Patent ID: 8618872

Claim:
A method for varying cut-off frequency of a filter when a steady state is disturbed, said method comprising: detecting a trigger event that disturbs said steady state; in response to said trigger event, changing a value of a circuit element of said filter to an initial value to raise said cut-off frequency from a steady-state target frequency to an initial frequency; maintaining said initial value of said circuit element to maintain said cut-off frequency at said initial frequency for a predetermined period after said trigger event; after said predetermined period, comparing a difference, between a current value of said circuit element and a step size, to a target value of said circuit element corresponding to said target frequency; and: (1) when said difference is less than said target value of said circuit element, setting said value of said circuit element to said target value of said circuit element and resuming said steady state, and otherwise: (2)(a) changing said value of said circuit element by said step size to a new value to reduce said cut-off frequency by a frequency step to a new frequency, (b) maintaining said new value of said circuit element to maintain said new frequency for an interval equal to a step length, and (c) after said interval, repeating said comparing, said changing and said maintaining until, in said comparing, said difference is less than said target value of said circuit element and then performing said setting said value of said circuit element corresponding to said target value of said circuit element and resuming said steady state.