1.29-W/mm² 23-dBm 66-GHz Power Amplifier in 55-nm SiGe BiCMOS With In-Line Coplanar Transformer Power Splitters and Combiner

This letter presents a four-way parallel-series power amplifier (PA) in 55-nm SiGe BiCMOS with in-line coplanar transformers for output power combining, and input/interstage power splitting. The in-line geometry allows an area efficient impedance matching design and an effective input signals routing to the individual PA stages without phase mismatch. The measurements show that the PA delivers a maximum output power of 23.4 dBm, an output-referred P1dB of 20 dBm, a gain of 23.8 dB, and a maximum power added efficiency of 12.5%, at 66 GHz, with a record power density (output power/active area) of 1.29 W/mm² among PAs on silicon technologies operating beyond 40 GHz.