FPGA-based efficient two-path polyphase multistage half-band decimated and multi-band filters

An efficient multistage decimation low-pass filter (LPF), with narrow passband and very narrow transition band, composed of three-stages of half-band filters is proposed, where the middle stage (two-path two-coefficient polyphase filter) is used repeatedly as decimated cascaded stages. For the last stage, two cascaded two-coefficient filters are used. An efficient field programmable gate array (FPGA) realization of the proposed decimated LPF is compared with a previous one introduced for noise thermometer application and composed of six stages. It is shown that the two-path polyphase filter can be utilized as a half band or a multiband according to the length of the shift registers. The proposed two-path polyphase multiband filter can be used in the realization of a multistage single frequency LPF.