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Reply-To: "Fred Bartoli"
From: "Fred Bartoli"
References: <firstname.lastname@example.org> <email@example.com>
Subject: Re: SPICE sources
Date: Sat, 21 Dec 2002 16:31:39 +0100
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NNTP-Posting-Date: 21 Dec 2002 16:30:25 MET
"Paul Burridge" a écrit dans le message news:
> On Sat, 21 Dec 2002 15:45:41 +0100, "Fred Bartoli"
> opined thusly:
> >It seems that there will be much more things that'll baffle you when
> >My advice is that you look for a good Spice starter book. This should
> >lot of things more clear to you, especially the relationship between a
> >circuit or component and the way it's modeled with spice or even
> >for study.
> I've tried, Fred. I was in one of London's largest bookstores only 2
> days ago and only managed to find one title on Spice (which I have
> purchased) but it's not the kind of 'big dummies' guide I really need
> at this stage. I'd still be interested in the answers to the
> questions, though!
I don't know which one you bought but generally all those I found were
pretty basic ones. In fact you'll have to really search to find more
substential ones. I don't have any title to recommand you because I found
pretty bad the ones I found when starting but I'm sure you'll have good
For the sources, there are classical voltage sources (V) and I sources that
have different sets of parameters which one depends on the particular
simulation you want to run. Go to your book for the details then get back if
you need further explanations.
Then there are *controled* sources which are VCVS, VCCS, CCVS, CCCS :
VCVS : voltage controled voltage source i.e. a voltage source who's output
voltage is controled from an *input voltage*. It can be used, for example,
as a *perfect* voltage amplifier block and is often used as a really quick
and really dirty opamp. It is dirty in the sense that it's too much perfect
and forget some basic really important aspects of real opamps.
VCCS : voltage controled *current* source i.e. a voltage source who's
output voltage is controled from an *input current*. It can be used, for
example, as a *perfect* transconductance amplifier block.
CCVS and CCCS are the same as the aboves but their outputs are current
sources instead of voltage sources.
These, and the V and I sources, are almost all the ones built into spice.
All the others (+12V, Vdd, Vcc...) are simply derived from the basic ones
and are only commodities provided in the components library by the vendor
and differ from one spice to another. Mine don't have the fancy AC source
provided with PSpice and I don't really miss them for example.
For the "ground" there's no more "ground" in spice than in the real world.
There are only reference nodes, which are the one you decide to be. It's
just a matter of what you want your voltage reference to be. With Spice you
can make differential measurements like the ones you make with the *two*
probes of your meter which form is V(x,y) and you also have an implicit
measurement, V(x), referenced to the 0 node which is often reffered to as
ground but in fact is not.
I don't know what Spice you're using (but I guess it's PSpice) but my advice
is to *forget* the fancies voltages source, grounds... at least at the
beginning. This is mauch more confusing than helping for the beginner.
So practice with your book and *simple* examples and then, when you'll be
more fluent with spice, you'll decide wheter to use or not these things that
troubles you. Again these are *not* necessary at all.
> "What is now proved was once only imagin'd"
> - William Blake, 1793
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