Application of Load-Pull X-Parameters for GaN Device-Based Load Modulated Balanced Power Amplifier Design

Abstract

In this work, the design of a load modulated balanced power amplifier (LMBA), which composed of a pair of classical balanced power amplifier (BA) and a signal control power amplifier (CA), based on using the X-parameter model is presented for the first time. A 10-W gallium nitride (GaN) packaged transistor is used for the power amplifier (PA) design. The extracted X-parameter model of the device under test (DUT) can accurately predict the nonlinear behavioral of the device, including both fundamental and harmonic characteristics, and determine the region of the Smith chart that leads to the optimal output power and drain efficiency (DE), with which the BA and CA are designed. In order to facilitate the application of the X-parameter for LMBA design, the X-parameter model of the classical BA pair is further extracted. Finally, an LMBA is fabricated and tested to verify the validity of the proposed design methodology. The measurements performed on the developed prototype show a saturation output power of up to 43.2 dBm in the frequency range of 1.3 GHz-1.6 GHz, with a saturation DE over 73% and an output power back-off (OBO) efficiency over 51% when it has more than 9 dB output power back-off. A single-carrier 20-MHz long-term evolution (LTE) signal is used to test the designed PA, and performance of the amplifier both with and without linearization are given.