New Concept of Delay Equalized Low-Pass Butterworth Filters

One of the important problems of the analog signal processing is to design the filters which possess linear phase response in the frequency domain and at the same time the sharpness of the step response in the time domain. This paper presents theoretical concept of time-varying Butterworth filters with equalized group delay response. The compensation of the phase response is carried out with the aid of the allpass filter which is cascade-connected to the structure of the classic Butterworth filter. Time-varying coefficients were introduced to the phase-compensated filter structure for the purpose of minimization of the filter transient state. This paper contains simulation results of the proposed filters, solution of the undershoot problem, and comparison with the classic circuits