Analysis and optimization of asymmetric sequential power amplifier

In this paper, performance analysis and optimization of asymmetrical Sequential Power Amplifier (SPA) is presented. From design equations of SPAs, optimized solution is analytically found for the best efficiency, which has not been suggested so far. In addition, throughout the search on coupling ratio, threshold voltage, and output power rating ratio, combinations of parameters for better efficiency are numerically found. The result shows that the overall efficiency is more sensitive to the threshold voltage than to the coupling variation, and that the output-power-rating ratio between the main and peaking amplifiers dominantly determines the efficiency at the peak power level. For the verification, two class-F power amplifiers are designed and used to implement 24dBm power amplifier at 2.35GHz for m-WiMAX application. Measurement result showed 75% of efficiency at the peak power and above 70% with 8dB dynamic range in the optimized condition.