Structures for implementing FIR-filters with an adjustable frequency response

Abstract

The paper deals with the problem of implementing FIR-filters with an adjustable amplitude response and a fixed and linear phase response. Among the various possible structures of an FIR-filter, the Lagrange structure, and especially, the frequency sampling structure are taken into consideration because they offer the potential of easy adjustment of the system function at a certain number of sample points in the z-plane. The widely known original forms of these structures are reviewed together with some forms of a new type. The review is followed by a description of several improved forms which, unlike the original forms, do not contain any IIR-subsystems. In addition the close interrelation between the frequency sampling structure and the discrete Fourier transform is outlined. In the final discussion oneor the other of the improved forms is recommended depending on whether the sample points are spaced uniformly or nonuniformly on the unit circle, and also depending on whether the information for adjusting the system function is provided separately from the input signal or it has to be deduced from the input signal by means of a frequency analysis.