CLASS-E TUNED AMPLIFIERS IN POWER AMPLITUDE MODULATORS

A h.f. power amplifier used in drain amplitude modulator must have a linear static modulation characteristic Le. linear dependence of amplifier h.f. 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 0.5MHz, 5MHz and 7MHz 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%.