Wide-band hybrid analog/Digital frequency domain adaptive filter

This paper describes a hybrid adaptive filter which employs a cascade of analog forward and inverse Fourier transform processors interconnected via a digital interface. The interface multiplies the transformed input, sample by sample, by a set of weights stored in RAM and compares the products against a desired complex spectrum. The resulting error is used to update the RAM weights via a feedback loop, which forces the multiplied output to converge towards the desired complex spectrum. The use of frequency domain processing in the adaptive filter offers faster, more controlled convergence than conventional time domain adaptive transversal filters. We present simulations and practical results on a frequency domain adaptive filter based on 100 point surface acoustic wave chirp transform processors which give the adaptive filter a 4 MHz real-time bandwidth capability. Thus, this new processor is likely to find potential application in equalization, echo, and interference suppression in high bandwidth communications and radar systems.