Investigation of f(T)-Doubler Technique to Improve RF Performance of Inverse-Mode SiGe HBTs

Abstract

This letter presents the application of the f(T)-doubler technique, for the first time, to improve the unity-gain frequency (f(T)) of inverse-mode (IM) silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs). An f(T) -doubler structure, which used three identical SiGe HBTs with the same emitter area of 0.07 (width) x 0.9 (length) mu m(2), is implemented in a commercial 0.13-mu m SiGe-BiCMOS technology platform. A peak f(T) of 77 GHz is extrapolated for the IM f(T) doubler, whereas a peak fT of a single IM SiGe HBT is found to be 53 GHz, exhibiting an increase of about 46% in f(T) from the f(T)-doubler technique. The maximum oscillation frequency of the IM f(T) doubler using Mason's unilateral gain is about 158 GHz. In addition, small-signal model parameters of the IM fT doubler are presented, which show the IM f(T)-doubler structures can be treated as a single transistor element for high-frequency circuit design.