Simplified Gate Driver Design Technique for Multi-MHz Switching GaN FETs in Three-Level Buck-Based 4G/5G Envelope Tracking

Multi-MHz switching frequency converter-based envelope tracking dc power supplies are widely adopted in modern 4G/5G communication base stations to improve the efficiency of radio frequency power transmitters. The switching loss of buck converter at MHz switching frequency increases with the input dc voltage. To obtain higher output voltage range without much compromise on the efficiency, multilevel converters with discrete low voltage gallium nitride (GaN) field-effect transistors (FETs), switching at multi-MHz frequency, are used. However, the gate driving circuit and PCB layout of a multilevel buck converter are complex and occupy major portion of the board when compared with the power GaN FETs. This article proposes a simplified gate driving technique in a cascaded bootstrapping architecture for a three-level buck converter with reduced number of components that can support up to 40 MHz switching frequency. The converter can reproduce any reference envelope signal with a maximum bandwidth of 8 MHz and output voltage variation from 6 to 42 V. Hardware prototype is developed, and experimental results are presented to validate the concept.