A Comprehensive Analysis of AM–AM and AM–PM Conversion in an LDMOS RF Power Amplifier

In this paper, a Volterra analysis built on top of a normal harmonic balance simulation is used for a comprehensive analysis of the causes of AM–PM distortion in a LDMOS RF power amplifier (PA). The analysis shows that any nonlinear capacitors cause AM–PM. In addition, varying terminal impedances may pull the matching impedances and cause phase shift. The AM–PM is also affected by the distortion that is mixed down from the second harmonic. As a sample circuit, an internally matched 30-W LDMOS RF PA is used and the results are compared to measured AM–AM, AM–PM and large-signal $S11$.