A FORTRAN IV Computer Program for Designing and Implementing Recursive Digital Filters

A FORTRAN IV computer program has been developed that will design and implement recursive digital filters. Standard low pass analog designs are used in combination with the bilinear transform to design the filters. The analog designs used are Butterworth maximally flat, Chebyshev equiripple in the passband, and elliptic equiripple in both passband and stop band. Transformations are possible in the z domain to obtain high-pass, band-pass, and band-stop filters from the low-pass designs. The development of the computer program is detailed along with all the necessary equations. A complete listing of the code also is provided.