A 10–17 GHz Continuously Tunable CMOS Filter With Flexible Bandwidth Control Based on Mode-Switching Inductors

A continuously tunable on-chip CMOS bandpass filter with controllable bandwidth based on mode-switching inductors (MSIs) is proposed in this letter. To increase the frequency tuning range of on-chip CMOS filter and improve filter selectivity, MSIs, and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i>-enhancement technology are adopted in the filter design. 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 the low and high frequency band, thus continuously covering 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 MSIs. 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.