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3.2 Subcircuit and Device Model Definition 199
Parameters −> {IS, N, BF, BR, Global[TEMP]},
Defaults −> {IS −> 1.*^−16, N −> 1., BF −> 100.,
BR −> 1., TEMP −> 300.15},
you can instantiate a default BJT device without having to specify values for the parameters in the
model reference:
{QDEF, {nout −> C, 2 −> B, 3 −> E}, Model −> BJT, Selector −> DC}
During subcircuit expansion the numerical default values specified by the Defaults argument are
used as model parameter values. The above model reference is thus processed as if its value field
had been specified as shown below.
{QDEF, {nout −> C, 2 −> B, 3 −> E}, Model −> BJT, Selector −> DC,
IS −> 1.*^−16, N −> 1., BF −> 100., BR −> 1., TEMP −> 300.15}
Translation
Translation−>{param
−>expr
, param
−>expr
, † † † }
specify model parameter translation rules
Format of the Translation argument.
The optional argument Translation allows you to specify conversion rules for calculating values of
internal model parameters from external parameters declared with the Parameters argument.
For example, the following code defines a simple BJT small-signal model with the external parameters
RB (base resistance) and
beta (current gain). Internally, the model is implemented using a VCCS whose transconductance gm
is calculated automatically from RB and beta by means of the Translation rule gm −> RB*beta.
Model[
Name −> "BJT", Selector −> "SimpleACgm",
Ports −> {"C", "B", "E"},
Parameters −> {RB, beta},
Translation −> {gm −> RB*beta},
Definition −> Netlist[
{"RB", {"B", "E"}, RB},
{"VC", {"B", "E", "C", "E"}, gm}
]
]
Translation rules may also be specified using the RuleDelayed operator (:>). This enables you
to defer the evaluation of function calls on the right-hand sides of translation rules until model
expansion. In the following list of rules, the thermal voltage Vt of a semiconductor device is