Hybrid parallel/cascade structure for designing variable fractional-delay filters

There are two different ways to implement variable fractional-delay (VFD) filters. One is the Farrow structure, which is constructed by connecting differentiators with various orders in parallel, the other one is the first-order differentiator structure, which is constructed by cascading first-order differentiators. The parallel Farrow structure requires a large memory to store filter coefficients but possesses low filter delay, and the cascade first-order differentiator structure requires less memory but results in long filter delay. In this study, a hybrid structure is presented to implement the VFD filter, which considers the parallel and cascade connections of differentiators simultaneously such that the trade-off between memory requirement and filter delay can be made. Some numerical examples are demonstrated to show the effectiveness of the proposed structure.