An active 2ndorder band-pass polyphase filter for image rejection with a passband at the carrier frequency fc, stopband frequency at –fc and 40 dB/decade slope is depicted in the Figure. Applications include IF filtering of the I/Q phases, complex subsampling, Hilbert transformation etc. Conventional 2ndorder band pass exhibit only 20 dB/decade slope while not supporting image rejection capabilities.
The design procedure starts with an equivalent low pass filter, which is shifted by the carrier frequency fc as shown in the figure. A filter modeler and SPICE compatible netlist can be downloaded below. More information in: D. Maier, H.-G. Brachtendorf, “Design of an Active 2nd-Order Polyphase Filter for Image Rejection in Subsampling Receivers”, IEEE International Conference Radioelektronika, Prague, 2018.
