A new charge based MOS transistor model for capacitances which will conserve transient charges is introduced. The model is required to accurately simulate a certain class of dynamic circuits. This model features continuous charge formulation in all regions of operation: accumulation, cutoff, and strong inversion. Capacitances are continuous in all regions except on the strong inversion to cutoff border. The channel potential is approximated by novel and weighted functions of the drain and source potentials. A hyperbolic tangent function splits the channel charge in strong inversion between the source and drain. Charge conservation and accuracy of the model are demonstrated with some real examples.

A new circuit simulation model is presented for impact ionization generated MOSFET substrate current. The model uses four parameters to accurately model substrate current over a wide range of device dimensions and operating voltages, including operation in the linear region. The model is able to model substrate currents from both heavily doped and lightly doped devices.