The Large World of FET Small-Signal Equivalent Circuits (Invited Paper)

The small-signal equivalent circuit modeling of microwave field-effect transistors (FETs) is an evergreen and ever flourishing research field that has to be up-to-date with technological developments. Hence, modeling techniques must be continuously adapted and extended to suit best evolving technologies. The extraction of a FET high-frequency small-signal equivalent circuit is a very active and broad research area of significant interest, owing to its use as a prerequisite for noise and large-signal modeling. The aim of this invited article is to provide in-depth knowledge, critical understanding, and new insights into how to extract a FET small-signal equivalent circuit from both theoretical and practical perspectives. To illustrate potential solutions to the key challenges faced by researchers, experimental results for different semiconductor technologies are reported and discussed. The study is focused on the hot research topic of the cold approach that has been, and still is, the most widely used technique for extracting FET small-signal models and on the active role of the transconductance for successful modeling.