An evaluation of static single-tone X-parameter models in time-varying envelope domain simulations of intermodulation distortion performance

Single-tone X-parameters-based models are time-invariant non-linear mappings, where the output is a multi-harmonic vector mapping of the incident and scattered waves under periodic steady-state conditions. An envelope simulation combines aspects of both the frequency and time domains, where the input waveforms may be represented as discrete carriers in the frequency domain and the modulation envelopes as time-variant waveforms. X-parameter models are evaluated for their swept frequency and power intermodulation distortion (IMD) and the corresponding output third-order intercept point (OIP3) simulation accuracy. Model performance for an example surface mount amplifier is evaluated for both the cases of extrapolated power levels and those where the power level lies within the model boundaries. It is shown that a single-tone static X-parameter model is capable of predicting the swept IMD performance of the device given reasonable power limit model boundaries and a DUT subject to negligible device memory effects.