FPGA implementation of adaptive heterodyne filters

A tunable heterodyne filter makes use of the heterodyne process to create a tunable notch filter from a fixed coefficient high-pass filter. Through the use of a simple second-order IIR band-pass filter to detect the narrow-band interference, it is possible to generate a signal that can be used to see the heterodyne frequency to match the tunable heterodyne notch filter to the center of the detected interference. The result is a single-chip adaptive heterodyne notch filter that can adapt a very high order notch filter to the center of the narrow-band interference to substantially attenuate the interference.