An X-band inverse class-F SiGe HBT cascode power amplifier With harmonic-tuned output transformer

This paper presents a highly efficient X-band inverse class-F SiGe HBT cascode power amplifier (PA) to overcome performance limitations imposed by device breakdown. Simultaneous fundamental and 2
^nd
/3
^rd
harmonic matching is achieved using an output transformer with an embedded capacitor at its center-tap, which enables inverse class-F operation. Use of a cascode topology with a low base impedance termination and minimum voltage-current waveform overlap extends the V
_CE
swing on the upper SiGe HBT in the cascode to beyond BV
_CBO
, boosting output power and power added efficiency (PAE). As proof of concept, the inverse class-F PA was implemented in 0.13-μm SiGe BiCMOS technology. Measured results show an output power of 25.8 dBm and 51.1% peak PAE at 10 GHz, when operated on a 3.0 V supply. To the authors' best knowledge, our work has the highest efficiency among all Si-based X-band PAs with comparable output power.