A 10-17 GHz Continuously Tunable CMOS Filter with FlexibleBandwidth Control Based on Mode-Switching Inductors

A continuously tunable on-chip CMOS bandpass filter with controllable bandwidth based on mode switching inductors is proposed in this paper. To increase the frequency tuning range of on-chip CMOS filter and improve filter selectivity, mode switching inductors and Q-enhancement technology are adopted. With the proposed mode-switching techniques, the inductance can be switched between different inductance without introducing any extra loss. As a result, the filter can work in a wide frequency tuning range. In addition, flexible control of the filter bandwidth is achieved by loading a varactor between the primary coil and the secondary coil of mode-switching transformer formed by two modeswitching inductors. The equivalent coupling coefficient of the mode switching transformer before and after loading the varactor is carefully analyzed to achieve the desired filter bandwidth. To verify the proposed structure, a 10-17 GHz continuously tunable filter is designed, fabricated, and measured based on 65 nm CMOS technology.