A highly linearized second harmonic injected GaN power amplifier

Abstract

This article presents an active second harmonic injection technique for linearizing power amplifiers (PAs). In this method, a second harmonic signal with adjustable amplitude and phase, which is generated by a differential pair network, is injected into the input of a PA in a forward path. The tunable input and output matching circuits of the proposed second harmonic generator provide linearization capability in a wide frequency band. To validate the concept, the proposed second harmonic injection technique was implemented to linearize a GaN PA working around 1.5 GHz. It was shown that applying the proposed linearization method increases the output 1-dB compression point from 33.5 dBm to 39.5 dBm (about 2 dB lower than saturation power) under the CW signal. Furthermore, the backed-off efficiency at a higher adjacent channel power ratio was improved, and improvement of 16 dB at 200 MHz frequency bandwidth was achieved for an 8 MS/s 64-quadraticamplitude modulation signal.