Linearization of power amplifiers modelling and simulations

Abstract

Due to their good spectral efficiency, linear modulation methods are well suited to digital mobile radio systems. However their envelope fluctuations result, after nonlinear amplification, in out-of-band emissions thus adjacent channel interferences. A solution is to linearize the power amplifier. We present an analog linearization loop based an an improved cartesian feedback method. Its performance is at least as good as those of designs of similar complexity and it offers a great robustness against variation of components characteristics encountered in large volume production. This paper also presents details on a nonlinear amplifier model which was essential for this study. Both AM-AM and AM-PM characteristics are considered. Tests conducted on hardware confirmed the validity of this modelling. A simulation was built to determine the spurious power seen by a receiver tuned to an adjacent channel.