Investigation of the AM/pm distortion in Doherty Power Amplifiers

In this paper, a theoretical investigation of the causes of the AM/PM distortion in Doherty Power Amplifiers is presented for the first time. The distortion sources are identified and a solution to mitigate the AM/PM conversion through the input termination of the Carrier amplifier is also highlighted. The relevant analysis is carried out using a simplified model of the active device and validated by means of full nonlinear model of a commercial GaN HEMT transistor. The role of the Miller effect in such a kind of distortion is stressed, demonstrating the existing link between output load modulation and phase distortion.