Filter analysis in the quadratic DDC structure

Abstract

This paper introduces a quadratic Digital Down-Conversion (DDC) structure which moves Intermediate Frequency (IF) signal to baseband by two steps. Firstly, IF signal is moved to baseband nearby with the help of a structure based on polyphase filter, which places mixers after polyphase filters. Then, the signal is moved to baseband through conventional orthogonal frequency mixing. This presented architecture can reduce filter resources and effectively reduce the sample rate and process cost. The implementation structure of the polyphase filters is particularly derived, as well as the constrains on the input signal. Finally, simulation results are presented to illustrate the validity of the new structure.