On the design of very sharp narrowband FIR filters by using IFIR technique with time-multiplexed subfilters

This paper presents an Interpolated Finite Impulse Response (IFIR) method to design narrowband FIR filters with very sharp transition band. The method is based on a multi-stage IFIR scheme, where a multiplierless model filter is used along with several interpolator filters that differ to each other only in their expansion factors. Sharpening technique is applied to the model filter to improve its magnitude characteristics. The Pipelining-Interleaving (PI) technique is applied to avoid the repetitive use of the model filter. Similarly, the folding technique is used to implement only once the arithmetic operations of the interpolators. As a result, the overall filter requires the implementation of fewer arithmetic operations in comparison with the direct design as well as with other similar approaches.