GaN-HEMTs as switches for high-power wideband supply modulators

A highly efficient GaN-HEMT based supply modulator suitable for envelope tracking (ET) systems is designed and analyzed. Varying the transistor size in the power switching stage reveals the critical parameters and bottlenecks. The buck-converter power stage is operated at 28 V supply voltage and delivers up to 50 W output power at more than 90% efficiency over 6 dB back-off at 1 MHz switching frequency. So far, switching speeds up to 5 MHz can be accomodated. At present the bandwidth is limited by the gate driver. Simulations show that the GaN-HEMT technology should work well up to 100 MHz switching frequency.