Wideband Class B Power Amplifier Topologies

Abstract

Wireless communication has encountered a tremendous growth over the past few decades. The increased plurality in communication standards, characterized by the use of different operating frequencies and data rates, has translated into very tough specifications for the broadcasting base station power amplifier, in terms of efficiency, bandwidth and linearity. For this reason, currently many high efficiency power amplifier concepts are investigated for their suitability to handle the upcoming generations of wireless communication standards. At this moment the Doherty power amplifier (DPA) is a popular concept, which gives good effciency in the power back-off, making it a suitable choice when dealing with signals that have a high peak-to-average power ratio. To be efficient in power back-off operation, the Doherty power amplifier is composed out of two linear amplifiers with an impedance inverter as an output power combiner. Due to its high complexity, the traditional Doherty amplifier is limited for its RF bandwidth. In view of this, the objective of this thesis is to design a linear wideband class-B power amplifier cell which allows incorporation in the DPA. For this purpose an LDMOS based push-pull topology together with baluns (implemented by bondwires) at the input and output of the transistors has been adapted. The described topology helps to achieve an orthogonal relation between the fundamental path and its second harmonic, resulting in wideband high efficiency operation. The resulting amplifier provides an output power of 60 W with a power added efficiency greater than 48% over a relative bandwidth of 40% centered around 1:8GHz.