Forums

PSpice worst case simulation

Started by Joerg March 21, 2011
On Tue, 22 Mar 2011 10:49:21 -0700, Joerg <invalid@invalid.invalid>
wrote:

> >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?
To be honest, it all depends on the models. Most opamp models don't have those variable set up to tolerance offsets, etc. The AdvAnal models were custom made to be able to add in all those extras, to justify some of the added expense of the option! You can always modify the existing models to add those tolerances. Jim gave you a few clues on how to do that. Charlie
On Tue, 22 Mar 2011 11:58:51 -0700, Charlie E. <edmondson@ieee.org>
wrote:

>On Tue, 22 Mar 2011 10:49:21 -0700, Joerg <invalid@invalid.invalid> >wrote: > >> >>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? > >To be honest, it all depends on the models. Most opamp models don't >have those variable set up to tolerance offsets, etc. The AdvAnal >models were custom made to be able to add in all those extras, to >justify some of the added expense of the option! > >You can always modify the existing models to add those tolerances. Jim >gave you a few clues on how to do that. > >Charlie
I even sent him a detailed treatise from IntuSoft, but I fear that Joerg has no experience rolling his own models. He needs to practice up on making subcircuits and behavioral things... hone up his math ;-) I can't even fathom a large enough number to count all the models I've made. I'm fond of making my own tool devices... that automatically do all the things that LTspice calls up as "Measure"... my tools display the results in Probe :-) ...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 Tue, 22 Mar 2011 11:58:51 -0700, Charlie E. <edmondson@ieee.org> > wrote: > >> On Tue, 22 Mar 2011 10:49:21 -0700, Joerg <invalid@invalid.invalid> >> wrote: >> >>> 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? >> To be honest, it all depends on the models. Most opamp models don't >> have those variable set up to tolerance offsets, etc. The AdvAnal >> models were custom made to be able to add in all those extras, to >> justify some of the added expense of the option! >> >> You can always modify the existing models to add those tolerances. Jim >> gave you a few clues on how to do that. >> >> Charlie > > I even sent him a detailed treatise from IntuSoft, but I fear that > Joerg has no experience rolling his own models. He needs to practice > up on making subcircuits and behavioral things... hone up his math ;-) >
Oh, I've made models in the past. Just not opamps, and not with a pounding flu-infested head like right now ;-)
> I can't even fathom a large enough number to count all the models I've > made. I'm fond of making my own tool devices... that automatically do > all the things that LTspice calls up as "Measure"... my tools display > the results in Probe :-) >
Maybe I just place a voltage source in front of every opamp and let it step the voltage. I can already hear the comments ... "GAAAAAH" ... and ... "EEEUW" ... :-) -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
On Tue, 22 Mar 2011 12:43:19 -0700, Joerg <invalid@invalid.invalid>
wrote:

>Jim Thompson wrote: >> On Tue, 22 Mar 2011 11:58:51 -0700, Charlie E. <edmondson@ieee.org> >> wrote: >> >>> On Tue, 22 Mar 2011 10:49:21 -0700, Joerg <invalid@invalid.invalid> >>> wrote: >>> >>>> 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? >>> To be honest, it all depends on the models. Most opamp models don't >>> have those variable set up to tolerance offsets, etc. The AdvAnal >>> models were custom made to be able to add in all those extras, to >>> justify some of the added expense of the option! >>> >>> You can always modify the existing models to add those tolerances. Jim >>> gave you a few clues on how to do that. >>> >>> Charlie >> >> I even sent him a detailed treatise from IntuSoft, but I fear that >> Joerg has no experience rolling his own models. He needs to practice >> up on making subcircuits and behavioral things... hone up his math ;-) >> > >Oh, I've made models in the past. Just not opamps, and not with a >pounding flu-infested head like right now ;-) > > >> I can't even fathom a large enough number to count all the models I've >> made. I'm fond of making my own tool devices... that automatically do >> all the things that LTspice calls up as "Measure"... my tools display >> the results in Probe :-) >> > >Maybe I just place a voltage source in front of every opamp and let it >step the voltage. I can already hear the comments ... "GAAAAAH" ... and >... "EEEUW" ... :-)
Nothing generally wrong with that. But I always have to wonder about designs where +/-7mV VOS would be an issue ;-) ...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 Tue, 22 Mar 2011 12:43:19 -0700, Joerg <invalid@invalid.invalid> > wrote: > >> Jim Thompson wrote: >>> On Tue, 22 Mar 2011 11:58:51 -0700, Charlie E. <edmondson@ieee.org> >>> wrote: >>> >>>> On Tue, 22 Mar 2011 10:49:21 -0700, Joerg <invalid@invalid.invalid> >>>> wrote: >>>> >>>>> 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? >>>> To be honest, it all depends on the models. Most opamp models don't >>>> have those variable set up to tolerance offsets, etc. The AdvAnal >>>> models were custom made to be able to add in all those extras, to >>>> justify some of the added expense of the option! >>>> >>>> You can always modify the existing models to add those tolerances. Jim >>>> gave you a few clues on how to do that. >>>> >>>> Charlie >>> I even sent him a detailed treatise from IntuSoft, but I fear that >>> Joerg has no experience rolling his own models. He needs to practice >>> up on making subcircuits and behavioral things... hone up his math ;-) >>> >> Oh, I've made models in the past. Just not opamps, and not with a >> pounding flu-infested head like right now ;-) >> >> >>> I can't even fathom a large enough number to count all the models I've >>> made. I'm fond of making my own tool devices... that automatically do >>> all the things that LTspice calls up as "Measure"... my tools display >>> the results in Probe :-) >>> >> Maybe I just place a voltage source in front of every opamp and let it >> step the voltage. I can already hear the comments ... "GAAAAAH" ... and >> ... "EEEUW" ... :-) > > Nothing generally wrong with that. But I always have to wonder about > designs where +/-7mV VOS would be an issue ;-) >
I am quite sure it won't be. But the task at hand is to provide proof that it won't be ;-) -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
On Tue, 22 Mar 2011 12:54:35 -0700, Joerg <invalid@invalid.invalid>
wrote:

>Jim Thompson wrote: >> On Tue, 22 Mar 2011 12:43:19 -0700, Joerg <invalid@invalid.invalid> >> wrote: >> >>> Jim Thompson wrote: >>>> On Tue, 22 Mar 2011 11:58:51 -0700, Charlie E. <edmondson@ieee.org> >>>> wrote: >>>> >>>>> On Tue, 22 Mar 2011 10:49:21 -0700, Joerg <invalid@invalid.invalid> >>>>> wrote: >>>>> >>>>>> 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? >>>>> To be honest, it all depends on the models. Most opamp models don't >>>>> have those variable set up to tolerance offsets, etc. The AdvAnal >>>>> models were custom made to be able to add in all those extras, to >>>>> justify some of the added expense of the option! >>>>> >>>>> You can always modify the existing models to add those tolerances. Jim >>>>> gave you a few clues on how to do that. >>>>> >>>>> Charlie >>>> I even sent him a detailed treatise from IntuSoft, but I fear that >>>> Joerg has no experience rolling his own models. He needs to practice >>>> up on making subcircuits and behavioral things... hone up his math ;-) >>>> >>> Oh, I've made models in the past. Just not opamps, and not with a >>> pounding flu-infested head like right now ;-) >>> >>> >>>> I can't even fathom a large enough number to count all the models I've >>>> made. I'm fond of making my own tool devices... that automatically do >>>> all the things that LTspice calls up as "Measure"... my tools display >>>> the results in Probe :-) >>>> >>> Maybe I just place a voltage source in front of every opamp and let it >>> step the voltage. I can already hear the comments ... "GAAAAAH" ... and >>> ... "EEEUW" ... :-) >> >> Nothing generally wrong with that. But I always have to wonder about >> designs where +/-7mV VOS would be an issue ;-) >> > >I am quite sure it won't be. But the task at hand is to provide proof >that it won't be ;-)
Trust me ;-) ...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
On Tue, 22 Mar 2011 12:54:35 -0700, Joerg <invalid@invalid.invalid>
wrote:

>Jim Thompson wrote: >> On Tue, 22 Mar 2011 12:43:19 -0700, Joerg <invalid@invalid.invalid> >> wrote: >> >>> Jim Thompson wrote: >>>> On Tue, 22 Mar 2011 11:58:51 -0700, Charlie E. <edmondson@ieee.org> >>>> wrote: >>>> >>>>> On Tue, 22 Mar 2011 10:49:21 -0700, Joerg <invalid@invalid.invalid> >>>>> wrote: >>>>> >>>>>> 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? >>>>> To be honest, it all depends on the models. Most opamp models don't >>>>> have those variable set up to tolerance offsets, etc. The AdvAnal >>>>> models were custom made to be able to add in all those extras, to >>>>> justify some of the added expense of the option! >>>>> >>>>> You can always modify the existing models to add those tolerances. Jim >>>>> gave you a few clues on how to do that. >>>>> >>>>> Charlie >>>> I even sent him a detailed treatise from IntuSoft, but I fear that >>>> Joerg has no experience rolling his own models. He needs to practice >>>> up on making subcircuits and behavioral things... hone up his math ;-) >>>> >>> Oh, I've made models in the past. Just not opamps, and not with a >>> pounding flu-infested head like right now ;-) >>> >>> >>>> I can't even fathom a large enough number to count all the models I've >>>> made. I'm fond of making my own tool devices... that automatically do >>>> all the things that LTspice calls up as "Measure"... my tools display >>>> the results in Probe :-) >>>> >>> Maybe I just place a voltage source in front of every opamp and let it >>> step the voltage. I can already hear the comments ... "GAAAAAH" ... and >>> ... "EEEUW" ... :-) >> >> Nothing generally wrong with that. But I always have to wonder about >> designs where +/-7mV VOS would be an issue ;-) >> > >I am quite sure it won't be. But the task at hand is to provide proof >that it won't be ;-)
To keep it pretty (and invisible to the client), put the voltage source inside the subcircuit. Parameterize the value of VOS, but do it global so you can manipulate from outside. ...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 Tue, 22 Mar 2011 12:54:35 -0700, Joerg <invalid@invalid.invalid> > wrote: > >> Jim Thompson wrote: >>> On Tue, 22 Mar 2011 12:43:19 -0700, Joerg <invalid@invalid.invalid> >>> wrote: >>> >>>> Jim Thompson wrote: >>>>> On Tue, 22 Mar 2011 11:58:51 -0700, Charlie E. <edmondson@ieee.org> >>>>> wrote: >>>>> >>>>>> On Tue, 22 Mar 2011 10:49:21 -0700, Joerg <invalid@invalid.invalid> >>>>>> wrote: >>>>>> >>>>>>> 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? >>>>>> To be honest, it all depends on the models. Most opamp models don't >>>>>> have those variable set up to tolerance offsets, etc. The AdvAnal >>>>>> models were custom made to be able to add in all those extras, to >>>>>> justify some of the added expense of the option! >>>>>> >>>>>> You can always modify the existing models to add those tolerances. Jim >>>>>> gave you a few clues on how to do that. >>>>>> >>>>>> Charlie >>>>> I even sent him a detailed treatise from IntuSoft, but I fear that >>>>> Joerg has no experience rolling his own models. He needs to practice >>>>> up on making subcircuits and behavioral things... hone up his math ;-) >>>>> >>>> Oh, I've made models in the past. Just not opamps, and not with a >>>> pounding flu-infested head like right now ;-) >>>> >>>> >>>>> I can't even fathom a large enough number to count all the models I've >>>>> made. I'm fond of making my own tool devices... that automatically do >>>>> all the things that LTspice calls up as "Measure"... my tools display >>>>> the results in Probe :-) >>>>> >>>> Maybe I just place a voltage source in front of every opamp and let it >>>> step the voltage. I can already hear the comments ... "GAAAAAH" ... and >>>> ... "EEEUW" ... :-) >>> Nothing generally wrong with that. But I always have to wonder about >>> designs where +/-7mV VOS would be an issue ;-) >>> >> I am quite sure it won't be. But the task at hand is to provide proof >> that it won't be ;-) > > To keep it pretty (and invisible to the client), put the voltage > source inside the subcircuit. Parameterize the value of VOS, but do > it global so you can manipulate from outside. >
It's a design by the client, and they are very professional guys. At the end they should see everything that is in the sims so they can talk it over. I'll probably have to do the params thing on a voltage source or something. But first I want to ask Cadence support whether there isn't a secret hook to unlock the real-world sim. I mean, what's the point of even having an offset in the model (and this one does) when the simulator then blindly takes a 7mV entry as always being +7mV and ignores PTOL and NTOL completely. If you enter -2mV it always calculates with -2mV. To me that makes no sense in a worst case sim. If, as Charlie assumes, this feature is only available by forking over some more bucks then at least PSpice should respond with a stop sign or "not available at this level". -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Jim Thompson wrote:
> On Tue, 22 Mar 2011 10:51:26 -0700, Joerg <invalid@invalid.invalid> > wrote: > >> Charlie E. wrote: >>> On Mon, 21 Mar 2011 16:49:38 -0700, Joerg <invalid@invalid.invalid> >>> wrote: >>> >>>> 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 :-) >>> 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! >>> >> 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. >
Using the roached on voltage sources right now. Found out another thing tho: WC does not like math expressions for the output variable, such as ABS(V(yadayada)). It errors on that. Oh man. Ok, I can make a kludge for that as well but I must say this is all a bit disappointing. Looks like in the end I'll have a sim with two dozen kludges, a couple of car jacks, five shims and 10ft of duct tape. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Joerg wrote:

> Jim Thompson wrote: > >>On Tue, 22 Mar 2011 10:51:26 -0700, Joerg <invalid@invalid.invalid> >>wrote: >> >> >>>Charlie E. wrote: >>> >>>>On Mon, 21 Mar 2011 16:49:38 -0700, Joerg <invalid@invalid.invalid> >>>>wrote: >>>> >>>> >>>>>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 :-) >>>> >>>>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! >>>> >>> >>>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. >> > > > Using the roached on voltage sources right now. Found out another thing > tho: WC does not like math expressions for the output variable, such as > ABS(V(yadayada)). It errors on that. Oh man. Ok, I can make a kludge for > that as well but I must say this is all a bit disappointing. Looks like > in the end I'll have a sim with two dozen kludges, a couple of car > jacks, five shims and 10ft of duct tape. >
Did you try (ABS(V(xxxx))) ? Jamie