High-speed tunable fractional-delay allpass filter structure

By using a fractional delay (FD), a filter can perform various operations such as asynchronous sample rate conversion, synchronization of digital modems and sound synthesis of musical instruments. An IIR tunable FID filter can be designed using Thiran-based FD allpass filter structure. However, this IIR structure has the disadvantage of long critical path and large hardware overhead. In this paper, a modified Thiran-based FD allpass filter structure is proposed. Compared with the existing structure, the proposed structure requires shorter critical path, less hardware complexity and improved frequency characteristics.