Theoretical study of the effects of the parasitic resistances, R/sub D and R/sub s/, on the voltage and current waveform in the transmission line class E PA

This paper presents a theoretical study focus on the impact of the parasitic resistances of a GaAs FET, R. and Rs, on the voltage and current waveform of a transmission line class E PA at microwave frequencies. In order to consider the parasitic resistances, the classical equivalent circuit of a transmission line class E PA was modified. This feature allows us to observe the behavior of the voltage and current waveform of the FET at different frequencies in contrast to the classical equivalent circuit. Therefore is possible to understand better the cause of the low efficiency at microwave frequencies. Extended expressions for the DC-to-AC transfer function (g), output phase current (p) and output load impedance (I#) in function of the parasitic resistances, CDs and the frequency are shown in order to achieve the ideal voltage waveform in the transmission line class E PA at microwave frequency. A theoretical demonstration will show that at microwave frequencies the influence of the parasitic resistances on w cause a decrease in the RF output power therefore the 100% of efficiency cannot be reached agreeing with previous works [3] and [6]. To avoid the influence of RI, and Us at microwave frequencies according with our work the output capacitance of the transistor (Cos) has to he as small as possible