Output power capability of class-E amplifiers with nonlinear shunt capacitance

The nonlinearity of the shunt capacitance in a HF class-E power amplifier produces a switch peak voltage higher than expected, in particular at frequencies where the shunt capacitance is solely provided by the device parasitic. Peak values have to be accurately estimated in order to avoid device breakdown and to be able to choose a convenient and not too overestimated transistor for the application. Furthermore, the nonlinear behavior modifies the output power capability of a device in class-E operation. When dealing with a lossy nonlinear device, reducing the ON duty cycle of a design bellow 0.5 might help achieving higher frequencies in ideal class-E conditions, whereas increasing it results in higher output power and efficiency. For the first time, an analysis of peak voltage values and output power capability of a class-E amplifier is presented for several duty-cycles and nonlinearity parameters. Experimental results show good agreement with numerical analysis.