Linearity-aware design of Doherty power amplifiers

The linearity is a crucial requirement of power amplifiers. At design level, it is typically assessed by means of AM/AM, AM/PM and IMR, which are extracted from 1- and 2-tone characterization. These however are not fully representative of the actual behaviour under modulated signal excitation, for which purpose other system-level metrics such as the NPR have been successfully introduced. In this paper, different linearity estimations are used to compare two GaN-on-Si Doherty MMIC power amplifiers for Ka-band space applications. One of the two amplifiers shows an AM/PM reduction of more than 30% with respect to the other. However, it is observed that this does not always lead to a reduction in NPR. The reasons for this disagreement between metrics are analysed and discussed.