High Frequency Multiphase Flying Capacitor Multilevel Envelope Tracker with Coupled Inductor

Abstract

Envelope tracking power supplies for RF power amplifiers greatly improve amplifier efficiency. A system with high dynamic bandwidth can track envelopes at higher frequency. Buck converter system bandwidth improves as converter size decreases, but smaller converter size increases peak current stress and losses. Flying capacitor multilevel (FCML) buck converters effectively multiply the converter frequency, reducing non-idealities and allowing smaller converter size and improved bandwidth. Coupling the inductors of multiple phases can offer additional improvements in flying capacitor voltage balance and inductor current ripple, reducing switch stress and allowing for even smaller converter size. This thesis presents analysis, simulation, and prototyping of a three-level, two-phase buck converter and compares performance with and without coupling the inductors of the two phases. Simulation shows that the coupled inductor substantially improves flying capacitor voltage balance and inductor current ripple. Experimental verification with a prototype realizes the improvement in voltage balance, and shows some reduction in inductor current ripple. These improvements allow the FCML converter to operate at higher frequencies with higher control bandwidth and better balancing for envelope tracking applications.