Patent ID: 8436693

Claim:
A method for tracking and controlling a resonance frequency of a band-pass filter, said method comprising: sending an input and an output signal into a plurality of frequency modulators, each signal being associated with a phase; down-converting said input and output signal in the plurality of frequency modulators, thereby providing a DC term corresponding to a zero frequency representation of a phase difference between said input signal and a local oscillator frequency and between said output signal and said local oscillator frequency; sending each DC term into one of a plurality of low-pass filters and thereafter to a comparator having an output based on a comparison of phase information of said input and output signals; and tuning the band-pass filter phase using the output of the comparator based on the phase of the input signal, wherein the tuning of the phase of the band-pass filter comprises using a negative feedback control acting on the resonance frequency of the band-pass filter, and wherein the negative feedback control comprises an analogue tuning loop.