An infinite impulse response filter(IIR) is one whose impulse response goes on forever. Recursive filters are closely associated with IIR filters but are not exclusively IIR. The transfer function of an IIR filter is shown below. For it to be IIR, at least one of the a's in the denominator must be non zero. M, the number of zeros should be less than N, the number of poles.

COPYRIGHT © 1999 Cuthbert A. Nyack.