Narrowband Notch Filter Using Feedback Structure Tips & Tricks
The design of a notch filter poses challenges in managing the tradeoff between distortion in the passband and the notch band. The ideal notch filter has a 3-dB notch bandwidth (BW) equal to zero in the notch band and the unity gain in the passband. Therefore, the design objective is to shrink the BW as small as possible while preserving the gain as close to one as possible. The task of a notch filter is to eliminate interference while preserving the target broadband signal. These filters have many applications for narrowband interference removal in biomedical engineering [1], speech processing [2], image processing [3], [4], and communication [5]. In this article, we describe two ways to implement a notch filter. First, we present a simple notch filter and then illustrate why its performance is less than ideal. Next, we present a trick to apply a novel feedback structure to that notch filter, which improves its performance to nearly ideal. With the help of the feedback structure, we obtain an adjustable parameter. By tuning this parameter, different characteristics of the notch filter are obtained due to the change of its poles' position.