A small-signal high-frequency model for the four-terminal intrinsic MOSFET valid in all regions of operation

This paper presents a four-terminal small-signal high-frequency model, valid in weak moderate and strong inversion regimes, for the intrinsic part of the long-channel MOS transistor. Small-signal partial differential equations describing the "transmission-line" behavior of the MOSFET are derived and solved to arrive at a complete set of admittance parameters. Based on different approximations of these parameters various models are presented, each of different upper frequency limit of validity. By discussion the frequency range of validity of these models, the inadeqacies of the quasi-static models at high-frequencies are highlighted.