On the Efficiency of Output-Matched Radiofrequency Power Amplifiers

The efficiency of a radiofrequency power amplifier is analyzed at large-signal under the constraint of conjugate output matching. The result is that, while in low-efficiency regimes, like class-A, the output matching leads to a decrease of the efficiency by a factor 2 (in agreement with the literature), in class-AB and beyond, the efficiency penalty is smaller. As a consequence, it is possible to design a matched PA with efficiencies comparable to those of an unmatched PA by appropriately adjusting the drive level. The results of the presented analysis are validated by means of transistor-level simulations.