Modelling of 32-APSK Constellation Distortion and EVM in GaN Power Amplifiers From AM/AM and AM/PM Curves

This paper presents a comprehensive memoryless modelling approach to analyse the distortion characteristics of a GaN power amplifier when transmitting 32-APSK digital signals. The analysis is based on the AM/AM and AM/PM characteristics, as well as the Noise Figure (NF) of the amplifier. The simulations conducted in this study yield constellation diagrams of the output signal, and the resulting Error Magnitude Vector (EVM) is calculated to quantify the distortion's impact of source EVM and input drive level. Practical measurements were conducted on a 12Watt GaN power amplifier operating within the frequency range of 20.2 to 21.2 GHz. The actual constellation diagrams and EVM measurements obtained from the experimental setup demonstrated a good agreement with the calculated constellation and EVM of the output. This model thus provides valuable guidance for optimizing the amplifier's operation and enhancing the overall system's performance in practical communication applications.