Chireix's / LINC Power Amplifier for Base Station Applications Using GaN Devices with Load Compensation

Abstract

New generations wireless communication systems require linear efficient RF power amplifiers for higher data transmission rates. However, conventional RF power amplifiers are normally designed for peak efficiency under maximum output power condition. Consequently, when the power is backed-off from its maximum point, the amplifier efficiency drops sharply. As a result, the mean amplifier efficiency is much lower than the efficiency at peak power level. The Chireix outphasing power amplifier is one of the most promising techniques that can simultaneously provide high efficiency and high linearity. Such approach was the origin of the term LINC (LInear amplification using Nonlinear Components), a technique that allows the power amplifiers to continuously operate at their peak power efficiency while providing an almost undistorted output signal. In this project, a Chireix outphasing amplifier for 2.14 GHz with load compensation has been fabricated using GaN HEMTs delivered by CREE. A considerable efficiency improvement has been achieved. The simulation result shows that the drain efficiency of 74% is obtained at 49 dBm peak output power, and the efficiency is kept above 55% over 10 dB power back-off range. The drain efficiency of 70% is measured at 48.5 dBm output power. To meet an increasing demand for wireless communication terminals to handle multi-band multi-mode operation, multi-band multi-mode power amplifiers are urgently needed. An investigation into how to implement multi-band Chireix's outphasing amplifiers has been carried out. Two proposals for implementing potential dual-band Chireixâs amplifiers have been presented. In addition, a comparison of the efficiency under the condition of static load modulation has been made between GaN HEMT devices and LDMOS devices. The result of the comparison is that GaN HEMT devices conspicuously outperform LDMOS devices in terms of drain efficiency under static load modulation.