Comparative analysis of four second-order OA-RC polyphase filters for an ISM Low-IF receiver

This paper presents the comparative analysis of four implementation of a polyphase filter with the IF frequency of 1MHz and the passband width of 700 kHz. All versions employ the OA-RC technique but have different topologies: the classical structure based on lossy integrators, then two structures derived from the well-known Tow-Thomas and Sallen-Key real biquads and a novel topology, based on the Rauch structure. First, the requirements for the active cell - the OA - are derived by analysing the effects the OA finite gain-bandwidth product and (possible large) output resistance has on the filter performance for each topology; then an OA that meets the requirements is designed in a standard 0.18um CMOS process, optimized for low power consumption. The extensive set of simulation results presented here allows a detailed comparison between the four designs, targeting same specifications.