An 80MHz modulation bandwidth high efficiency multi-band envelope-tracking power amplifier using GaN single-phase buck-converter

We report a high efficiency multi-band Envelope-Tracking Power Amplifier (ET-PA) that supports modulation bandwidth up to 80MHz using real-time digital predistortion (RT-DPD). The ET-PA consists of a broadband RF-PA and a singlephase buck-converter. The RF-PA has maximum PAE over 50% from 0.7 to 2.1GHz in CW measurements. The buck-converter operates at 245.76MHz switching frequency, and attains 78% PAE for modulated signals with 6.5dB PAPR. Both RF-PA and buckconverter were fabricated using a GaN HEMT process. The RT-DPD system can generate the input signals for both buck-converter and RF-PA, and capture the output signal for feedback. An FPGA is employed in the RT-DPD system to perform predistortion in a closed-loop fashion. The overall ET-PA achieves total efficiency of 32.1-35.5%, output power of 30-30.7dBm with 30V supply voltage over 0.9-2.15GHz. By using the RT-DPD, ACLR is improved to below -45dBc even under 80MHz modulated LTE signal with 6.5dB PAPR, maintaining high efficiency. To the authors' best knowledge, this is the widest modulation bandwidth yet reported for an efficient and multi-band ET-PA.