Load Estimation by Waveform Harmonics in Class-E RF Power Amplifiers

Class-E RF power amplifiers are a class of RF power amplifiers in which very high power efficiencies can be achieved. Under nominal conditions, there is no voltage across and current through the switching component at the same time. In theory, this means that there are no losses in this switching component. One big problem with these Class E power amplifiers is that these are very sensitive to load-mismatch. Because the design includes two resonant tuned tanks, small changes in load impedance can detune the circuit, resulting in load-dependent output power, power efficiency, peak voltages, peak currents and the device operating outside of safe operating area (SOA) causing degradation or failure of components. To overcome these problems a selfhealing technique can be used to readjust the amplifier to the changed load impedance, by adjusting design parameters real-time. To implement this self-healing technique, the impedance of this changed load has to be known. In this Bachelor Assignment a technique of estimating load impedances by analyzing the harmonic content of the voltage at the switching element. Lookup tables are made, noise sensitivity and accuracy are analyzed for a set of harmonics and an estimation of the performance is carried out. A single harmonic parameter does not give enough information to estimate the load accurately, so combinations of two parameters are studied. The body diode in the FET prevents negative voltages across the capacitor and distorts the waveform. This influence is big as the estimation performance reduces drastically, making it very hard to perform load estimation when negative voltages should have appeared. A model for this behavior is made, and the load estimation technique is analyzed with this effect taken into account. This report concludes with a performance estimation of different combinations of harmonic parameters to estimate the load impedance, presen