A METHOD OF DESIGNING IIR DIGITAL-FILTERS BY MEANS OF INTERPOLATION TAKING ACCOUNT OF TRANSITION BAND CHARACTERISTICS

The authors recently proposed a design method of stable IIR digital fi lters based on the interpolation by rational characteristic functions of filters, for a set of values of these characteristic function and, in addition, their higher derivatives prescribed at a number of freque ncy. This method can be further extended so that, despite usage of a l ess number of interpolation points, almost the same filter characteris tics as one obtained by the former method can be realized. This paper presents an improved design method for making the transfer function me et strict magnitude specifications. The method proposed in this paper is especially efficient for designing a filter whose characteristics i s specified not only in the passband but also in the transition band w ith relatively narrow bandwidth.