Efficiency enhancement of linear GaN RF power amplifiers using the Doherty technique

levels. An amplifier operating at higher back-off however has low energy efficiency. Hence, to meet the stringent linearity requirements and at the same time operating the amplifiers at their highest possible efficiency becomes bottleneck in the basestations. Consequently, thorough analysis of highly linear and efficient amplifiers is highly demanded. Primarily, the selection of a proper semiconductor device technology is a prerequisite for a highly linear and efficient amplifier design. Among others, in this thesis, AlGaN/GaN HEMTs are used for highly linear and efficient amplifier design. For fast and reliable amplifier design, an accurate large-signal model has been derived. The research work demonstrated a linear amplifier design procedure through out-of-band distortion suppression. High efficiency amplifier design technique through harmonic tuning has been also highlighted to achieve a high peak efficiency. To achieve high efficiency up to 8.5 dB back-off the use of efficiency enhancement technique has been considered. Subsequently, improved design procedures of efficiency enhancement techniques based on the Doherty technique has been provided. Most importantly, it is shown that the performance of the realized Doherty amplifiers can fulfill the efficiency requirements of a UMTS basestation.