Inphasing Signal Component Separation for an X-Band Outphasing Power Amplifier

Abstract

This work investigates signal component separator design for an RF-input outphasing power amplifier (RFIO PA). In the RFIO architecture, the phase- and amplitude-modulated input signals to the outphasing power stage are realized using a nonlinear “inphasing” network, resulting in an outphasing system that operates on a single RF input. Previous RFIO work has demonstrated the feasibility of this approach, but the combined nonlinear effects of the inphasing and outphasing networks have resulted in overall poor linearity. In this work, we use a simplified transistor model to predict the inphasing network design requirements, and then compare three nonlinear components to synthesize the required transfer function. An $X$ -band monolithic microwave-integrated circuit (MMIC) in 150-nm GaN is used as the output stage, and its operation is characterized for hybrid inphasing networks based on three different technologies: diode-connected HEMT, p-i-n diode, and nonlinear GaN mesa resistor. The RFIO PA with mesa resistor inphasing network achieves a linearity-efficiency compromise with −27.9 dBc adjacent channel leakage ratio (ACLR) and 29% PAE at an average output power of 27.7 dBm for a 100-MHz long-term evolution (LTE) signal with 7.9 dB peak-to-average power ratio (PAPR) centered at 10 GHz.