A filter was designed for use either in narrowband or UWB system by switching the function. In the NB function, the filter performs as a channel select filter at 5.25GHz with adjustable gain and BW. In the UWB function, the filter acts as an LNA from 3.6-10.1 GHz with the capacity of eliminating the 5.25GHz NB interference signal. The design uses the mainstream 0.18 mum CMOS technology. The filter consumes 27 mW at 1.8V supply and exhibits a good performance in both functions. This filter allows the same receiver front- end to provide NB or UWB service and reduces system complexity and cost.