The general form of the instance of a MOSFET is the following:

M<name> <nodeD> <nodeG> <nodeS> <nodeB> <model name> [L=<value>] [W=<value>] [AD=<value>] [AS=<value>] [PD=<value>] [PS=<value>] [NRD=<value>] [NRS=<value>] [M=<value>] [OFF] [IC=<VDS0,VGS0,VBS0>] [TEMP=<device temperature>]



Is the name of the component and the initial letter M identifies the MOSFETs.

nodeD, nodeG, nodeS, nodeB

Are the drain, gate, source, and bulk (substrate) nodes, respectively.

model name

Is the model name.

L, W

L and W are the channel length and width, in meters. If any of L or W are not specified, default values (DEFL and DEFW) are used.


AD and AS are the areas of the drain and source diffusions, in meter2. If any of AD, or AS are not specified, default values (DEFAD and DEFAS) are used.


PD and PS are the perimeters of the drain and source junctions, in meters. PD and PS default to 0.0.


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 control line for an accurate representation of the parasitic series drain and source resistance of each transistor. NRD and NRS default to 1.0


A parallel device multiplier (default = 1), which simulates the effect of multiple devices in parallel. Level 1,2,3 only.


OFF indicates an (optional) initial condition on the device for the dc analysis.


The (optional) initial condition specification using IC=VDS, VGS, VBS is intended for use with the UIC option on the .TRAN control line, when a transient analysis is desired starting from other than the quiescent operating point. See the .IC control line for a better and more convenient way to specify transient initial conditions.


The (optional) TEMP value is the temperature at which this device is to operate. This value, if specified, takes precedence over the analysis temperature.


Two different forms of initial conditions may be specified for some devices.

The first form is included to improve the dc convergence for circuits that contain more than one stable state. If a device is specified OFF, the dc operating point is determined with the terminal voltages for that device set to zero. After convergence is obtained, the program continues to iterate to obtain the exact value for the terminal voltages. If a circuit has more than one dc stable state, the OFF option can be used to force the solution to correspond to a desired state. If a device is specified OFF when in reality the device is conducting, the program still obtains the correct solution (assuming the solutions converge) but more iterations are required since the program must independently converge to two separate solutions. The .NODESET control line serves a similar purpose as the OFF option. The .NODESET option is easier to apply and is the preferred means to aid convergence.

The second form of initial conditions are specified for use with the transient analysis. These are true 'initial conditions' as opposed to the convergence aids above. See the description of the .IC control line and the .TRAN control line for a detailed explanation of initial conditions.


M1 2 1 0 0 MMOD L=10u W=20u

See also

MOSFET Instance Parameters