A 2.7-GHz multi-level PWM carrier-bursting RF transmitter

Carrier-bursting is an attractive RF transmitter concept to achieve high efficiency. The power amplifier (PA) itself either operates at its peak efficiency or is turned off. Another efficiency-enhancing approach is the Doherty concept, where the main PA reaches its peak efficiency already in back-off and the peak PA contributes at high input levels to reach the desired output power. In this work, we attempt to combine the best of both concepts and derive a two-level dual-output pulse width modulator driving two PAs whose outputs are combined. We have evaluated the concept by a real-time FPGA implementation of the modulator for a 2.7GHz carrier driving two Class-AB PAs with a combined peak output power of 30W. The approach exhibits a potentially more pronounced back-off efficiency peak compared to the Doherty concept. Furthermore, the overall efficiency scales with the drain efficiency of the PAs and can thus be improved by employing Class-D or Class-F PAs.