L-Band SiGe HBT dual-band differential amplifiers having frequency-tunable bandpass or bandstop responses using novel varactor-loaded dual-band resonators

TLDR: In this article, a varactor-loaded dual-band resonator comprised of series and parallel LC circuits is employed in the load circuit of differential amplifiers for realizing dualbandstop responses as well as the series feedback circuit for dualbandpass responses.

Abstract: L-band SiGe HBT dual-band differential amplifiers with frequency-tunable bandpass or bandstop responses have been developed for the next generation adaptive and/or reconfigurable wireless radios. A novel varactor-loaded dual-band resonator comprised of series and parallel LC circuits is employed in the load circuit of differential amplifiers for realizing dual-bandstop responses as well as the series feedback circuit for dual-bandpass responses. The dual-bandstop amplifier has presented a lower-bandstop frequency of 0.47 to 0.62 GHz with an upper-bandstop frequency of 1.17 to 1.18 GHz. Meanwhile, an upper–bandstop frequency can be varied from 0.6 to 1.1 GHz for a lower-bandstop frequency of 0.37 to 0.4 GHz. The maximal band-rejection was 17.7 dB. In addition, the dual-bandpass amplifier has achieved a lower-bandpass frequency of 0.37 to 0.5 GHz with an upper-bandpass frequency of 0.61 to 0.63 GHz. Meanwhile, an upper714 Yasushi Itoh and Hiroaki Takagi bandpass frequency can be varied from 0.61 to 1.11 GHz for a lower-bandpass frequency of around 0.36 GHz. The maximal gain was 9.6 dB. The varactor-loaded dual-band resonator presented in this paper is expected to be one candidate for realizing the multi-band amplifier utilized in the reconfigurable wireless transceivers.