High-Efficiency SiGe-BiCMOS $E$ -Band Power Amplifiers Exploiting Current Clamping in the Common-Base Stage

This paper proposes high-efficiency E-band power amplifiers (PAs) in SiGe-BiCMOS based on a common-base output stage. A comparison between common-emitter and common-base configurations proves the latter yields higher output power, enhanced linear range, and robustness against self-heating issues. Furthermore, the base-emitter junction of the BJT in common base can be exploited to implement the current-mode version of the well-known diode voltage clamper, so that the dc current tracks the signal current. This yields an improvement of efficiency, particularly in power back-off. Two PA designs are described: a single-path, two-stage amplifier and a second version delivering higher output power with transformer-based power combining at minimal efficiency degradation. At 80 GHz, the two PAs deliver 18-and 20.5-dBm OP
_{1 dB}
and 19- and 21.5-dBm P
_sat
. The PAE at OP
_{1 dB}
is 22% and 20%; at 6-dB back-off, it is still 8.5% and 7.2%, respectively. The prototypes demonstrate two- three times higher PAE compared to previously reported silicon PAs with similar output power at the E-band.