Estimation of Intermodulation Rejection Value as a Function of Frequency in Power Amplifier Using AM-AM and AM-PM Diagrams Based on Power Series Analysis

Abstract

A method to predict intermodulation (IM) products of two tone test based on Amplitude to amplitude (AM-AM) and amplitude to phase (AM-PM) diagrams of power amplifier is proposed in this paper. An RF power amplifier is mathematically modeled by a power series in order of 13. Coefficients of the transfer function are obtained by odd-order polynomial fitting of the transfer function of the power amplifier that is modeled by power series, with AM-AM and AM-PM diagrams. Because of considering AM-PM distortion, coefficients have become complex. By using this transfer function, analytical expressions of IM products are derived. Frequency effect of IM products are modeled in suggested method to estimate the effects of changing in input frequency on output. With the mean of this factor the model is able to predict IM products of wideband frequency input. Simulated results agree well with the predicted method in comparisons.