Linearity and efficiency of outphasing microwave amplifiers

RF power amplifiers (PA) are among the key building blocks for wireless communication systems. Current digital communication standards need both high linearity and power efficiency. Generally, there is a conflict between the linearity and efficiency of power amplifiers. The Chireix's outphasing power amplifier is one of the promising techniques that can be used as a linearization and efficiency enhancement technique.; The key advantage of outphasing system is the ability to maintain high efficiency by reducing DC current when output power is decreasing. This requires the use of a 3-port, non-isolating combiner which introduces significant interaction between amplifiers. The objective of this work is to analyze the interaction between the two amplifiers in an outphasing system and show the potential of its application in modern communication system.; The analysis of the lossless non-isolating combiner indicates that the nature of the interaction is indeed an active load pull. The voltage combiner forces the two amplifiers share the same output current which is on the other hand decided by the output voltages of both the amplifiers. The non-isolating combiner requires power amplifiers that resemble ideal voltage sources, whose output voltage is independent of output current, to work properly in an outphasing system. This work shows that reasonably good efficiency with low distortion can be obtained by selecting the right type of amplifiers. A new approach to analyze the behavior of power amplifiers in outphasing system is introduced. Using this approach the amplifier output current - voltage relationship can be used to predict how well a particular type of amplifier will perform in this configuration. Analysis and comparison between different types of power amplifiers is presented.