Chapter 17 - Iir filter design

Abstract

Infinite impulse response (IIR) filters require fewer delay elements, adders, and multipliers for a given frequency response. Therefore, they are more efficient than finite impulse response (FIR )filters. The disadvantage of IIR filters is their nonlinear phase response. A non-constant group delay means that all frequencies do not experience the same delay. Thus, impulses containing components with a wide range of frequencies will be distorted when passed through an IIR filter. Most IIR filters are designed using an analog filter model. Analog filter models are the familiar Butterworth, Chebyshev, Cauer, Inverse Chebyshev, and Bessel types. Bessel models are not converted into digital filters. The advantage of a Bessel response in an active or passive linear filter is the constant group delay, at the expense of a poor skirt response. FIR filters can produce a constant group delay with far superior skirt response, so they are used where group delay is important.