Linearity Enhancement of GaN Power Amplifiers Based on Second Harmonic Injection Technique

In this paper, a new approach for improving the linearity characteristics of GaN power amplifiers is presented. The method is based on the injection of the second harmonic signal to the input of the power amplifier through a forward path. The effect of the second harmonic injection on the linearity characteristics of the power amplifier is studied using two-tone theory and simulations. An active three-port linearizing circuit with the ability to generate a second harmonic signal with adjustable amplitude and phase has been proposed to implement this method. Further, the paper method has been evaluated for improving the linearity of two 10-watt power amplifiers with different nonlinear characteristics. As a concept, the proposed circuit is also fabricated and used for linearizing the GaN power amplifier. It has been shown that by injecting the second harmonic signal and properly adjusting its amplitude and phase, in addition to improving the linearity characteristics, including third-order intermodulation (IMD3), adjacent channel power ratio (ACPR), and AM-PM characteristic, the 1-dB compression point is also increased.