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2.2 Netlists 45
{VCC, {1, 0}, Type −> VoltageSource, Value −> VCC}
Pattern
The Pattern option (see Section 3.1.4) can be used only in conjunction with two-terminal immittances,
i.e. impedance and admittance elements such as resistors (Section 4.2.1), conductances (Section 4.2.2),
capacitors (Section 4.2.5), and inductors (Section 4.2.6). With this directive you can explicitly choose
whether the contribution of an immittance element to a system of modified nodal equations is
entered into the matrix using the fill-in pattern for admittances or the pattern for impedances. The
two associated values of the Pattern option are Impedance and Admittance.
When setting up modified nodal equations, Analog Insydes automatically converts impedance
elements such as resistors into their admittance equivalents in order to keep the matrix size as
small as possible. In other words, a resistor with the value R will be treated as an admittance
with the value R and will be entered into the modified nodal matrix using the fill-in pattern
for admittances (see the example in Section 2.2.3). However, if we are interested in computing the
current through a particular resistor it would be better to use the fill-in pattern for impedances
as this would augment the MNA system by the corresponding branch current. So if we want to
calculate the load current of the above-mentioned amplifier using the MNA formulation we would
have to select the impedance pattern for the load resistor in order to introduce the branch current
I$Load:
{Load, {out, 0}, Type −> Resistor, Value −> RL,
Pattern −> Impedance}
Let’s experiment with some value-field options using the CCCS circuit from Section 2.2.2 (see
Figure 2.7). We replace the resistor RL by a variable load type and select the fill-in pattern for
impedances.
In[15]:= cccsCircuit2 =
Netlist[
{V0, {1, 0}, V0},
{RB, {1, 3}, RB},
{CM, {1, 2}, CM},
{CC1, {3, 0, 2, 0}, beta},
{Load, {2, 0}, Type −> loadtype, Value −> loadval,
Pattern −> Impedance}
]
Out[15]= NetlistRaw, 5
We choose a resistive load with the symbolic value RL and set up the MNA equations. Due to the
Pattern directive, the load current I$Load now appears as an additional variable for which we can
solve directly.