Digital notch filter with time-varying quality factor for the reduction of powerline interference

Many applications require notch filters which possess both a very selective magnitude response (i.e. high quality factor Q) and a transient response of short duration. However, increasing the quality factor also increases the duration of the transient process in the filter after the action of the excitation. This paper presents a concept of digital IIR notch filters whose quality factor changes with time. Owing to a temporary change in the value of the quality factor, the transient can be considerably reduced. Simulations verifying the effectiveness of the proposed Q-varying IIR notch filter are presented and compared to the performance of the traditional filter with constant Q using ECG signal with unwanted 60-Hz powerline interference as a study case.