Comparison of Class C and High Efficiency Class E Amplifiers at 435 MHz

This article deals with the comparison of class C and class E amplifiers designed with an identical transistor, substrate, and frequency. Both types of amplifiers have a theoretical efficiency of 100 %; however, more attention is paid to class E amplifier, because of its complexity and difficulty of design. The efficiency of both classes reached over 75 %. The working frequency of designed amplifiers was 435 MHz using lumped components. The topology of the class C amplifier is typical with input and output filter matching at the fundamental frequency, and the design of the class E amplifier is with shunt capacitance complemented with series resonant circuit fundamentally tuned. Class E amplifier with a shunt capacitance designed with E-pHEMT transistor is unique, because of small drain voltage which has a distinct influence on switching capacitor value which resulted in hundredths to units of picofarads. The amplifiers were simulated, manufactured and measured results were compared. The class E amplifier is therefore presented at such frequency where transmission lines cannot be used because of their length and even the lumped resonators tuned to higher harmonics frequency start to be undesignable.