Low sensitivity active filters with predetermined group delay and Chebyshev stopband attenuation†

Abstract

This paper presents a now class of transfer functions of odd degree with a controllable passband delay distortion and equal-ripple stopband attenuation which arc characterized by a low value of dominant pole Q factor. These functions are obtained by combining the technique of increasing critical polo multiplicity with a special typo of equal ripple approximation to a constant group delay, referred to as the constrained Chebyshev delay approximation. The stopband magnitude performance is improved by adding real frequency transmission zeros which do not affect the phase but completely suppress the output at some frequencies. When compared with the unconstrained equal-ripple delay approximant of Abele, the polynomial in the denominator of the rational transfer function provides an extra degree of freedom which enables one either to increase the roll-off of the attenuation characteristic in the transition region, or to improve the time-domain performance of the resulting network. Tables are presented which in...