The use of automatic differentiation in advanced non-linear modelling of microwave active devices

We describe the use of a novel, flexible and highly modular simulation environment called Sframe, in microwave device modelling and circuit simulation. The software architecture of Sframe is based on object orientation, automatic differentiation and the use of off-the-shelf numerical codes. We present the first tests with the implementation of an advanced nonlinear GaAs FET model in Sframe. This general purpose model, introduces novel solutions, particularly with respect to the modelling of the gate charge, gate capacitances and the RF dispersion of the transconductance and output conductance. The use of automatic differentiation techniques and the modularity of Sframe, lead to very compact model codes, simplifies the implementation process and eliminates many common sources of error. DC and small-signal AC simulation tests have been successfully carried out and the results are shown for the case of a 0.5 μm GaAs MESFET