A Hybrid Coupler Based Load-Modulated Digital Power Amplifier

A digital power amplifier (DPA) is proposed based on three switching amplifiers which are enabled and disabled by digital signals to recreate the envelope amplitude of a modulated signal. Each amplifier is optimized for a different peak output power (P
_OUT
) and are connected at their outputs with a transmission line (TL) non-isolated combiner so that they load-modulate one another. The combiner is inspired by the hybrid coupler and optimized with a genetic algorithm (GA) to achieve seven unique P
_OUT
on-states. Under static circuit simulations a 500 MHz prototype achieved a peak P
_OUT
of 29.6 dBm (0.9 W) with an average efficiency of 50.5% over all on-states. The practical DPA achieved an average efficiency of 41.3% over all on-states with a peak P
_OUT
of 30.3 dBm (1.0 W).