Multiple branch FIR filters for sampling rate conversion

A class of linear-phase finite impulse response (FIR) digital filters for sampling rate conversion is introduced. These filters consist of two cascaded parts. The first part is a parallel connection of two or three branches with transfer function of the form A _k(z)B_k) (z^D), where D is the sampling rate conversion ratio. The second part has a transfer function of the form C(z^D). The advantage of these designs is that they provide a significant reduction in the multiplication and addition rates as well as in the number of required multipliers over the equivalent conventional direct-form designs also in cases where D is a prime number. In these cases, the sampling rate conversion cannot be performed in several stages and many of the other existing designs lose their advantages. Special multiplier-free solutions are generated for implementing the filters A_k(z), resulting in dramatic savings. Several examples are included showing the efficiency of the proposed filters compared to other existing designs