This paper gives a summarized overview on the progress and achievements on AlGaN/GaN high electron mobility transistors (HEMT)-based power amplifiers (PAs) for mobile radio applications which have been achieved within two national funded German projects during a period of six years. Starting with a first 34 dBm (2.5 W, peak) amplifier in 2003 the impressive progress toward highly efficient S-band mobile radio PAs with up to >50 dBm (100 W) peak output power is described by means of some selected single- and multiband amplifier demonstrators. This progress has been mainly enabled by clear progress on GaN technology, device packaging, and PA design. Targeting at highly efficient single-band amplifier applications, a 2.7 GHz symmetrical Doherty amplifier with up to 45% drain efficiency at close to 45 dBm average output power under single-carrier W-CDMA (Wideband Code Division Multiple Access) operation using digital predistortion can be highlighted. In case of multiband capable amplifiers addressing software-defined radio applications, a class-AB-based demonstrator covering a frequency range from 1.8 to 2.7 GHz was realized. The amplifier showed >30% drain efficiency up to 2.5 GHz as well as up to 40 dBm average output power under single-carrier W-CDMA operation using proprietary digital predistortion. Finally, Alcatel-Lucent's activities on envelope tracking for future efficiency improved GaN-based amplifiers are described.
Boosted Model Tree-Based Behavioral Modeling for Digital Predistortion of RF Power Amplifiers