Band separation in linear-assisted switching power amplifiers for accurate wide-bandwidth envelope tracking

Linear-assisted switching power amplifiers are based on combinations of switching converters (for high efficiency) and linear amplifiers (for high-speed, wide bandwidth responses) in applications such as envelope tracking (ET) for radio-frequency (RF) power amplifiers. This paper presents a pre-filter design approach for band separation of inputs signals for the linear and the switching amplifier stages, respectively, to achieve high-accuracy, wide-bandwidth responses, while minimizing the power processed by the linear amplifier. The approach is verified by experiments on an ET prototype consisting of a GaN-based synchronous buck converter operating at 20 MHz switching frequency at greater than 90% efficiency, and a linear amplifier having greater than 100 MHz bandwidth. Experimental results demonstrate very accurate tracking (less than 3% RMS error) of 10 MHz and 20 MHz envelope signals typical for 4G (LTE) RF transmitters.