We know that there are two types of digital filters i.e., FIR and IIR. The design procedures of IIR filter are the extensions of design procedures developed for analog filters. To replace the existing analog filters, the IIR filters are generally used.
The following approximations are carried out for deriving the discrete-time transfer function HD(z) of IIR digital filters from continuous-time transfer function HA(s) analog filters:
The following are the realizability constraints on Transfer function HD(z) :