FIR filter compensator for CIC filter suitable for software defined radio

Software Defined Radio (SDR) supports different wireless standards in a single radio device. This can be done by digital signal processing. In digitized form different wireless standards requires different sample rates for baseband processing. Sample rate conversion (SRC) is required for this purpose. In SRC, Comb-Integrator-Comb (CIC) filter plays an important role. Multistage CIC filter provides better stopband characteristics but passband response deteriorates. A FIR filter cascaded in series with CIC filter provides desired transition band. This paper discusses about basic characteristics and structure of FIR filter. Then it discusses the implementation of FIR filter as decimator and interpolator, poly-phase implementation of FIR filter and shows the simulated response of CIC filter when cascaded with FIR filter. Lastly, it also tries to implement CIC filter efficiently in polyphase representation.