Using a C++ based simulation framework and automatic differentiation techniques for advanced non-linear modelling of microwave active devices

In this paper we describe the use of a novel, flexible, and highly modular simulation environment called Sframe, for microwave device modelling and circuit simulation. The software architecture of Sframe [1, 2], is based on object orientation, automatic differentiation, and wide use of packaged numerical software. The use of automatic differentiation techniques in Sframe greatly simplifies device modelling: it leads to very compact model codes, simplifies the implementation process and eliminates many common sources of error. The same model code is suitable for all analyses of interest such as: DC, linear small-signal, non linear time domain, and harmonic balance. The paper presents tests with the implementation of an advanced non-linear GaAs FET model in Sframe. This equivalent circuit based model [5, 6], introduces novel solutions with respect to the modelling of the non-linear gate charge and drain current, as well as the AC dispersion of transconductance and output conductance. DC, small-signal AC, and single-tone large-signal simulation tests have been successfully carried out and the results are compared with experimental data, for the case of a 0.5 × 300¿m GaAs MESFET. The large-signal tests are done using a novel implementation of the harmonic balance algorithm [4] which is briefly described in the paper.