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 2nd/3rd 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 VCE swing on the upper SiGe HBT in the cascode to beyond BVCBO, 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.