High efficiency 20–400 MHz PWM converters using air-core inductors and monolithic power stages in a normally-off GaN process

This paper presents high efficiency dc-dc converters based on monolithic normally-off GaN half-bridge power stages with integrated gate drivers. A new gate driver circuitry is introduced, which enhances both the power stage efficiency and the converter overall efficiency. While using only n-type transistors in the GaN process, the proposed gate driver maintains low quiescent power consumption by emulating the complementary operation commonly employed in CMOS processes. Level shifting is accomplished using a bootstrap technique, with the bootstrap capacitor and the bootstrap diode integrated on the same chip. A family of monolithic GaN chips has been designed, targeting operation from up to 45 V, delivering up to 16 W of output power, and operating at 20-400 MHz switching frequencies. The GaN chips are verified in synchronous buck converters, demonstrating record peak power stage efficiencies of 95.0% at 20 MHz, 94.2% at 50 MHz, 93.2% at 100 MHz, 86.5% at 200 MHz, and 72.5% at 400 MHz.