Class-E tuned amplifiers in power amplitude modulators

A HF power amplifier used in drain amplitude modulator must have a linear static modulation characteristic i.e. linear dependence of amplifier HF output voltage vs. its supply voltage. This condition essential for obtaining low-level envelope distortions is theoretically met by a class-E amplifier. In this paper the influence of non-linear output capacitance of the transistor in the class-E amplifier on its static modulation characteristic is analyzed. Simulations with PSPICE of class-E amplifiers operating at frequencies 0.5 MHz, 5 MHz and 7 MHz have proven that distortions of the amplifier static modulation characteristic caused by non-linear output capacitance of the amplifier transistor are only slight. However, the decrease of power efficiency of the class E amplifier resulting from non-linearity of transistor output capacitance can be significant even by 40%.