RFPA supply modulator using wide-bandwidth linear amplifier with a GaN HEMT output stage

This paper presents an envelope tracking supply modulator for a high efficiency radiofrequency power amplifier (RFPA). A wide bandwidth linear amplifier using a GaN high electron mobility transistor (HEMT) as a source follower output stage is described. A low bandwidth, high efficiency current controlled Buck converter is used to assist the linear amplifier and improve the system efficiency. Steps towards integration of the supply modulator and the RFPA are given through inclusion of the modulator output stage with an RFPA on a microwave monolithic integrated circuit (MMIC). Simulation and experimental results are presented for a 150 MHz bandwidth, 9 V to 27 V output voltage modulator supplying a 10 GHz RFPA.