A broadband envelope-tracking push-pull GaN power amplifier using grounded-coplanar ring Marchand balun

This paper presents a broadband (0.5GHz to 2.2GHz) power amplifier with output power up to 25W and drain efficiency up to 69%. Further, its use in an envelope tracking system to achieve high efficiency in backoff over a comparable carrier bandwidth is presented. The RF PA employs a 0.25um (Cree) GaN process in a custom IC design, together with a broadband and low-loss planar Marchand balun implemented in an accompanying PCB. When used together with an envelope amplifier in an envelope tracking system, high efficiency for LTE-modulated signals is demonstrated over 0.8 to 2GHz. At 1GHz, an average output power of 7.2W and 47% efficiency was achieved for a 10MHz LTE signal with 6.5dB PAPR, while the ACLR is -43dBc with a simple AM-AM and AM-PM digital pre-distortion correction.