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202 3. Reference Manual
Definition
Definition−>Netlist[† † †]|Circuit[† † †]
define a model in terms of an equivalent Netlist or
Circuit object
Definition−>Equations[† † †]
Format of the Definition argument.
define a behavioral model in terms of a system of
equations
With the Definition argument, you specify the implementation of a model. A model can be
implemented either as an equivalent circuit or as a set of linear or nonlinear differential-algebraic
equations.
You may use a Netlist or a Circuit object to implement an equivalent circuit. The netlist that
represents the equivalent circuit may contain primitive devices as well as further model references.
There is no fixed limit of the subcircuit nesting level.
The following example shows a model implementation for a simple RC tank.
Definition −> Netlist[
{R, {in, out}, R},
{C, {out, ref}, C}
]
A Circuit object may contain local ModelParameters sections as well as local Model definitions.
Local model definitions and parameter sets should have Scope −> Local to prevent interference
with the global subcircuit and parameter databases. Using a Circuit instead of a simple Netlist
feature allows you to define models with instance-specific model parameter sets, i.e. device model
parameters whose values are calculated from model instance parameters.
For example, the following code implements a device-level description of a bipolar differential
pair with emitter degeneration resistors. The model definition contains a local ModelParameters
statement in which the ohmic collector and emitter resistances RC and RE are calculated as functions
of the BJT area factor Area for each instance of the subcircuit DifferentialPair/DeviceLevel.