Fitting of 2-dimensional polynomial device model based on simulated voltage and current spectra

This paper presents a fitting technique for polynomial 2-dimensional nonlinearity, based on voltage current spectra. It will be shown that despite the strongly correlating controlling voltages, the nonlinear 2-dimensional drain-source current (I_DS) of the 30 W RF power transistor model can be fitted. Furthermore, a simplified Volterra presentation of the 3rd order intermodulation distortion (IM3) contributors of I-V and Q-V sources can be constructed. The results match well with the data simulated using harmonic balance. Also IM3 phasors of the input and output of the device are presented. The analysis shows that the total output IM3 current is dominated by the distortion from I_DS. Also a significant portion of the IM3 current is caused by the fact that output IM3 voltage appears across linear but large drain-source capacitance (C_DS).