Plotting a signal against another with orcad pspice.

Hi,
I am new to pspice and need help manipulating some plots. I'm used to doing this in cadence but can't figure out how to do that in pspice. Suppose I have two curves:
y(x) and z(x) where x is Vgs of a mosfet.
I want to now plot y(x) against z(x).
Is there a built in capability to do That?
Thanks

Did you read the "Viewing waveforms" paragraph in the PSpice user guide? It explains how you can set the x-axis to a different variable.

E.g. in a Vgs DC sweep, you'll have Vgs as default x-axis. But you can change it to any other variable recorded during simulation.

FvM said:

Did you read the "Viewing waveforms" paragraph in the PSpice user guide? It explains how you can set the x-axis to a different variable.

E.g. in a Vgs DC sweep, you'll have Vgs as default x-axis. But you can change it to any other variable recorded during simulation.

Click to expand...

Hi FvM,
The information that I found in the pspice user guide did not help with what I want to do. I don't want to plot a given signal against another variable but rather a curve against another curve. "Plot-->Axis Settings...-->Axis Variable" allows me to choose a different variable for my x-axis. What I really want is: I have y(x) and z(x) plotted and now I want to plot y(x) against z(x). I can't remember the actual command name in Cadence Virtuoso but I used to do that all the time. Unfortunately I don't have access to Cadence anymore.

Thanks

Seriously I don't understand the difference between plotting against "another curve" and "another variable". Curves are representing analysis variables, isn't it?

You may want to give an example of what you want to achieve.

The first attachment has two plot windows. The first plot window is the plot of the overdrive voltage with respect to vgs.
The second window is gm/id curves with respect to vgs.
Now I want to plot the traces in window2 against traces in window1.

The second attchment is what I get when I try to manipulate the waveforms as described above. It only lists branch currents and node voltages as valid variables. The overdrive voltage is a derived expression so it's not shown as a variable. My question in effect is, is there a way to specify the overdrive voltage as a variable so it can be used as the x-axis?

At the bottom of the second attachment , in the field "Trace Expression, I tried to express the overdrive voltage explicitly as Vgs-Vt but I get an error as shown below:


I've tried a number of formats in the "Trace Expression" field like adding double quotes, single quotes etc.. but so far I've not been successful.

any suggestions?

What's against generating the intended x variable as an auxiliary node voltage?

What's against generating the intended x variable as an auxiliary node voltage?

Click to expand...

I think that is done in PSpice using the ABM block. You can generate your "window 2" as an auxiliary variable i.e. node, and then you do it the same way as you did so far.

Quick update: The first try using ABM blocks resulted in the same error as attached previously. In troubleshooting the error, I realized that the first method of defining Vgs-Vt explicitly in the "Trace Expression" field worked just fine. The error is due to the fact I'm running a parametric sweep so Vgs-Vt is actually a family of curves. Essentially the x-axis can't be a family of curves. If I turn off the parametric sweep then both methods work just fine; I get the plot that I expect. Since I need to run parametric sweeps to have useful gm/id curves, it looks like exporting the data and using external tools might be the only way to do this.