Flat passband and equiripple stopband approximation for lowpass IIR filters with wideband maximally flat group delay

摘要

This paper describes a design method of wideband maximally flat group delay (MFD) lowpass IIR filters with flat passband and equiripple stopband responses. MFD polynomials can straightforwardly provide wideband constant delay characteristics by setting constant delay parameters negative. Total amplitude characteristics are satisfactorily obtained by several alternative interations of flat passband and equiriplle stopband approximation. In the equiripple stopband approximation, an approach of deriving the equiripple function through the allpass function in another complex plane is used.