User Guide

DC Sweep
221
Curve families for DC sweeps
When a nested DC sweep is performed, the entire curve
family is displayed. That is, the nested DC sweep is
treated as a single data section (or you can think of it as a
single PSpice run).
For the circuit shown in Figure 57, you can set up a DC
sweep analysis with an outer sweep of the voltage source
VD and an inner sweep of the voltage source VG as listed
in Tabl e 1
.
When the DC sweep analysis is run, add a current marker
at the drain pin of M1 and display the simulation results
in PSpice. The result will look like Figure 58.
To add a load line for a resistor, add a trace that computes
the load line from the sweep voltage. Assume that the X
axis variable is the sweep voltage V_VD, which runs from
0 to 5 volts. The expression which will add a trace that is
the load line for a 50 kohm resistor is:
(5V-V_VD)/50K
This can be useful for determining the bias point for each
member of a curve family as shown in Figure 59.
Table 1 Curve family example setup
Outer sweep Nested sweep
Swept Var Type voltage source voltage source
Sweep Type linear linear
Name VD VG
Start Value 0 0
End Value 5 2
Increment 0.1 0.5
Figure 57
Curve family example
schematic.
In Capture,
f
rom t
h
e PSpice menu, point to
Markers, then choose Mark Current Into Pin
to add a current marker.
V_VD is t
h
e
h
ierarc
h
ica
l
name
f
or VD
created by netlisting the schematic.
Pspug.book Page 221 Wednesday, November 11, 1998 1:14 PM