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2.3 Circuits and Subcircuits 65
In[21]:= darlWithoutModels =
Circuit[
Netlist[
{I1, {0, 1}, 1},
{Q1, {1 −> "B", 2 −> "C", 3 −> "E"},
Model −> NPNTransistor, Selector −> ACsimple,
RB −> RB1, beta −> 150},
{Q2, {3 −> "B", 2 −> "C", 0 −> "E"},
Model −> NPNTransistor, Selector −> ACsimple,
beta −> beta2},
{Load, {0, 2}, Type −> Resistor, Value −> RL,
Pattern −> Impedance}
]
];
In[22]:= ExpandSubcircuits[darlWithoutModels] // DisplayForm
Out[22]//DisplayForm=
Netlist Flat, 6 Entries:
I1, 0, 1, 1
RB$Q1, X$Q1, 3, RB1
CC$Q1, 1, X$Q1, 2, 3, 150
RB$Q2, X$Q2, 0, RB$Q2
CC$Q2, 3, X$Q2, 2, 0, beta2
Load, 0, 2, Type Resistor, Value RL, Pattern Impedance
Redefining and Removing Global Subcircuits
If ExpandSubcircuits or CircuitEquations is called on a Circuit object containing a global model
definition, any previously stored model in the global database with the same Name and Selector
arguments is replaced by the new one. To remove a particular subcircuit from the global database
we can use the command RemoveSubcircuit (Section 3.3.8). Its arguments must be the name and
the selector of the subcircuit definition to be deleted. The return value is a list of the names and
selectors of the remaining subcircuit definitions. For example, let’s remove the transistor model
NPNTransistor/ACdynamic. The only remaining model is then NPNTransistor/ACsimple:
In[23]:= RemoveSubcircuit[NPNTransistor, ACdynamic]
Out[23]= NPNTransistor, ACsimple
Locally Overriding Global Subcircuit Definitions
One further application of the Scope argument is that we can locally override a global subcircuit
definition. Local subcircuits always take precedence over global definitions with the same name and
selector without overwriting the global definition. To illustrate this, let’s temporarily replace the
NPNTransistor/ACsimple model with the subcircuit shown in Figure 3.4. The difference between
the original implementation of NPNTransistor/ACsimple and this model is that the latter contains a
voltage-controlled current source VCCS (Section 4.2.13) instead of a current-controlled current source
CCCS (Section 4.2.11).