A High-Efficiency Linear MRI Transmit Amplifier Using Envelope-Tracking

Pascal P. Stang¹, John M. Pauly¹, Greig C. Scott¹

Linear Class-AB RF amplifiers are favored in MRI for their excellent linearity and phase stability. Yet the wide peak-to-average power spread common in MRI transmit pulse sequences forces linear amplifiers to run at dismal efficiencies, producing high levels of pulsatile heat dissipation which negatively impacts design, performance, and operating consistency (e.g. memory effects). We apply envelope-tracking to classic linear amplifiers to achieve higher efficiency and reduced thermal stress without sacrificing performance or fidelity. Comparative results are presented on sinc and hard pulses at a range of amplitudes. Broad DC-to-RF efficiency improvements up to 3.5x are observed, translating into reductions up to 40% in dissipated power while delivering the same RF output.