New class of recursive digital filters for decimation

A class of equiripple IIR (Infinite Impulse Response) digital filters, with all zeros on the unit circle is discussed. These new filters bring together, to some extent, the advantages of FIR and elliptic designs, by having only powers of z^Din the denominator (D is the decimation ratio). Only every Dth output is computed with these recursive filters. Comparisons are made with FIR and elliptic designs. It is shown that these new filters require significantly fewer multiplications per second. Coefficient storage requirements of these three designs are also compared. Some interesting properties of filters with only powers of z^Din the denominator are briefly discussed.