Design and Characterization of an MMIC Current Mode Outphasing Power Amplifier

This paper presents a power amplifier architecture based on outphasing. Both active devices are operated as current sources loaded by a single-ended load. The combination of phase and amplitude control allows for maintaining a constant voltage and, therefore, high efficiency on the devices’ output. Output series compensation reactances reduce the imaginary part of the modulated load and improve efficiency. An integrated circuit prototype, fabricated using 0.25µm GaN-on-SiC technology, whose size is 2.3mm × 2.8 mm, achieves a bandwidth of 1.6 GHz centred at 3.35 GHz, whereas the maximum CW output power remains within 43dBm ± 0.5 dB. A total gain of more than 12 dB is reported from 2.95 to 3.95 GHz, while a maximum Power Added Efficiency (PAE) was measured as 68.5% at 3.25 GHz and remains greater than 60% from 2.85 to 3.8 GHz, and above 50% for almost the entire frequency range. The Output Back-Off (OBO) efficiency peaks at 3.25 GHz with 53.5% and 45.6% for 6 dB and 8 dB back-off, respectively, and remains above 30% and 23.7% for the entire frequency range. An ACPR performance of -45 dBc and -45.3 dBc was obtained for a 100MHz 5G NR signal with 8 dB and 11 dB PAPR, respectively. The average output power was measured as 34.8dBm and 29.4 dBm, while maintaining an average efficiency of 50.5% and 30.4%.