Linearity Characterization of the Self-Enhanced Class J PA Operating Mode through Modulated-Signal Load-Pull Measurements

Recently, single-tone harmonic load-pull measurements provided evidence for the self-enhanced Class J operating mode in RF power transistors. In Class J, the non-linear output capacitance causes the drain-voltage to peak without the phase-shift as is the case with a linear drain-source capacitance, resulting in increased output-power and drain-efficiency. Typically, improvements in the efficiency of RF power transistors tend to compromise linearity and vice versa. In this work we present a methodical way to characterize the linearity-efficiency trade-off of the self-enhanced Class J operating mode through on-wafer modulated-signal harmonic load-pull measurements. Rather than only characterizing the single-ended device in its maximum power and maximum efficiency impedances, extra consideration went into choosing loading impedances that bring the device in a state that is most resemblant of the state of a carrier-device in a Doherty arrangement.