Behavioral modeling of RF power amplifiers considering IMD and spectral regrowth asymmetries

This paper proposes a new behavioral model to treat asymmetries between lower and upper intermodulation products and spectral regrowth in nonlinear power amplifiers (PAs). Asymmetric intermodulation distortion (IMD) phenomena has been attributed to long time constant envelope memory effects within the PA, and is known to be a limiting factor in predistortion linearization systems. The model developed in this paper is based on the previously developed memory polynomial model. The contribution made in this paper was to augment the memory polynomial model to include a weighted delay tap function that significantly reduces the parameter space required for accurate model identification. Using measured IMD from a 2.1 GHz 170 W PEP LDMOS PA, the coefficients of the 100 tap memory polynomial were extracted. The model is validated by comparing the measured and predicted results when the PA is excited by a two-tone signal with tone spacing extending from 10kHz to 5MHz. The proposed model reduces rms error up to 36% when compared to a conventional unit sample delay memory polynomial model.