There are some exceptional cases where the presence of feedback structure may result in finite impulse response. Caution: In most cases, the presence of feedback elements provide infinite impulse response.Due to the presence of feedback elements, the impulse response of the filter may not become zero beyond certain point, but continues indefinitely and hence the name Infinite Impulse Response (IIR) filter. When, the filter structure is characterized by the presence of feedback elements.It provides linear phase characteristic in the passband. The impulse response of such filter dies out (becomes zero) beyond certain point of time and it is classified as Finite Impulse Response (FIR) filter. When, there is no feedback in the filter structure, no poles in the pole-zero plot (in fact all the poles sit at the origin).Two types of filter can manifest from the given transfer function above. In other words, the design process also involves choosing the number and location of the zeros zeros ( ) and poles ( ) in the pole-zero plot. Examples include how much ripples allowed in passband, stop band etc., Tolerance specifications – that specifies how much the filter response is allowed to vary when compared with ideal response.Design specification:Ī filter design starts with a specification. We may have a simple specification that just calls for removing an unwanted frequency component or it can be a complete design specification that calls for various parameters like – amount of ripples allowed in passband, stop band attenuation, transition width etc., The design specification usually calls for satisfying one or more of the following: One has to weigh-in the pros and cons of choosing a filter design by considering the factors discussed here.īefore proceeding to know the secrets of choosing a filter, I urge you to brush up the fundamentals of digital filter design. The mere fact that there exists so many techniques for designing a filter, suggests that there is no single optimal filter design. There exists two different types of Linear Time Invariant (LTI) filters from transfer function standpoint : FIR (Finite Impulse Response) and IIR (Infinite Impulse Response) filters and myriad design techniques for designing them. “What is the best filter that I should use? FIR or IIR ?” is often the question asked by many.

Filter designer test image