Discussion in 'Homework Help' started by db0006, Feb 8, 2007.

1. ### db0006 Thread Starter New Member

Feb 8, 2007
2
0
Hi there,

If I have an AC source, how do I sweep a variable on the x axis?

For example, if I had a DC source, and wanted to vary a resistor and plot it against the voltage output, I'd simply use DC sweep and select global paramter for my resistor. This would give me the resistor sweep on the x axis, and I could add a trace to get the voltage output on the Y axis.

The problem is, I'm using an AC source. So if I take the same steps as above, I'm asked if I'd like to anylise in DC or transitent. If I select DC, I get no voltage (because I have an AC source?). If I choose transient, I'm stuck with the time on the x axis.

Hopefully there is some PSPICE experts out there. Thanks in advance : )

-Dan

2. ### Distort10n Active Member

Dec 25, 2006
429
1
Are you trying to plot voltage vs. resistance across a varying resistance with an AC source?

I do not see how you can do that and have a decent graph. Since an AC source is time varying, what would the voltage be for a given resistance value?

Anyone know if PSpice can do 3-D graphs?

3. ### n9352527 AAC Fanatic!

Oct 14, 2005
1,198
4
There is currently no easy way to plot a sweep parameter under transient condition of AC source.

As you can imagine, AC source implies time dependent voltage and if you add another sweep parameter then you'd actually vary this parameter under varying AC voltage. You end up with a sweep within a sweep.

You could do transient analysis and sweep the parameter, like you've already done. However, like you've found out already, the software would plot time as X axis, because it can't correlate which 'point in time' data you'd want to plot for your varying parameter.

The only way to overcome this is to load your data to another plotting software, like Matlab or Octave and then manipulate it yourself. Or extract the data you want manually and then transfer them to Excel or something like that.

BTW, AC analysis does frequency related sweep, and not voltage related sweep.

No 3D graphs yet in SPICE, that's where Matlab or Octave come in

Oct 14, 2005
1,198
4
Double post.

5. ### db0006 Thread Starter New Member

Feb 8, 2007
2
0
Thx for the responces.

I actually managed to find an option in PSPICE. Under the trace menu you can select "performance analysis" and after messing around in there for awhile, I actually obtained a graph with a sweep of selected variable.