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64 2. Tutorial
appropriate Scope argument (see Section 3.2.1). Scope has two possible values, Local and Global.
To make a subcircuit available globally, we need to set the scope as follows:
Scope −> Global
By expanding a circuit which contains only model definitions with global scope we can implement a
globally accessible model library in our current Mathematica environment. For example, let’s set up
a model library from the two NPN transistor models NPNTransistor/ACsimple and
NPNTransistor/ACdynamic from Section 2.3.2 (see Figure 3.2).
In[19]:= Circuit[
Model[
Name −> NPNTransistor,
Selector −> ACsimple,
Scope −> Global,
Ports −> {"B", "C", "E"},
Parameters −> {RB, beta},
Definition −>
Netlist[
{RB, {"X", "E"}, RB},
{CC, {"B", "X", "C", "E"}, beta}
]
],
Model[
Name −> NPNTransistor,
Selector −> ACdynamic,
Scope −> Global,
Ports −> {"B", "C", "E"},
Parameters −> {RB, CM, beta, RO},
Definition −>
Netlist[
{RB, {"X", "E"}, RB},
{CM, {"B", "C"}, CM},
{CC, {"B", "X", "C", "E"}, beta},
{RO, {"C", "E"}, RO}
]
]
] // ExpandSubcircuits;
Both models are now stored in the global subcircuit database and can thus be referenced by any other
netlist. Note that simply defining the models is not sufficient for storing them in the global database –
we have to call ExpandSubcircuits in order to store them into the global database. If the Circuit
object contains a top-level Netlist, a call to CircuitEquations stores the models in the global
database, too. We can check the contents of the database using the command GlobalSubcircuits
(Section 3.3.4), which will return a list of the names and selectors of the global subcircuits.
In[20]:= GlobalSubcircuits[]
Out[20]=
NPNTransistor, ACdynamic, NPNTransistor, ACsimple
The global definition of the transistor models allows us to write the circuit description of the
Darlington amplifier from Section 2.3.5 (see Figure 3.3) without the Model commands. Then, during
subcircuit expansion, the global database will be searched for models which are not defined locally.