Impact of trapping effects on GaN HEMT based Doherty PA load-pull ratios

This paper presents an explanation for the higher efficiencies commonly obtained from GaN HEMT based Doherty power amplifiers (PAs), when subjected to wider load-pull ratios as compared with their Si LDMOS counterparts, the two main players in base-station PA technology. The analysis starts with the recently derived theory of efficiency dependence on load impedance and quiescent current, to then relate them to the self-biasing effects introduced by GaN HEMT charge trapping phenomena. For validation purposes, measured load-pull ratios of two 15W Si LDMOS and GaN HEMTs transistors are used.