Distributed switch FET model that predicts better insertion loss and harmonics

With increasing scale/complexity in phemt switch circuits and dimension shrinking of unit phemt switch devices, distributed effects are becoming crucial on insertion loss and harmonics, especially the second harmonic. Distributed effects of metal resistances and inductances are taken into account in this paper. It is shown that distributed effects, either along the drain/source fingers or along the lateral direction where the signal are fed on the line ends, show impact on frequency roll-off in insertion loss. The parasitic distributed effects especially those of gate fingers beyond the active region, on the other hand, have crucial impact on second harmonics. The new model is analytic and do not need any EM simulator to address layout effects, and therefore is easy to incorporate into large-signal model. The model was validated against various layout and structures in terms of frequency roll-off in insertion loss and the harmonic simulation for a real switch circuit. Through simulation using the new model, it is shown that more design guide rules in layout, as regarding to how to reduce insertion loss and improve 2nd harmonics, are necessary in switch circuit design.