Adaptive Notch Filters Using A Complex Heterodyne Approach

Two techniques have been recently proposed for implementing tunable notch filters using a complex heterodyne approach. Both techniques rely on the rotating of poles and zeros in the z-plane much like a simple combination lock: clockwise once, counter-clockwise twice, then clockwise once. In the first approach, all of the poles and zeros are rotated; in the second approach, the upper semi-plane poles and zeros (positive poles and zeros) are rotated separately from the lower semi-plane poles and zeros (negative poles and zeros). Both standard arithmetic and residue number arithmetic (RNS) implementations have been suggested. In this paper we show how these tunable complex heterodyne notch filters can be turned into adaptive notch filters suitable for communications and control systems applications. A simple detection circuit is proposed to identify the interference signal to be attenuated and a specialized numerically controlled oscillator (NCO) is proposed to interface between the detection circuit and the tunable complex heterodyne notch filter. The result is an adaptive notch filter with outstanding attenuation and tuning properties.