Closed-form design of tunable fractional-delay allpass filter structures

Controllable fractional delay (FD) elements are needed in numerous applications, e.g., in timing adjustment of digital receivers, where the received signal is usually not sampled in synchronism with the incoming data stream-the optimal sampling is obtained by interpolation. Tunable FD structures have been known only for FIR filters, most notably the Farrow structure. In this paper we introduce a computationally efficient, tunable FD allpass filter structure. The polynomial coefficients are obtained in closed form using the Thiran allpass filter design method with modifications which completely eliminate the division operations