High-efficiency doherty amplifier using GaN HEMT class-F cells for WCDMA applications

This paper presents a high-efficiency GaN high electron mobility transistor (HEMT) class-F Doherty amplifier (CFDA) for wide-band code division multiple access (WCDMA) applications. The class-F power amplifiers (PAs) with significant harmonic suppression are used as the carrier and peaking cells. For validations, the class-F PA is designed and implemented with 25-W GaN HEMT at 2.14 GHz. From the measured results for a single tone, the implemented class-F PA shows the peak power-added efficiency (PAE) and drain efficiency of 72.2% and 75.8% with a gain of 13.2 dB at an output power of 43.2 dBm by suppressing harmonic power levels below −55 dBc. For the proposed CFDA, the PAE and drain efficiency of 56.3% and 60.1% is achieved at 39.5 dBm (6-dB back-off power from Psat) for a single tone. For a one-carrier WCDMA signal, the CFDA shows the PAE of 44.9% with an adjacent channel leakage ratio (ACLR) of −22.1 dBc (±2.5 MHz offset) at 36.5 dBm, while an ACLR of −35.4 dBc with the PAE of 39.7% is achieved for the CEDA after linearity optimization.