Patent ID: 7584235

Claim:
A filter having a variable passband comprising: a filter circuit having as inputs a signal to be filtered (a forward signal) and a reverse version of the signal to be filtered (a reverse signal), and having as an output a filtered signal as a function of a variable coefficient; and a variable equivalent sample rate coefficient converter having an initial coefficient as an input together with a variable resampling rate parameter that determines the variable passband, and providing as an output the variable coefficient as a function of the variable resampling rate parameter; wherein the filter circuit comprises: a first IIR filter having the forward signal and the variable coefficient as inputs, and providing as an output a first filtered signal; a second IIR filter having the reverse signal and the variable coefficient as inputs, and providing as an output a second filtered signal; and means for combining the first and second filtered signals with the forward signal to provide the filtered signal; wherein the combining means comprises a summing circuit having as inputs the first and second filtered signals and the forward signal, and providing as an output the filtered signal; and wherein each IIR filter comprises: a gain stage having an input coupled to receive an input signal, and providing an output in response to a gain component of the variable coefficient; and a decay stage having an input coupled to the output of the gain stage, and providing as an output a filtered input signal in response to a decay component of the variable coefficient.