| Parameter Name | Description |
|---|---|
| off | Device is initially nonconducting, for circuit convergence assistance. |
| m=val | Device multiplicity factor. |
| l=val | Channel length in meters. |
| w=val | Channel width in meters. |
| ad=val | Drain diffusion area in square meters. |
| as=val | Source diffusion area in square meters. |
| pd=val | Drain junction perimeter in meters. |
| ps=val | Source junction perimeter in meters. |
| nrd=val | Drain equivalent squares for resistance. |
| nrs=val | Source equivalent squares for resistance. |
| ic=vds,vgs,vbs | The initial voltages (initial condition) for transient analysis. |
| icvds=vds | The initial vds (initial condition) for transient analysis. |
| icvgs=vgs | The initial vgs (initial condition) for transient analysis. |
| icvbs=vbs | The initial vbs (initial condition) for transient analysis. |
| temp=val | Device operating temperature, degrees celsius. |
The parameters listed above are representative of the SPICE3 MOS models, but except for `m' are fairly universal. Some third-party MOS models may have additional nodes and parameters. Consult the model documentation for the full listing.
The nd, ng, ns, and nb are the drain, gate, source, and bulk (substrate) nodes, respectively. The modname is the model name, l and w specify the channel length and width in meters, and ad and as specify the areas of the drain and source diffusions in sq-meters. Note that the suffix `u' specifies microns (1E-6 m) and `p' sq-microns (1E-12 sq-m). If any of l, w, ad, or as are not specified, default values are used. The use of defaults simplifies input file preparation, as well as the editing required if device geometries are to be changed. The pd and ps specify the perimeters of the drain and source junctions in meters, nrd and nrs designate the equivalent number of squares of the drain and source diffusions; these values multiply the sheet resistance rsh specified on the .model line for an accurate representation of the parasitic series drain and source resistance of each transistor. The pd and ps default to 0.0 while nrd and nrs default to 1.0. The parameter off indicates an initial condition of the device for dc analysis. The initial conditions specified using ic or alternatively icvds, icvgs amd icvbs are intended for use with the uic option in transient analysis, when a transient analysis is desired starting from other than the quiescent operating point. operating point. The .ic line provides another way to set initial conditions.
MOS devices using model levels 1-3 accept a real parameter ``m'' which scales all the instance capacitances, areas, and currents by the given factor. This can be used as a short-cut for modeling multiple devices, e.g., m = 2 is equivalent to two identical devices in parallel. This is not available for most of the more complicated and third-party models.