Output filter design in high-efficiency wide-bandwidth multi-phase buck envelope amplifiers

Supply modulation is a system efficiency improvement technique in radio-frequency (RF) transmitters, where a power converter operating as an envelope tracking (ET) amplifier serves as the power supply for an RF power amplifier. This paper presents design of higher-order output filters in multi-phase buck ET amplifiers to achieve wide-bandwidth tracking with high efficiency using zero-voltage switching (ZVS) technique. The approach is verified by experiments on two-phase GaN-based ET prototypes operating at 10 MHz and 50 MHz per-phase switching frequency, and having fourth-order filters with 5 MHz and 20 MHz tracking bandwidth, respectively. Experimental results demonstrate accurate tracking of 2.4 MHz and 20 MHz bandwidth LTE envelope signals with 93.2% and 89.7% power-stage efficiency, respectively.