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62 2. Tutorial
same global symbols to all instances of the corresponding subcircuit element values. This would not
be very convenient as it would require typing something along the line of R$X1 ⩵ R$X2 ⩵ R$X3 ⩵ ⩵
R for every group of identical elements. By explicitly declaring which symbols in a subcircuit denote
parameters and quietly assuming all others to be global quantities, cases like that of the Darlington
amplifier as well as that of the ladder circuit are both dealt with most easily. However, Analog
Insydes provides the command MatchSymbols which applies matching information on a DAEObject.
Thus, you can decide which parameters to match even after setting up the equation system.
Passing Parameter Values to Subcircuit Instances
Though intentional and useful, the automatic instantiation of symbolic subcircuit parameters is only
a side effect of the parameter declaration. The original purpose of the Parameters argument in a
Model definition is to declare the set of local model variables which can be replaced by instancespecific
values given in the value fields of subcircuit references (see Section 3.1.8). In other words,
we can pass parameter values to a subcircuit in a similar way as we can pass arguments to a function
defined in Mathematica. Since we do not have to specify values for model parameters, automatic
instantiation comes into effect whenever a default value is needed for a parameter which has not
been assigned a value.
If we need to pass parameter values to instances of subcircuit objects we must append a sequence
of replacement rules of the form
parameter symbol −> value
to the value field of the corresponding subcircuit references. The full netlist format of a subcircuit
reference is thus
{subcircuit instance name, {port connections},
Model −> subcircuit class name, Selector −> selector,
parameter 1 −> value 1 , parameter 2 −> value 2 , }
To illustrate the possible cases consider the netlist of the Darlington amplifier from Section 2.3.5 (see
Figure 3.3) once again. Let’s assign the symbolic value RB1 and a numerical value of to the
parameters RB and beta of Q1, respectively. In the case of Q2, we assign the symbol beta2 to the
current gain whereas we leave the parameter RB unspecified.