Phase linearity in polyphase filters

Polyphase structures composed of recursive filters as subsections can be made to have either approximately linear or nonlinear phase response depending on the requirements of the application. There are several ways to obtain approximately linear phase filters. In this paper, we are concerned with the phase deviation from linearity in polyphase filters composed of infinite impulse response allpass sections. A linear relationship is presented between the number of delay sections per branch and the phase deviation from linearity which allows the designer to know how many nonzero sections are needed per branch in order to obtain a certain deviation from linearity beforehand