Design method of lowpass IIR digital filters having maximally flat and monotonic passbands, equiripple stopbands and narrower transition band width

摘要

In this paper, a design method of filters having the maximally flat and monotonic decreasing passbands, the equiripple stopbands and the transition bands with far narrower width than these of inverse Chebyshev filters of same order is proposed. The filters are designed in ac-plane of Deczkey and the characteristic functions have a pair of conjugate complex roots whose ordinates are constrained by the monotonic decreasing amplitude of passbands. The degree of freedum of the ordinates of conjugate complex roots is use to minimize the transition band width. The analytical equations giving the minimum width are obtained. Using the above method, the transition band width can be considerably narrowed. In other words, the order of filters decreases to about two thirds or one half of that of inverse Chebyshev filters under the same design specifications.