Narrowband Variable Digital Filters with Independently Tunable Characteristics and Minimum Number of Tunable Elements
Georgi K. Stoyanov, Ivan M. Uzunov, Masayuki Kawamata · 1998
Abstract — A new approach to design variable IIR digital fil-ters by using a cascade of equal first- or second-order low-pass filter sections is proposed in this paper. These sections are designed in a way that the cutoff frequency of the resul-ting filter can be tuned by recalculating and changing only a single parameter value. And as there is no any approximate representations of the coefficients, tuning is not limited by magnitude degradations typical to the other known methods. The necessary approximation methods for such design are developed and step-by-step procedures for their application are proposed. Then the realizations of first- and second-order filter sections, permitting independent tuning of the cutoff frequency, are discussed and design methods are derived. Other then lowpass filters are easily obtained through fre-quency transformations. Finally, experimental results, validating the proposed design procedures and demonstrating the superiority of the new method, are given. 1.