Robust Notch Filtering by Combining Adaptation in both Time and Frequency

A fully adaptive infinite impulse response (IIR) notch filter has been proposed before with a very good tracking property over a certain frequency range (Torres and DeBrunner, 1998). It is shown that when the frequency to be notched is closed to DC or the Nyquist frequency (f_n) the performance of the IIR notch filter is degraded. A finite impulse response (FIR) notch filter with equal number of coefficients exhibits a reversed performance: the tracking performance is worse than the IIR notch filter in those frequencies far from DC and f_n but better than the IIR notch filter in those frequencies close to either DC or f_n. Hence, a combination of these two filters is proposed in this paper to improve the tracking performance of the notch filter over the total range of frequencies. Computer simulations show the improved performance of the combined adaptive filter. The design is also simple in computation and robust in tracking a time-varying sinusoidal signal.