PSpice worst case simulation

Joerg, Well, that should be VOS: Offset voltage, VOS_DIST: Distribution type, probably FLAT VOS_NTOL: Negative tolerance VOS_PTOL: Positive tolerance

So, if you wanted +/- 7mV, then VOS = 0, VOS_DIST = FLAT, VOS_NTOL =

At least, that is what I think it should be. Could be NTOL should be

-7mV...

Charlie

First order of business... does your OpAmp MODEL support MC parameterization?

Confucius further says, "He who lives by Crapture, dies by Crapture" ;-) ...Jim Thompson

I had already tried both. It no workie :-(

Looked around to find a description of this stuff but no dice either. Maybe this is restricted to an inner circle of gurus who know the secret knock on the back door ;-)

For the test it's an LM324. I took it from the PSpice advanced analysis directory and assume (but not sure) that PSpice should have sounded some siren if it wasn't MC-ready and you run a MC. Plus it has all the entry fields.

But Confucius also say customer is king and if customer want Capture then use Capture :-)

Did you read the IntuSoft reference I sent?

Did you take heed of my previous post... "First order of business... does your OpAmp MODEL support MC parameterization?"

If it isn't parameterized in the model, you're dead in the water. ...Jim Thompson

Yes, I read that and the others cover to cover. But VOS isn't described in there. It describes how to do MC and worst case on LOT and DEV variations in BJTs and so on. I only need to do worst case, plus MC as a sanity check.

Ok, but how does one know? Why would it have a gazillion attribute entries such as VOS_NTOL and VOS_PTOL if those can't be used? AFAIU worst case and MC are the only sims that could use such information. I'd expect PSpice to refuse entry if I tried entering data that isn't supported by a model.

None of the LM324 models I have on hand show DEV or LOT in the model card. Can you post your model so I can see? ...Jim Thompson

The LM324 model doesn't have DEV and LOT (I don't need both) but it does have fields for high/low of the offset parameters and various others:

If this model can't support MC or worst case, why would there even be those Postol and Negtol fields? They appear to be editable because when I change them the values stick.

Crapture has changed the entry method for doing analysis.... obviously not for the better :-)

I just opened my copy of Crapture, v10.5i, so it's dated and likely differs from yours...

Click on PSpice, Edit Simulation profile, Monte Carlo/Worst Case.

What do you have entered there? ...Jim Thompson

That's still the same in 16.3. It is set to Monte Carlo, output variable to output node of opamp, 10 runs, uniform distribution, save all data.

I also tried worst case, same thing, won't wiggle the opamp offset a bit. It does work on resistors and stuff though. Although even there PSpice is a bit odd because it only lets you find the min _or_ the max of the output, but not both together in one plot. Doesn't make sense, but then again it seems a few other things don't make much sense either.

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You've discovered my point... look at this model...

.MODEL N1 NPN (IS=5E-16 LOT/UNIFORM=90% DEV/GAUSS=3%)

• BF=220 LOT/UNIFORM=50% DEV/GAUSS=2%)

• BR=0.7 NR=1

• ISE=3.5E-16 IKF=3E-3 IKR=3E-2 NE=1.4 NC=0.8 VAF=60

• VAR=7 RC=15 RE=2 RB=200 RBM=100 IRB=3E-4 XTB=1.17

• XTI=2.2 EG=1.235 TF=69.09E-12 TR=9E-9 XTF=0.3 VTF=6

• ITF=5E-5 CJE=0.105E-12 MJE=0.8 VJE=0.8 ISC=1E-15

• KF=2E-13 AF=1.4

Does your OpAmp model have those LOT and DEV entries? ...Jim Thompson

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No, it doesn't. Other opamps don't either, so far I only saw them in discretes. Why would it need them if there are NTOL and PTOL entries?

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If they're not in the model....

Why aren't you watching "Dances"? I'm on a commercial break :-) ...Jim Thompson

Joerg, Don't know for sure, but those may be Advanced Analysis parameter, only useful if you have the AA option for PSpice. They didn't sound familiar to me from plain vanilla...

Charlie

Ok, I bet you don't have Advanced Analysis, or if you do, you aren't using the Advanced Analysis menu to do the WC and MC sims. They are in a different place than the regular menus in the simulation profile!

Charlie

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But then why wouldn't those fields be grayed out or refusing entries in the simulator? I can enter data there and it sticks, meaning after saving it's still there.

Oh, I was. But on the couch and half dozed off. Caught some sort of flu bug :-(

This season there are some really good candidates, lots of talent. And Bruno is promising to live up to his usual exuberant outbursts pretty soon.

Yes, that's what I am afraid may be true. I'll open a support ticket then, to find out for sure. I just wonder, what good would it do if they provide worst case analysis in the regular PSpice and then you can't scoot an offset for tolerance?

I don't have the license for Advanced. But the menu items I described where in regular PSpice. They just don't do anything there.

I don't quite know how this "advanced" stuff is supposed to work, but you can still do MC and WC... just modify your models as I noted previously. ...Jim Thompson