A concept of Q-varying continuous-time notch filter with improved dynamic behavior

In many measurement applications, it is required to have notch filters which simultaneously possess a very selective magnitude response (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 new class of continuous-time 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 notch filter are presented and compared to the performance of the traditional Q-constant filter using an ECG signal with unwanted interference as a study case.