Review of Recent Trends on Power Amplifier Design for Modern Communication Systems

Next-generation wireless communication standard 5G requires power amplifiers capable of maintaining high efficiency in the presence of modulated signals with high Peak-to-Average Power Ratio (PAPR) in order to avoid signal clipping and distortion. Meanwhile, a wideband or multi-band capability is necessary for multi-standard applications. In this paper, a brief review of the most recent wideband and high-efficiency power amplifier designs was presented, with a particular focus on Doherty Power Amplifier (DPA) as the most suitable technique. A comparison between different efficiency enhancement techniques was discussed in detail, while the basic concept and principle of operation for the DPA were presented accordingly. Moreover, many innovative designs to enhance the power amplifier's performance in terms of the back-off efficiency and bandwidth extension were discussed. The first topic considered was efficiency enhancement, whereby different solutions such as multi-stage DPA, asymmetrical devices, and output combiner optimization were presented. Meanwhile, another significant topic discussed was bandwidth extension in which a large number of papers was discussed accordingly. Besides, the most important factors of DPA designs limiting the efficiency enhancement and bandwidth extension were highlighted. Most of the presented designs focused on a single approach, either efficiency enhancement or bandwidth extension. Therefore, symmetrical DPA based on the asymmetrical matching network in combination with multi-section impedance matching can be suggested to solve the problem of efficiency degradation at a Back-Off (BO) region. This will extend the bandwidth simultaneously in order to meet the requirements of modern wireless communication systems.