Optimized coding scheme for class-S amplifiers

This paper is based on a voltage-mode class-S power amplifier for the 450 MHz band using GaN-MMICs. To optimize back-off performance, the conventional topology is modified and the circuit is operated using different coding schemes for the input signal. While for the classical band-pass delta-sigma modulation, a peak output power of 2.3 W with 38% drain efficiency is obtained, tests using a pulse-width modulation approach yield significant improvements, with a maximum output power of 3 W with more than 80% drain efficiency. At 6 dB and 10 dB power back-off, 60% and 40% efficiency are achieved, respectively.