Study of the GaN HEMT Doherty Power Amplifier distortion

The Doherty architecture is presented as an ideally linear efficiency enhancement technique. The theory behind this statement assumes that the output of the Carrier and Peaking Power Amplifiers (PAs) are ideal current sources, which is far from the truth in practical implementations. Both the Carrier and Peaking PAs are composed of nonlinear current sources suffering from both AM/AM and AM/PM distortion. Furthermore, the AM/AM and AM/PM characteristics of the Carrier and Peaking PAs, when operating in a Doherty arrangement, are very different from the ones expected from their single-ended operation, especially in GaN HEMT based Doherty PAs. This is exactly the topic addressed by this paper.