High efficiency two-stage GaN power amplifier with improved linearity

In this paper, we propose a systematic approach to designing a highly efficient two-stage power amplifier (PA) with improved linearity. Investigation into the sources of nonlinearity in gallium nitride (GaN) high electron mobility transistors (HEMT) has been essential prior to the development of the two-stage PA design with improved linearity. A prototype was designed and fabricated using 45W and 6W packaged CREE transistors as the main and driver stages respectively. A peak efficiency of about 70% was obtained, using a continuous wave stimulus, over a bandwidth of 200MHz. When driven with a 20MHz WCDMA signal, at 800MHz, an adjacent channel leakage power ratio (ACLR) of 46dBc and an error vector magnitude (EVM) of about 1.5% were recorded at a peak output power of 39dBm without the use of digital pre-distortion (DPD). These results represent an improvement of about 10dB in ACLR and 2% in EVM for the two-stage PA using nonlinear driver as compare to those obtained using a linear driver.