Generalized semi-analytical design methodology of class-E outphasing power amplifier

This paper presents a time domain generalized semi-analytical solution for the class-E outphasing power amplifier (OPA). Instead of assuming ideal voltage sources for active devices, the proposed class-E OPA model obtains the circuit elements by analytically solving the class-E equations for two mutually loaded active devices and numerical optimization. The analysis takes into account the dc-feed inductor, duty-cycle, switch resistances and the class-E conditions at certain outphasing angle. Three different topologies are deduced from the proposed generalized model. The design equations for the circuit elements are derived analytically using the given class-E conditions. The overall outphasing performance is obtained numerically, and the optimum design settings are determined by the desired output power and efficiency characteristics. It will be shown that the proposed class-E OPAs can ideally maintain high efficiency (> 80%) at 12-dB power back-off with a static square-wave drive signal. With 5-MHz UMTS downlink signal, the ideal average efficiency is more than 80%. The spectral and modulation requirements are satisfied when the predistortion is applied to the class-E OPA.