Precise simulation of non-quasi-static (NQS) characteristics is crucial for the analog application of MOS transistors. This paper presents the small signal admittance model of four-terminal NQS MOS transistors by solving the differential equation derived from the primary principle. The model contains the bulk-charge effect, the mobility reduction, and the velocity saturation. The results are compared with those for the conventional quasi-static model, the BSIM3v3 NQS model, and the 2-D device simulation.

The inclusion of the non-quasi-static effect is crucial in the simulation of the microwave circuits for MOS transistors. This report proposes a simple model which includes this effect in small-signal simulation. The simulated results are consistent with the measured data up to a frequency that is 30 times higher frequency than the cut-off frequency.