RF class-S power amplifiers: State-of-the-art results and potential

This paper reports recent results on a current-mode class-S power amplifier for the 450 MHz band, based on GaN-HEMT MMICs. We achieve a peak output power of 8.7 W for a single tone at 420 MHz, encoded in standard band-pass delta-sigma modulation with 1.68 Gbps sampling frequency. The respective efficiency is 34%. We find that these values strongly vary with coding efficiency of the modulation and reach 19 W with 59% for square-wave excitation. In order to clarify the potential of the PA in more detail, the S-class characteristics at power back-off and with varying oversampling ratio are presented as well.