Analysis of Class-F Power Amplifiers With a Second-Harmonic Input Voltage Manipulation

In this brief, analysis of class-F high-efficiency power amplifiers (PAs) when adding a second-harmonic input voltage to the gate node of the transistor is derived. The theoretical formulations of the drain current, output power, and drain efficiency are elaborated for this case. Based on them, the maximum output power and drain efficiency can be obtained from the closed-form solution set of the initial amplitude and phase of second-harmonic input voltage component. Calculations show that, with a proper second harmonic voltage adding to the input of the transistor, the performance of class-F PAs can be improved evidently. Besides, to validate the theoretical analysis, a simulation using a real GaN transistor has been presented. The relative errors of drain efficiency and output power between the results of theory and simulation are only 1.3% and 2.4%, respectively. To the best knowledge of the author, this is the first full theory to illustrate the performance enhancement of class-F PAs with a second-harmonic input voltage manipulation.