A Novel CPW Balanced Distributed Amplifier Using Broadband Impedance-Transforming MEMS Baluns

Abstract

Abstract – A novel balanced distributed amplifier (DA) was proposed using novel impedance transforming MEMS baluns. The impedance transforming MEMS balun is matched to 50Ω at one input port and 25Ω at two output ports. It is based on the electric field mode-change method, thus it is strongly independent of frequency and very compact. The novel balanced DA consists of two 25Ω-matched DAs and these are combined by 50Ω-to-25Ω baluns. Theoretically, it has two times wider bandwidth and power capability than the conventional DA. So as to verify the proposed concept, we designed and fabricated a conventional DA and the proposed one using 0.15-µm GaAs pHEMT technology. Keywords: MEMS, Balun, Balanced, Distributed amplifier, CPW 1. Introduction The principle of distributed amplifier (DA) was proposed by Percival in 1936 [1]. This new concept made it possible to obtain amplification over much wider bandwidth than conventional amplifier circuit techniques. For a larger power capability, a balanced structure combining two unit DAs with a power divider/combiner is suggested [2]. The authors designed wideband 180˚ hybrid coupler whose bandwidth is from 5 to 11GHz and fabricated a 5-11GHz balanced distributed power amplifier. However, the combining structures cannot have the bandwidth as wide as the DA. Recently, a mode-change impedance transforming balun using a MEMS overlay structure is proposed [3]. This balun is matched to 50Ω at one input port and 25Ω at two output ports and has extremely wide bandwidth. In this report, we proposed a novel balanced DA topology combining two 25Ω-matched DAs with this impedance transforming ultra broadband MEMS baluns of [3]. This novel balanced DA structure shows the possibility of overcoming the limitations of a conventional 50Ω-matched DA.