The World of Ripples
Pavel Zahradník, Miroslav Vlček · IEEE Circuits and Systems Magazine · 2019
Approximation techniques are useful in numerous engineering and non-engineering tasks. In electrical engineering and in the filter design in particular, approximation techniques allow to approximate in some sense a desired, usually an ideal, but not feasible frequency response of a filter. Among various approximations, polynomial approximations are very useful. The design of feasible linear digital filters with finite impulse response is based on them. There emerge two unique types among polynomial approximations, a maximally flat approximation and an equiripple approximation. We review here the polynomial equiripple approximation, its highlights, applications, history, evolution and latest achievements including open questions.