Load Pull Methodology to Characterize Class-E Outphasing Power Amplifiers

A novel load pull methodology to characterize the performance of class-E outphasing power amplifiers is presented. The traditional analysis of the outphasing topology cannot be applied when classE amplifiers are used because these amplifiers do not behave as an ideal current or voltage source. Unlike most other amplifier classes, class-E amplifiers require a phase modulated input signal with constant amplitude. Additionally, class-E amplifiers have non-linear transfer characteristics which are a function of the load impedance. The methodology presented here is based on finding the load locus in the load pull plane of an individual class-E amplifier. Then the performance of the two class-E amplifiers in the outphasing topology is readily obtained. The key advantage of the method is that the load pull characterization of only a single amplifier is required. The methodology is general in that any passive load combining circuit can be used and any amplifier combination can be used in the outphasing topology provided that their load pull data is available. The load locus is derived without any reference to the phase difference between the drive signals.