On finding the degree of an elliptic function filter
L.F. Lind · 1988
Describes a method to find what degree of elliptic function filter is necessary to meet a given specification. Although there are graphical methods for finding the degree (L.R. Rabiner et al. 1975), there does not appear to be any simple formula in the published literature which performs this computation. Although a simple computable formula for the degree of elliptic filters is not known, a simple algorithm has been found, and is presented below. The algorithm features: brevity, speed, robustness, and accuracy to at least eight decimal places. The method is based on a modification of the successive conformal mapping method of S. Darlington (1978), which avoids the explicit use of elliptic functions. The algorithm is realised with a simple BASIC program (listed in the appendix). It can also be implemented with a programmable or nonprogrammable hand-held calculator.