ADAPTIVE DIGITAL NOTCH FILTER DESIGN ON THE UNIT-CIRCLE FOR THE REMOVAL OF POWERLINE NOISE FROM BIOMEDICAL SIGNALS

This paper investigates adaptive digital notch filters for the elimina tion of powerline noise from biomedical signals. Since the distributio n of the frequency variation of the powerline noise may or may not be centered at 60 Hz, three different adaptive digital notch filters are considered. For the first case, an adaptive FIR second-order digital n otch filter is designed to track the center frequency variation. For t he second case, the zeroes of an adaptive IIR second-order digital not ch filter are fixed on the unit circle and the poles are adapted to fi nd an optimum bandwidth to eliminate the noise to a pre-defined attenu ation level. In the third case, both the poles and zeroes of the adapt ive IIR second-order filter are adapted to track the center frequency variation within an optimum bandwidth. The adaptive process is conside rably simplified by designing the notch filters by pole-zero placement on the unit circle using some suggested rules. A constrained least me an-squared (CLMS) algorithm is used for the adaptive process. To evalu ate their performance, the three adaptive notch filters are applied to a powerline noise sample and to a noisy EEG as an illustration of a b iomedical signal.