Active RF bandpass filter with wide frequency tuning range

The paper presents an improved tuning method implemented for a differential active inductor based RF bandpass filter. Derived from a previous designed transistor-only second order filter topology, independent frequency and quality factor tuning are demonstrated in 0.18 mum CMOS technology. The circuit has been basically designed for 2.4 GHz, a frequency high enough to cover the main wireless standards, has small power consumption and can exhibit very high Q values. A wide frequency tuning range is obtained by using on.chip varactors. The circuit absorbs 1 mW from a 1.8 V supply at 2.4 GHz central frequency.