator circuit coupled to the mixing circuit, the integrator circuit configured to integrate the mixed signal over a discrete period of time to generate an output voltage corresponding to the capacitance of the external capacitor, wherein the period of time is a multiple of 1/f, where f is a frequency of the analog excitation signal.