Non-linear measurement data has been exploited in various ways to create behavioral models for high frequency components. Formulations of these models have been defined in terms of traveling waves, with a desire to represent nonlinear behavior of high frequency transistors through a direct extension from linear s-parameters.
The Mesuro model portfolio is comprised of two models – each targeted at a particular end use – Cardiff Model Lite (CML), where the desired output is a local model, and Cardiff Model+ (CM+), which incorporates higher order mixing terms allowing a single model to fit over a range of impedance space.
The Cardiff Model+ formulation has a number of unique benefits over alternative approaches where formulations are truncated. Once the formulation is extended, the model moves away from a local model, where multiple models are required to define an impedance space (i.e load lookup), to a model that has a set of coefficients that describes the behavior of a device over an entire impedance space. This dramatically reduces file size and also allows any interpolation to be defined by the model itself rather than relying upon the interpolation algorithm in the simulator. Also, as harmonic superposition is not assumed in the CM+ formulation, a full harmonic mixing model is uncovered describing harmonic interactions and improving model accuracy particularly for complex modes of operation.
An example setup is shown below, the Mesuro phase reference and modeling framework is compatible with all major VNA’s.