AM/AM and AM/PM Distortion Generation Mechanisms in Si LDMOS and GaN HEMT Based RF Power Amplifiers

This paper provides a comprehensive analysis of the AM/AM and AM/PM nonlinear distortion generation mechanisms arising in the most common RF power amplifier (PA) technologies presently used in cellular infrastructures: the Si LDMOS and the GaN HEMT. Considering all the known nonlinear elements of both transistors' equivalent circuits, namely, the drain-source current and the gate-source, the gate-drain and the drain-source capacitances, semi-analytical expressions are derived for the PA's AM/AM and the AM/PM distortions. This model is shown to offer an accurate nonlinear distortion prediction across the whole range of operation classes (Class C, Class B, and Class AB) and signal ranges (from small-signal to power saturation), and a qualitative view of the physical distortion generation mechanisms, which is useful for nonlinear circuit design and performance optimization.