Modeling of Input Nonlinearity and Waveform Engineered High-Efficiency Class-F Power Amplifiers

A comprehensive time-domain modeling and a generalized design methodology for input and output waveform engineered Class-F power amplifiers (PAs) are presented in this article. A closed-form relationship between input nonlinearity and second harmonic source impedance (Z
_2S
) termination is presented from which efficiency and output power performance are predicted for Class-F PAs. The maximum, minimum, and safe Z
_2S
design space for a Class-F PA are identified. Moreover, the derived design equations show that the typical fundamental load of a Class-F PA operation must be re-engineered in the presence of input nonlinearity in order to achieve optimum efficiency performance. The theoretical analyses are first validated with pulsed vector load-pull (VLP) measurements with a gallium nitride (GaN) 2 mm device. Then, high-power (210 W) GaN 24-mm devices with in-package Z
_2S
terminations are implemented. Measurement results with the new source and load design space show efficiency improvement of 4.4% compared to the nominal Class-F PA.