Asymmetrical outphasing: Exploiting conjugate continuous modes of operation

In conventional techniques for efficiency enhancement of outphasing systems, identical power amplifiers are employed for each branch while the output combining network is optimised using reactive compensating elements. In this work a methodology is presented for asymmetrical branch amplifier design based on the conjugate load modulation trajectories seen by each PA branch. Closed form equations and simulations are presented, demonstrating that conjugate modes of operation PAs can be used for the upper and lower amplifier branches in outphasing systems to achieve ideal maximum efficiency over the outphasing backoff range. As a proof of concept, Class B and Class J PAs were built using the Cree CGH40010 GaN HEMT. The Class J PA exhibited over 15% improvement in drain efficiency at 4dB back-off compared to the Class B PA when both were measured with the lower branch outphasing load trajectory.