Active polyphase filter analysis

This paper describes the analysis and design of active polyphase filters. Analysis for 1- and 2-stage filters are carried out in this paper with simplified transconductance models. Gain and stability, which differentiate the active and passive filters, are analyzed and presented as a function of the key design parameters of the transconductance element and of the filter. Additionally an analytical expression for the 2-stage stability is presented. A design example is given to demonstrate the use of the analysis results. The work presented provides tools for designing active polyphase filters in terms of gain, stability and image rejection ratio.