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

Abstract

This letter presents the application of the f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> -doubler technique, for the first time, to improve the unitygain frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ) of inverse-mode (TM) silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs). An f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> -doubler structure, which used three identical SiGe HBTs with the same emitter area of 0.07 (width) × 0.9 (length) μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , is implemented in a commercial 0.13-μm SiGe-BiCMOS technology platform. A peak f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> of 77 GHz is extrapolated for the TM f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> doubler, whereas a peak f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> of a single TM SiGe HBT is found to be 53 GHz, exhibiting an increase of about 46% in f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> from the f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> -doubler technique. The maximum oscillation frequency of the TM f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> doubler using Mason's unilateral gain is about 158 GHz. Tn addition, small-signal model parameters of the TM f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> doubler are presented, which show the TM f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> -doubler structures can be treated as a single transistor element for highfrequency circuit design.