De-mystifying AM-PM characteristics through the definition of the complex Transducer Gain ĜT

Load-pull is a well-established measurement and simulation technique to characterize radio-frequency power transistors. The component-level information it provides is used to predict how the transistor will behave at system level. With the eye on linearity, the amplitude-and phase-modulation characteristics (AMAM-and AMPM-characteristics) are the most important metrics considered. This paper highlights a couple of pitfalls in the translation of the component-level characteristics to the system-level and how to circumvent them. It is explained how AMAM and AMPM characteristics depend on the fundamental source-impedance, but also how the precise knowledge of this source-impedance is irrelevant during the load-pull experiment itself, since its influence can be added in post-processing without loss of generality.