High-Efficiency Amplifiers with Discretely Variable Output Power

"Modern phased-array transmitters employ a separate power-amplifier (PA) module for each antenna element. The transmitted signals have time-varying envelopes and peak amplitudes that vary over a large dynamic range, resulting in inefficient amplificationby the conventional linear PAs that are presently in use. A number of techniques for efficiency improvement have been developed recently, but many are complex and unsuitable for inclusion in low-cost modules for phased arrays. The proposed program willtherefore examine a variety of techniques for improving the efficiency. The program will begin by determining specifications, evaluating RF-power transistors, and comparing power amplifiers. The program will then compare a number of transmitterarchitectures for maintaining high efficiency over a range of output amplitudes. Candidates include continuous envelope tracking, stepped envelope tracking, electronic tuning, outphasing (Chireix), and multiple switched PAs (e.g., Doherty). Theparameters of interest include not only efficiency, bandwidth, and linearity, but also complexity, cost, size, and weight. Finally module approaches will be synthesized and recommended for various frequencies from 1 to 100 GHz. Adaptations of the technology developed in this program will find use in a wide variety of modern RF/wireless systems. Low-power transmitters will find wide use in cellular/PCS handsets, where they will reduce the consumption o