Experimental time-domain evaluation and simulation of high power GaN HEMTS for RF Doherty Amplifier design

This paper presents an automatized, on-wafer time-domain active load-pull set-up developed for a Doherty-oriented characterization of High Power GaN High-Electron Mobility Transistors (HEMTs). From the on-wafer measured Time-Domain Waveforms (TDW) acquisition, all data required for the design of a Doherty Power Amplifier (DPA) are then directly extracted. With this measurement process, designers have then the direct knowledge of the optimal characteristics of high power transistors along the Output Back-Off (OBO). They also can deduce the maximum obtainable operating bandwidth of the final Doherty PA. Simultaneously to this measurement process, simulations based on the use of non-linear foundry electro-thermal model have also been performed to prove the validity of the method to predict Power Added Efficiency (PAE) performances versus OBO. Measurement and simulations have been applied to an 8x125 mu m AlGaN/GaN GH25 transistor from UMS foundry.