The effect of transistor feedback capacitance in class-E power amplifiers

In this brief, the contribution of transistor feedback capacitance to the total output capacitance in Class-E power amplifiers is analyzed. It is shown that the feedback capacitance loads the output of the transistor by its nominal value plus an amount proportional to the ratio of the input voltage amplitude to the peak voltage across the output of the transistor. Because a high-input drive is required for good transistor switching action, high-voltage swings may be present at the input, and so this effect should not be neglected. Computer simulations are used to verify the validity of this analysis by comparing the cases without feedback capacitance, with feedback capacitance, and where the effect of the feedback capacitance is accounted for using the design equation derived in this report.