Monolithic multilevel GaN converter for envelope tracking in RF power amplifiers

This paper presents a monolithic multilevel converter realized in a depletion-mode GaN process and intended to operate as a drain supply modulator (DSM) for high efficiency radio-frequency (RF) power amplifiers (PAs). The custom prototype chip includes a four-level power stage with on-chip integrated gate drivers and damping networks designed to mitigate effects of parasitics during output voltage level transitions. An optimization algorithm is described to maximize the drain supply system efficiency using the level voltages and a minimum switching interval as optimization variables. The monolithic multilevel chip is used to construct a four-level converter prototype. Experimental results are presented for tracking 8 MHz sine-wave and 10 MHz LTE envelope signals. The converter output voltage exhibits fast and well damped level-to-level transients. For the 10 MHz LTE envelope signal, the converter achieves greater than 97.3% power stage efficiency at 3.5 W average output power level.