Utilization of RF I-V waveform load-pull information to identify the role FET knee profile has on locating the efficiency maxima

Typically performance maxima in terms of output power, efficiency, etc. are determined from analyzing, effectively “data mining”, load-pull measurements. This approach while identifying relevant design information provides no insight into the origin or location of the relevant maxima. However, if during load-pull measurements the RF I-V waveforms are also measured this insight is available. Measured RF I-V waveform load-pull information from a 10×75μm Gallium Arsenide transistor operating in class-B at 8GHz is used to correctly identify the effect of the knee region of the transistor I-V characteristic on power and efficiency. As a consequence the location of the drain efficiency contours on the Smith Chart are explained in terms of V_min and current waveform compression.