[sdiy] spice flamewars, Bob Pease vs Barrie Gilbert

[harrybissell]

Hi KD

this was on a private mailing. I was included because I was one of the
'semi-defenders' of Spice.  I realize that it CAN lie, and is a really
poor
substitute for knowledge of REAL WORLD behavior... but I often simulate
circuits before building to get an idea if I have made any obvious
mistakes...
ie. mistakes that will be REALLY obvious once I breadboard

H^) harry

karl dalen wrote:

> Splendid!
> On wich email list did this argumenting take place?
>
> Reg
> KD
>
>  --- Harry Bissell Jr <harrybissell at prodigy.net> skrev:
> > sorry this is so long... I cut out a lot of the
> > headers to make it more readable and to protect the
> > innocent from exposing their e-mail addys.
> > Thought a lot of folks would get a kick out of it.
> > I wrote to say that Spice has its place, once you KNOW
> > when it is or is not lying.  thread follows H^) harry
> >
> >  From: Ward Silver
> >        Subject: Re: ALLEGED solutions with SPICE...
> >
> >     The issue of SPICE lying or not lying reminds me
> > of Steven Hawking's quote that, "God may not play dice
> > with the Universe, but sometimes he throws them where
> > you can't see them."
> >
> >     Having worked with a fair number of students and
> > young engineers over the years, I can tell you that
> > any simulation at all is dangerously addictive to
> > them.  They have absolutely no clue what the pitfalls
> > are, what the symptoms of breakdown are, or even how
> > to open the hood and really look at the data.  It's
> > treated like a "magic box" in many cases.
> > Furthermore, since very few of them are experienced
> > builders, they will make things in ways that SPICE
> > assumes they won't and shouldn't.  And that more
> > experienced engineers don't.
> >
> >     It's like giving a brand-new driver the keys to a
> > stock car.  EVENTUALLY, they may figure it out, but
> > only after a lot of grief and after someone older and
> > wiser takes them in hand.  It shouldn't have to be
> > that way at all, but...
> >
> >     1) SPICE (standing for simulation in general) is
> > introduced too early and with too few cautions in the
> > engineering curriculum, often in substitution for lab
> > work.  This is BAD JUJU and leads to violations of
> > Will Roger's First Law - "It's not what you don't
> > know, it's what you know that ain't so."  Simulation
> > should be done only in parallel with hands-on lab work
> > and not in substitution for it except in rare
> > circumstances.
> >
> >     2) There is effectively zero emphasis on the
> > simulate-build-compare cycle that shows them how the
> > tool's version of reality differs from what the real
> > electrons are doing.  Without that feedback, they
> > don't learn when the simulation is getting into deep
> > water.  Frankly, I think an entire quarter-long course
> > should be devoted solely to use and misuse of
> > simulation tools.
> >
> >     3) High-speed stuff - anything over a few MHz - is
> > really dangerous in the hands of inexperienced folks.
> > Until they get to senior-level courses, if at all, the
> > subjects of parasitic reactances, transmission line
> > effects, crosstalk, EMC, and other important are not
> > covered.  Yet, they use models that cheerfully support
> > frequencies into the GHz.  It's hard to explain to
> > them why all that stuff in the VHF spectrum is really
> > fiction.
> >
> >     It's nuts that we give this powerful, but
> > sensitive, tool to these young engineers with as
> > little guidance and caution as we do.  Both industry
> > and academia need to work harder on dealing with this
> > problem.
> >
> >     Regards,
> >
> >     Ward Silver
> >
> >
> >             From: Paul Rako
> >
> >         Subject: Re: ALLEGED solutions with SPICE...
> >
> >
> >         Hmmm-- looks like we have a good fight on our
> > hands here.  I used to try and get between combatants
> > and say "calm down", but today I am bored and so I say
> > to both these esteemed gentleman--- are you going to
> > take that shit from HIM???!!?!?!?!?!
> >
> >         Ha ha ha--
> >
> >         OK, on a more level keel-- I can offer a few
> > observations.  First it is not surprising to me, an
> > application engineer, that Mr Gilbert thinks that
> > SPICE is just dandy.  Most IC guys do.  If you live in
> > the transistor design world and have 10 to 50 million
> > a year to feed both a Process and Modeling and CAD
> > (sorry for the redundant "and" Barrie) yes, SPICE can
> > give you a first-order indication of how an IC will
> > work.  However, for us board-level guys-- SPICE is a
> > lot less useful and a lot more dangerous.  At high
> > speeds the board is a pretty important component and
> > unless you drop the 30 grand for hyperlynx you can't
> > factor the board's effect into the design on a
> > computer.
> >
> >         I am also amazed that Analog Devices does not
> > have any trouble with their models-- not even on new
> > processes?  I have seen even our huge-dollar IC spice
> > tell lies on a new process.  Sure it gets worked out
> > but that can often take a couple of spins and that is
> > big time and big money.  And the errors in SPICE are
> > most often in the very same corner cases where Mr.
> > GIlbert brags that SPICE does so well, over
> > temperature and process and time.
> >
> >         If you want to be a software engineer I think
> > that is a fine and honorable profession but I, like
> > Mr. Pease, continue to be disturbed by this modern
> > effete tendency by EEs to think that their job is to
> > sit at a workstation all day playing with a computer.
> > Then they toss the design over a wall to another
> > clueless geek that does the layout.  Then everybody is
> > so surprised and blame the "tools" when the dang thing
> > doesn't work.  "It can't be us-- were are so smart we
> > never make mistakes"-- right.  It did work on the
> > screen after all.
> >
> >         I also tend to dispute Mr. Gilbert's dismissal
> > of prototyping as to being a valuable contribution in
> > the design process.  Very smart people seem to have a
> > hard time understanding that they are not being paid
> > to learn-- they are being paid to teach-- teach those
> > nice people in manufacturing how to make a few million
> > of whatever we make so any of us can get paid.  The
> > goal is to get into a real physical piece of green
> > plastic or shiny silicon that can go into production.
> > Worshiping SPICE keeps it in that computer screen
> > phase for the majority of the development and then the
> > "genius designers" can blame layout or the tools or
> > something and all that happens is another 6 months
> > gets added to the design cycle.  After working twenty
> > years as a consultant I can assure everyone that the
> > businessmen that pay the bills are lot happier to see
> > a air-ball prototype that works but has problems
> > rather then some computer print! out that shows what a
> > rosy world we live in.  At least you can put the
> > air-ball into a pretty box and make the show in
> > Chicago.  That screen is not reality-- it is a
> > dangerous drug and although a little can ease your
> > pain, a lot of SPICE and you will just be a junky with
> > your eyes glazed over staring into the screen and no
> > sense of what you are really trying to do-- like
> > getting real hardware going out the door.
> >
> >         Now Bob does like to get on his high horse
> > about SPICE,  but you have to understand any good
> > preacher really can't go soft on the devil and keep
> > the faithful from harm.  I have seen him advise young
> > engineers on how to mix SPICE with a few real-worlds
> > tests-- maybe those air-balls dead-bugged on a board,
> > and then from that see where SPICE lies (and it lies
> > by definition-- as my Professor once said--
> > "everything is based on linear analysis but even a
> > resistor goes nonlinear when you put enough juice in
> > it to melt it").  Then it is time for breadboards--
> > real green plastic boards with real black plastic
> > chips and you still have to count on three spins to
> > get everything right.
> >
> >         Sure SPICE is great-- when the box is small
> > enough.  How appropriate that in college we called the
> > vectors and matrix classes "boxes and arrows".  Yup,
> > that matrix is only right in a very narrow regime--
> > with very good models and proven processes and perfect
> > design rules and a manufacturing operation at 6-sigma
> > and on and on and on- yup-- SPICE works just fine.
> > But in the real analog world SPICE is doing a lot of
> > damage-- not only to budgets but to impressionable
> > young minds.   And if your company is making optimum
> > use of it's resouces the processes are new and models
> > imperfect and the manufacturing is good-enough, not
> > perfect.
> >
> >         So I guess I would have to say that we
> > shouldn't hold a digital opinion in an analog world--
> > yeah, Bob does rant about SPICE but he understands in
> > can teach a few things, especially to idiots like me.
> > But the more experienced you get you may now where to
> > distrust SPICE, as Mr. Gilbert so well demonstrates.
> > I maintain that an Israeli commando with a slingshot
> > will be more effective thane a Boy Scout with an Uzi.
> > I suspect Bob sees indiscriminate SPICE use as
> > analogous to giving Boy Scouts Uzis.
> >
> >         I just did a PSPICE simulation of our very
> > fast LMH6624 used as a trans-impedance amp.  I
> > integrate the output with another LMH6624 and feed
> > that back to the "+" pin of the main amp to servo out
> > the DC.  It simulates just fine.  But all my
> > experience tells me "DANGER WILL ROBINSON".  I know
> > fast amps just don't like getting hooked tail-to-nose
> > like this.  I will build it and report if the real
> > circuit works or not.
> >
> >         Paul
> >
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