User Guide

Parametric analysis
279
To display the results
Use PSpice to display the capacitance calculated at the
frequency of interest versus the stepped parameter.
1 Simulate the circuit.
2 Load all AC analysis sections.
3 From the Trace menu, choose Add Trace or click the
Add Trace toolbar button.
4 Add the following trace expression:
IMG(-I(Vin)/V(1,0))/(2*3.1416*Frequency)
Or add the expression:
CvF(-I(Vin)/V(1,0))
Where CvF is a macro which measures the effective
capacitance in a complex conductance. Macros are defined
using the Macros command on the Trace menu. The CvF
macro should be defined as:
CvF(G)= IMG(G)/(2*3.1416*Frequency)
Note
-I(Vin)/V(1) is the complex admittance of the R-C branch; the
minus sign is required for correct polarity.
To use performance analysis to plot capacitance vs. bias voltage
1 From the Trace menu, choose Performance Analysis.
2 Click Wizard.
3 Click Next>.
4 Click YatX in the Choose a Goal Function list, and then
click Next>.
5 In the Name of Trace text box, type the following:
CvF(-I(Vin)/V(1))
6 In the X value to get Y value at text box, type 10K.
7 Click Next>.
The wizard displays the gain trace for the first run to
text the goal function (YatX).
8 Click Finish.
Pspug.book Page 279 Wednesday, November 11, 1998 1:14 PM