DESIGN OF 2-DIMENSIONAL PERIODICALLY TIME-VARIANT DIGITAL-FILTERS

This paper discusses a design method for two-dimensional (2-D) periodi cally time-variant digital filters (PTV DFs) whose filter coefficients vary periodically. First, 2-D periodicities for a variation of filter coefficients are considered, From which two and four-phase variations of coefficients are shown to be suitable for practical applications. Then, the input-output relation (transfer function) for 2-D separable- denominator (SD) PTV DFs is derived, which results in a linear combina tion of the baseband input signal and its modulated versions. Finally, in order to approximate given filter specifications, the structure fo r 2-D SD PTV DFs is given and a design method is proposed. It is shown that, compared with the 2-D SD time-invariant DFs, approximation erro r can be reduced with the proposed SD PTV DFs.