Class-E RF power amplifiers have become quite fashionable in ham radio in the last decade or two.
One of, if not the main contribution to efficiency in a Class-E RF amplifier is the operation of the active device in switching mode where it is either not conducting, or conducting hard (saturated, with very little voltage across it). Both of these are very low dissipation conditions, but in the transition between these states there is significant current and voltage present, the product of which gives significant instantaneous power… so the idea is to make this transition very fast so that the average power is low.
This article discusses effect of slowed switching times on PA efficiency.
Above is a circuit above is from (Sokal 2001) which explains the amplifier and gives guidance on selection of components. Continue reading Switching times in Class-E RF power amplifiers