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3.2 Subcircuit and Device Model Definition 197
By declaring a port as Optional, you can tell Analog Insydes to ignore any missing connections to
this port and perform some default action instead, such as connecting the port to the ground node.
This is useful for modeling integrated semiconductor devices with substrate pins. If the substrate
pin of a BJT or MOSFET model is an optional port, you can use the same model definition for
both three-pin and four-pin devices. If you write the Ports specifications for these device types as
shown below, then the substrate pin is connected implicitly to the ground node and source terminal,
respectively, whenever a BJT or MOSFET model is instantiated as a three-pin device.
The following Ports declaration causes the substrate pin S of a BJT device to be connected to the
ground node if S is left unconnected:
Ports −> {"C", "B", "E", Optional["S", 0]}
This causes the bulk node B of a MOSFET device to be connected to the source terminal if the port
node B is left unconnected:
Ports −> {"D", "G", "S", Optional["B", "S"]}
You can also tell Analog Insydes to leave an unconnected node floating by using Optional without
a second argument. The following Ports declaration treats S as if it were an internal node of the
model definition if S is left unconnected.
Ports −> {"C", "B", "E", Optional["S"]}
The second node given in an Optional declaration must be a required port, an internal
node of the model definition, or the global ground node.
Parameters
Parameters−>{parspec
, parspec
, † † † }
specify the symbols which represent parameters of a model
definition
Format of the Parameters argument.
With the Parameters keyword, you can specify the set of symbols which represent the parameters
of a model definition. Possible values are:
symbol
Global[symbol]
declare symbol as an instance-specific model parameter
declare symbol as a global quantity but allow
instance-specific value assignments
Values for the parameter specification parspec.