Infinite Impulse Response Filters

In this chapter, Infinite Impulse Response Filters, another type of filter called the IIR filter is designed and analyzed. This type of filters requires less number of coefficients for the same specification. However, it is susceptible to instability. This type of filters is developed from the basic resistor-capacitor lowpass filter for clear understanding of the filtering process. The idea is that the transfer functions of families of analog filter have been designed with different characteristics. These transfer functions can be transformed to those of digital IIR filters. The bilinear transformation is most often used in designing digital IIR filters. While the range of the frequency of the components of continuous signals is infinite, the frequency range is restricted in digital filters due to sampling. This creates a problem called warping. Still, practical filters can be designed using the transformation method. In this chapter, examples of design of lowpass, highpass, bandpass and bandreject filters are presented.