Bandwidth and efficiency enhancement schemes in Radio Frequency Power Amplifiers

The increasing demand of high bandwidth for upcoming 5G technologies is challenging the RF power amplifier designers to achieve high efficiency over wide bandwidth. Continuous Class-B/J and continuous Class F power amplifier are good candidates for such wideband applications. However, the design of such power amplifiers require careful selection of design space which can result into realizable solutions in terms of matching network at extrinsic package plane of the device. The model-based non-linear embedding techniques can be used as an efficient tool to optimally select intrinsic loads at current source reference plane which can yield Foster impedances at the device package reference plane after projection with the embedding device model. However, these power amplifiers must be operated at saturation for efficient transmission. In order to handle modern communication signals with high crest factor, the schemes such as load modulation should be used to operate such power amplifiers efficiently even at back-off. Therefore, the schemes such as carrier aggregation, where, overall aggregated bandwidth can be achieved by inter/intra-band concurrent transmission requires multi-band/broad-band power amplification with capability of handling high crest factor signals. This talk discusses the design strategy for continuous Class-J and continuous class-F power amplifiers using non-linear embedding model. The emphasis is given to optimum selection of design space resulting into realizable foster impedance at device package reference plane thereby relaxing the requirements of matching network. These power amplifiers are also used to enhance operating frequency range of Chireix outphasing scheme. In addition, broad-band multi-stage Doherty power amplifier is also discussed as a solution for average efficiency enhancement at higher back off of order 10-12 dB.