Monte Carlo analysis is a very good use of spice tools. You have the 
components in the design vary by the tolerance amounts based on 
probabilities and run many simulations to see the distribution of the final 
product output to see what percentage fall outside of the product limits. 
Often you can simplify the circuit and take a yield loss while still 
maximizing profit because of a reduction in component cost. The down side 
is there is still a possibility that all the parts come in skewed to the 
worse case and your yield is zero.
I have used this technique in the past very successfully with PSPICE and 
ISPICE but have never used the Protel simulator yet.


At 07:11 PM 6/30/02 +0200, you wrote:
>That has nothing to do with circuit simulation.
>You were just joking, right ?
>
>Rolf Molitor
>Ing.Buero i2e
>Remscheid / Germany
>
>-----Ursprüngliche Nachricht-----
>Von: "Georg Beckmann" <[EMAIL PROTECTED]>
>An: "'Protel EDA Forum'" <[EMAIL PROTECTED]>
>Gesendet: Samstag, 29. Juni 2002 14:25
>Betreff: [PEDA] AW: SPICE sim question
>
>
> > Hi Gary,
> >
> > I want to use the simulator for a Monte carlo analyse for the following
> > question.
> > To simplify what I mean is, imagine a bridge circuit with four resistors
>of
> > 1% tolerance.
> > The circuit is usable, if the bridge - voltage is below a certain limit.
>How
> > many
> > percent of my circuits are usable so that I can decide what's cheaper, to
> > throw away
> > the bad samples or use of more expensive resistors.
> >
> > Do you know how this is done ?
> > When I looked at the examples, they only calculated the worst case of a
> > circuit, but
> > that's not the question, I want to get the distribution of a parameter.
> >
> > Georg
> >
> >
> > Afshin Salehi wrote:
> > >
> > > Just out of curiosity, what types of things do you guys run simulations
> > on?
> >
> > Amplifiers, linear and switching power supplies, filters, and just about
> > anything else that will need tweaking on the bench.
> >
> > > What drives you to run a simulation on that specific device?
> >
> > Testing for stability, what range of component values (tolerance) will
> > work reliably, gain, rolloff, keeping signal levels away from the rails
> > when designing high gain multi-stage amplifiers, and most important of
> > all, gaining rapid insight into what happens when you go outside the
> > box.  Also, nothing catches fire or explodes in a simulator!
> >
> > >How accurate is the simulation to a real world bread boarded device?
> > >
> > Once you learn how to use simulation I would say about 98% accurate, but
> > there is a giant proviso here, you must have accurate models and you
> > must understand the limitations of the simulation process.  I cannot
> > remember the last time a finished product did not behave as the
> > simulation did.  The more often you simulate, the better you and your
> > results get.
> >
> > > Jon Elson said it takes a day at first then maybe an hour or so each
>time
> > to
> > > remember things, how is that justified to your boss?  I am really just
> > > curious as to what things people run sims on, how complex those circuits
> > > that are simulated are, and if the tests are worth while?
> > >
> > I use an old but very capable DOS version ($15,000 when new) of PSPICE.
> > I can hand type an ASCII circuit description page in about a half-hour
> > (three or four op-amps and twenty or thirty passive parts).  Another
> > twenty minutes to patch typos and missed connections. After the circuit
> > is running you can do a number of tests in minutes that would take a
> > week on the bench.  Whether it is worth the trouble or not all depends
> > on what you're doing.  The last thing I did was a strain gauge amplifier
> > (something I never did before).  Had the circuit up and running in one
> > afternoon, cost of components about $10 versus a packaged product with
> > similar specs from Omega for $400.  Is that worthwhile?  My boss thought
> > so.
> >
> > It all depends...
> > Gary Packman
> >
> > > Thanks,
> > >
> > > Afshin
> > >
> > > ************************************************************************
> > > * Tracking #: 089C581B73790B40A34A5F9530FFA0A756B58F96
> > > *
> > > ************************************************************************

Larry G. Nelson Sr.
mailto:[EMAIL PROTECTED]
http://www.ultranet.com/~nr


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