The paper discusses three approximations of IIR periodically time-varying (PTV) digital filters. Two conventional approximations, i.e. time-invariant difference equation and PTV difference equation approximations are first reviewed. It turns out that computation and hardware complexity of the two approximations is in proportion to the period. To reduce the computation and hardware complexity of the two approximations, an efficient PTV difference equation approximation based on extended Pade approximation is proposed. With this approximation, the given frequency-domain specifications are approximated by a difference equation with PTV coefficients. How to design the difference equation and how to determine the order of the difference equation to obtain the desired approximation precision are considered. A design procedure for the difference equation is presented. As an application of the proposed approximation, a four-channel TDM-FDM transmultiplexer is simulated. It shows that the proposed PTV difference-equation approximation obtains satisfactory precision and compares favourably with above two approximations in respect of computation and hardware complexity.
ASJC Scopus subject areas
- Electrical and Electronic Engineering