A distortion analysis method for FET amplifiers using novel frequency-dependent complex power series model

This paper proposes a new distortion analysis method for frequency-dependent FET amplifiers, which uses a novel Frequency-Dependent Complex Power Series (FDCPS) model. This model consists of a frequency-independent nonlinear amplifier represented by an odd-order complex power series and frequency-dependent input and output filters. The in-band frequency characteristics of the saturation region are represented by the frequency-dependent output filter, while the in-band frequency characteristics of the linear region are represented by the frequency-dependent input and output filters. In this method, the time-domain analysis is carried out to calculate the frequency-independent nonlinear amplifier characteristics, and the frequency-domain analysis is applied to calculate the frequency-dependent input and output filter characteristics. The third-order intermodulation (IM3) calculated by this method for a GaAs MESFET amplifier is in good agreement with the numerical results obtained by the Harmonic Balance (HB) method. Moreover, the IM3 calculated by this method also agrees well with the measured data for an L-band 3-stage GaAs MESFET amplifier. It is shown that this method is effective for calculating frequency-dependent distortion of a nonlinear amplifier with broadband modulation signals.