Forums

PSpice worst case simulation

Started by Joerg March 21, 2011
Hi Folks,

Reached an end of a rope here: How do you make a worst case simulation
in PSpice (or even Monte Carlo for that matter) properly find the
extremes for an opamp offset voltage and input bias current?

For example, for the opamp we have:

VOS: Offset voltage
VOS_DIST: Distribution, I assume
VOS_NTOL: What gets entered here?
VOS_PTOL: ... and here?

If I enter 7mV or whatever for VOS and set the distributuion to flat the
sim acts as if there was always +7mV. No variation. But we all know that
it'll be +/-7mV. How can I make PSpice understand that? The manual
appears to be silent about it and a web search doesn't even find
expressions such as VOS_NTOL.

Same goes for input bias current except that there it's called IB,
IB_DIST, IB_NTOL and IB_PTOL. Having to massage all these by hand gets
old in a larger simulation.

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
On Mon, 21 Mar 2011 16:10:43 -0700, Joerg <invalid@invalid.invalid>
wrote:

>Hi Folks, > >Reached an end of a rope here: How do you make a worst case simulation >in PSpice (or even Monte Carlo for that matter) properly find the >extremes for an opamp offset voltage and input bias current? > >For example, for the opamp we have: > >VOS: Offset voltage >VOS_DIST: Distribution, I assume >VOS_NTOL: What gets entered here? >VOS_PTOL: ... and here? > >If I enter 7mV or whatever for VOS and set the distributuion to flat the >sim acts as if there was always +7mV. No variation. But we all know that >it'll be +/-7mV. How can I make PSpice understand that? The manual >appears to be silent about it and a web search doesn't even find >expressions such as VOS_NTOL. > >Same goes for input bias current except that there it's called IB, >IB_DIST, IB_NTOL and IB_PTOL. Having to massage all these by hand gets >old in a larger 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 = 7mv, VOS_PTOL = 7mv At least, that is what I think it should be. Could be NTOL should be -7mV... Charlie
On Mon, 21 Mar 2011 16:10:43 -0700, Joerg <invalid@invalid.invalid>
wrote:

>Hi Folks, > >Reached an end of a rope here: How do you make a worst case simulation >in PSpice (or even Monte Carlo for that matter) properly find the >extremes for an opamp offset voltage and input bias current? > >For example, for the opamp we have: > >VOS: Offset voltage >VOS_DIST: Distribution, I assume >VOS_NTOL: What gets entered here? >VOS_PTOL: ... and here? > >If I enter 7mV or whatever for VOS and set the distributuion to flat the >sim acts as if there was always +7mV. No variation. But we all know that >it'll be +/-7mV. How can I make PSpice understand that? The manual >appears to be silent about it and a web search doesn't even find >expressions such as VOS_NTOL. > >Same goes for input bias current except that there it's called IB, >IB_DIST, IB_NTOL and IB_PTOL. Having to massage all these by hand gets >old in a larger simulation.
First order of business... does your OpAmp MODEL support MC parameterization? Confucius further says, "He who lives by Crapture, dies by Crapture" ;-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Remember: Once you go over the hill, you pick up speed
Charlie E. wrote:
> On Mon, 21 Mar 2011 16:10:43 -0700, Joerg <invalid@invalid.invalid> > wrote: > >> Hi Folks, >> >> Reached an end of a rope here: How do you make a worst case simulation >> in PSpice (or even Monte Carlo for that matter) properly find the >> extremes for an opamp offset voltage and input bias current? >> >> For example, for the opamp we have: >> >> VOS: Offset voltage >> VOS_DIST: Distribution, I assume >> VOS_NTOL: What gets entered here? >> VOS_PTOL: ... and here? >> >> If I enter 7mV or whatever for VOS and set the distributuion to flat the >> sim acts as if there was always +7mV. No variation. But we all know that >> it'll be +/-7mV. How can I make PSpice understand that? The manual >> appears to be silent about it and a web search doesn't even find >> expressions such as VOS_NTOL. >> >> Same goes for input bias current except that there it's called IB, >> IB_DIST, IB_NTOL and IB_PTOL. Having to massage all these by hand gets >> old in a larger 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 = > 7mv, VOS_PTOL = 7mv > > At least, that is what I think it should be. Could be NTOL should be > -7mV... >
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 ;-) -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Jim Thompson wrote:
> On Mon, 21 Mar 2011 16:10:43 -0700, Joerg <invalid@invalid.invalid> > wrote: > >> Hi Folks, >> >> Reached an end of a rope here: How do you make a worst case simulation >> in PSpice (or even Monte Carlo for that matter) properly find the >> extremes for an opamp offset voltage and input bias current? >> >> For example, for the opamp we have: >> >> VOS: Offset voltage >> VOS_DIST: Distribution, I assume >> VOS_NTOL: What gets entered here? >> VOS_PTOL: ... and here? >> >> If I enter 7mV or whatever for VOS and set the distributuion to flat the >> sim acts as if there was always +7mV. No variation. But we all know that >> it'll be +/-7mV. How can I make PSpice understand that? The manual >> appears to be silent about it and a web search doesn't even find >> expressions such as VOS_NTOL. >> >> Same goes for input bias current except that there it's called IB, >> IB_DIST, IB_NTOL and IB_PTOL. Having to massage all these by hand gets >> old in a larger simulation. > > First order of business... does your OpAmp MODEL support MC > parameterization? >
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.
> Confucius further says, "He who lives by Crapture, dies by Crapture" > ;-) >
But Confucius also say customer is king and if customer want Capture then use Capture :-) -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
On Mon, 21 Mar 2011 16:46:05 -0700, Joerg <invalid@invalid.invalid>
wrote:

>Charlie E. wrote: >> On Mon, 21 Mar 2011 16:10:43 -0700, Joerg <invalid@invalid.invalid> >> wrote: >> >>> Hi Folks, >>> >>> Reached an end of a rope here: How do you make a worst case simulation >>> in PSpice (or even Monte Carlo for that matter) properly find the >>> extremes for an opamp offset voltage and input bias current? >>> >>> For example, for the opamp we have: >>> >>> VOS: Offset voltage >>> VOS_DIST: Distribution, I assume >>> VOS_NTOL: What gets entered here? >>> VOS_PTOL: ... and here? >>> >>> If I enter 7mV or whatever for VOS and set the distributuion to flat the >>> sim acts as if there was always +7mV. No variation. But we all know that >>> it'll be +/-7mV. How can I make PSpice understand that? The manual >>> appears to be silent about it and a web search doesn't even find >>> expressions such as VOS_NTOL. >>> >>> Same goes for input bias current except that there it's called IB, >>> IB_DIST, IB_NTOL and IB_PTOL. Having to massage all these by hand gets >>> old in a larger 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 = >> 7mv, VOS_PTOL = 7mv >> >> At least, that is what I think it should be. Could be NTOL should be >> -7mV... >> > >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 ;-)
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 -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Remember: Once you go over the hill, you pick up speed
Jim Thompson wrote:
> On Mon, 21 Mar 2011 16:46:05 -0700, Joerg <invalid@invalid.invalid> > wrote: > >> Charlie E. wrote: >>> On Mon, 21 Mar 2011 16:10:43 -0700, Joerg <invalid@invalid.invalid> >>> wrote: >>> >>>> Hi Folks, >>>> >>>> Reached an end of a rope here: How do you make a worst case simulation >>>> in PSpice (or even Monte Carlo for that matter) properly find the >>>> extremes for an opamp offset voltage and input bias current? >>>> >>>> For example, for the opamp we have: >>>> >>>> VOS: Offset voltage >>>> VOS_DIST: Distribution, I assume >>>> VOS_NTOL: What gets entered here? >>>> VOS_PTOL: ... and here? >>>> >>>> If I enter 7mV or whatever for VOS and set the distributuion to flat the >>>> sim acts as if there was always +7mV. No variation. But we all know that >>>> it'll be +/-7mV. How can I make PSpice understand that? The manual >>>> appears to be silent about it and a web search doesn't even find >>>> expressions such as VOS_NTOL. >>>> >>>> Same goes for input bias current except that there it's called IB, >>>> IB_DIST, IB_NTOL and IB_PTOL. Having to massage all these by hand gets >>>> old in a larger 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 = >>> 7mv, VOS_PTOL = 7mv >>> >>> At least, that is what I think it should be. Could be NTOL should be >>> -7mV... >>> >> 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 ;-) > > Did you read the IntuSoft reference I sent? >
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.
> 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. >
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. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
PD says:
> And you seem to think that there is some set of "prime definitions" > that people should agree on. What gives you that idea? >
xxein says: Then there is no common understanding of anything except for myirad beliefs.
Jim Thompson wrote:
> On Mon, 21 Mar 2011 17:07:27 -0700, Joerg <invalid@invalid.invalid> > wrote: > >> Jim Thompson wrote: >>> On Mon, 21 Mar 2011 16:46:05 -0700, Joerg <invalid@invalid.invalid> >>> wrote: >>> >>>> Charlie E. wrote: >>>>> On Mon, 21 Mar 2011 16:10:43 -0700, Joerg <invalid@invalid.invalid> >>>>> wrote: >>>>> >>>>>> Hi Folks, >>>>>> >>>>>> Reached an end of a rope here: How do you make a worst case simulation >>>>>> in PSpice (or even Monte Carlo for that matter) properly find the >>>>>> extremes for an opamp offset voltage and input bias current? >>>>>> >>>>>> For example, for the opamp we have: >>>>>> >>>>>> VOS: Offset voltage >>>>>> VOS_DIST: Distribution, I assume >>>>>> VOS_NTOL: What gets entered here? >>>>>> VOS_PTOL: ... and here? >>>>>> >>>>>> If I enter 7mV or whatever for VOS and set the distributuion to flat the >>>>>> sim acts as if there was always +7mV. No variation. But we all know that >>>>>> it'll be +/-7mV. How can I make PSpice understand that? The manual >>>>>> appears to be silent about it and a web search doesn't even find >>>>>> expressions such as VOS_NTOL. >>>>>> >>>>>> Same goes for input bias current except that there it's called IB, >>>>>> IB_DIST, IB_NTOL and IB_PTOL. Having to massage all these by hand gets >>>>>> old in a larger 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 = >>>>> 7mv, VOS_PTOL = 7mv >>>>> >>>>> At least, that is what I think it should be. Could be NTOL should be >>>>> -7mV... >>>>> >>>> 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 ;-) >>> Did you read the IntuSoft reference I sent? >>> >> 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. >> >> >>> 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. >>> >> 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? >
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: http://www.analogconsultants.com/ng/sed/LM324_pspice.jpg 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. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
On Mon, 21 Mar 2011 17:47:14 -0700, Joerg <invalid@invalid.invalid>
wrote:

>Jim Thompson wrote: >> On Mon, 21 Mar 2011 17:07:27 -0700, Joerg <invalid@invalid.invalid> >> wrote: >> >>> Jim Thompson wrote: >>>> On Mon, 21 Mar 2011 16:46:05 -0700, Joerg <invalid@invalid.invalid> >>>> wrote: >>>> >>>>> Charlie E. wrote: >>>>>> On Mon, 21 Mar 2011 16:10:43 -0700, Joerg <invalid@invalid.invalid> >>>>>> wrote: >>>>>> >>>>>>> Hi Folks, >>>>>>> >>>>>>> Reached an end of a rope here: How do you make a worst case simulation >>>>>>> in PSpice (or even Monte Carlo for that matter) properly find the >>>>>>> extremes for an opamp offset voltage and input bias current? >>>>>>> >>>>>>> For example, for the opamp we have: >>>>>>> >>>>>>> VOS: Offset voltage >>>>>>> VOS_DIST: Distribution, I assume >>>>>>> VOS_NTOL: What gets entered here? >>>>>>> VOS_PTOL: ... and here? >>>>>>> >>>>>>> If I enter 7mV or whatever for VOS and set the distributuion to flat the >>>>>>> sim acts as if there was always +7mV. No variation. But we all know that >>>>>>> it'll be +/-7mV. How can I make PSpice understand that? The manual >>>>>>> appears to be silent about it and a web search doesn't even find >>>>>>> expressions such as VOS_NTOL. >>>>>>> >>>>>>> Same goes for input bias current except that there it's called IB, >>>>>>> IB_DIST, IB_NTOL and IB_PTOL. Having to massage all these by hand gets >>>>>>> old in a larger 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 = >>>>>> 7mv, VOS_PTOL = 7mv >>>>>> >>>>>> At least, that is what I think it should be. Could be NTOL should be >>>>>> -7mV... >>>>>> >>>>> 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 ;-) >>>> Did you read the IntuSoft reference I sent? >>>> >>> 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. >>> >>> >>>> 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. >>>> >>> 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? >> > >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: > >http://www.analogconsultants.com/ng/sed/LM324_pspice.jpg > >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 -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Remember: Once you go over the hill, you pick up speed