Study of parasitic and stray components induced ringings in class E power amplifiers in MHz range

For class E power amplifier circuits operating at switching frequencies of the MHz range or higher, the parasitic capacitance of the MOS transistor switch becomes a significant part of the circuit adding to the usual intended circuit components. For the class E power amplifier, this is often regarded as an advantage because the parasitic capacitor can be utilized for achieving zero voltage and current switchings, thus reducing the size of an external capacitor which has to be inserted. However, parallel connection of parasitic, stray and external capacitors may give rise to high-frequency ringings of the voltage across the switch, causing the circuit to deviate from the desired class E operation. In this paper, the phenomenon and its underlying cause is studied by simulations and experiments. A circuit model of the amplifier with parasitic or stray components is developed to explain the phenomenon.