User`s guide

12
-
8 Parametric and Temperature Analysis
Example: Frequenc
y
Response
vs. Arbitrar
y
Parameter
A common request is to view a plot of the linear response of a
circuit at a specific frequency as one of the circuit parameters
varies (such as the output of a band pass filter at its center
frequency vs. an inductor value). In this example, the value of a
nonlinear capacitance is measured using a 10 kHz AC signal and
plotted vs. its bias voltage. The capacitance is in parallel with a
resistor, so a Probe expression is used to calculate the
capacitance from the complex admittance of the R-C pair.
This technique for measuring branch capacitances works well in
both simple and complex circuits.
Settin
g
up the circuit
Enter the circuit in Schematics as shown in Figure 12-5
To create the capacitor model in the schematic editor:
1
Place a Cbreak symbol.
2
Select it so that it is highlighted.
3
Select Model from the Edit menu.
4
Select Edit Instance Model Text. Enter the following:
.model Cnln CAP(C=1 VC1=-0.01 VC2=0.05)
Set up the circuit for a parametric AC analysis (sweep Vbias),
and run PSpice A/D. Include only the frequency of interest in
the AC sweep.
Fi
g
ure 12-5
RLC Filter Example
Circuit