DARPA's Microscale Power Conversion Program

Starting more than a decade ago, DARPA began funding the materials and device developments of group III-nitride electronics to push toward the limits of cutoff frequency, breakdown voltage, power density and reliability of GaN HEMTs. These transistors have the potential to realize RF power amplifiers with both high output power and power added-efficiency (PAE), compared with those based on other III-V materials (GaAs or InP). Device properties notwithstanding, GaN-based, transmitting high Peak-to-Average Ratio (PAR) RF signals will result in lower PAE when constrained to fixed drain voltage during input back-off. The Microscale Power Conversion (MPC) program seeks to create a very high efficiency RF transmitter as either a monolithic integrated circuit or system-in-package module in which a MMIC power amplifier is integrated (co-designed) with a dynamic voltage power supply and control circuit. The key enabling device technology to be developed for the high-speed power supply modulator is a fast, low-loss GaN power switch. Track 1 of the MPC program seeks to develop packaged, high-speed (>1 GHz), E-mode power switches capable of simultaneously satisfying 50 volt operation, 10 W power handling, Blocking voltage > 200 volts, dynamic on-resistance Ron-dynamic < 1 Ω-mm and output voltage slew rate > 500 V/ns. The final goal of the MPC program (Track 2) is to leverage the power switch developments in Track 1 to realize co-designed RF transmitters. These RF transmitters will operate at X-band frequencies (or higher) while providing 5 W of RF output power at an average composite PAE of 75%, with at least 500 MHz of RF envelope bandwidth.