Question: I would like to sweep a resistor in DC analysis so that I can plot the
resistance along the X-axis versus my voltage and current plots. How do I do this?
Answer: For a DC analysis sweep you need the MODEL attribute for a resistor
defined. Do the following:
1) For the resistor that you want to sweep, double click on that resistor and define
the MODEL attribute. For this example, we will use the name RMod. Make sure that
the model name is unique to this resistor in the schematic. Set the RESISTANCE attribute
value to 1 (I'll explain why in the following step).
2) Go to DC analysis. For Variable 1, choose the appropriate resistor model in the Name
attribute from the drop down list. You should see an entry such as RES RMod in the list
if the model name was RMod. Set the second field so it specifies the R parameter. In
the Range field, enter the range that you would like the resistance swept through. The
R parameter is a multiplier and multiplies the Resistance value. That is why we set the
Resistance attribute to 1 previously so that we can sweep R with the actual resistance
values directly in the Range field.
Question: I need to create a resistor that varies with the voltage of a node in
my circuit. How do I model this?
Answer: Simply enter the expression that you want to use into the RESISTANCE
attribute of the resistor. For example, if you wanted the resistor to reference the
voltage at node Mod, you would use V(Mod) in the expression. You can combine this
with other operators or circuit variables to create any number of equations.
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