A Passive Tunable Matching Filter for Multiband RF Applications Demonstrated at 7 to 14 GHz

This letter presents a general approach to implement a wideband tunable matching filter for multiband radio-frequency applications. The concept is demonstrated for a two-stage bipolar amplifier to achieve a tunable input and output small-signal match to 50 Ω. The filters are realized as π-networks with two fixed inductors and a 4-bit digitally tuned capacitor based on CMOS switches. The utilized technology is a 130-nm SiGe BiCMOS process. A total frequency tuning range of 7-14 GHz with at least 8-dB return loss and 16.5-20 dB gain is confirmed by measurements and aligns well with the theoretical predictions and simulation results. In addition, a compact analytic theory for the proposed network is derived to extend this approach to arbitrary frequencies and bandwidths.