This section lists the equation variables and constants.
MOSFET Current Convention, N-channel shows the assumed direction of current flow through a MOS transistor. When printing the drain current, use either I(M1) or I1(M1) syntax. I2 produces the gate current, I3 produces the source current, and I4 produces the substrate current. References to bulk are the same as references to the substrate.
Star-Hspice uses three equivalent circuits in the analysis of MOSFETs: DC, transient, and AC and noise equivalent circuits. The components of these circuits form the basis for all element and model equation discussion. The equivalent circuit for DC sweep is the same as the one used for transient analysis, except capacitances are not included. Figures Equivalent Circuit, MOSFET Transient Analysis through Equivalent Circuit, MOSFET AC Noise Analysis display the MOSFET equivalent circuits.
The fundamental component in the equivalent circuit is the DC drain-to-source current (ids). For the noise and AC analyses, the actual ids current is not used. Instead, the model uses the partial derivatives of ids with respect to the terminal voltages vgs, vds, and vbs. The names for these partial derivatives are:
The ids equation describes the basic DC effects of the MOSFET. The effects of gate capacitance and of source and drain diodes are considered separately from the DC ids equations. In addition, the impact ionization equations are treated separately from the DC ids equation, even though its effects are added to ids.