Good designers rarely simulate their circuitry???
Perhaps 20 years on I am still a newbie!
I find simulation a great tool checking stability of control loops,
finding the optimum resistor for damping, finding out the effect of
parasitic inductance and capacitance, calculating noise gain of
preamps... I rarely build a lashed up prototype these days. Its not
usually possible anyway as everything needs a ground plane and
components are too small to modify easily!
If you find simulations taking you too long, get some training to use
them better. I can simulate things between about 10 and 100 times
faster than building them, and they don't catch fire (important for
power supply work). They have to be built in the end but my
understanding is usually much better than if I had just done a rough
design and built it.
Cheers, Hugh.
-Original Message-
From: Mira [mailto:[EMAIL PROTECTED]]
Sent: Sunday, June 30, 2002 10:11 AM
To: Protel EDA Forum
Subject: Re: [PEDA] SPICE sim question
Nice and true thoughts, Gary.
It all depends on:
1. How experienced you are when doing and debugging
your designs.
2. How experienced you are with the simulation tools.
Mainly analog specialists go for this.
Good designers rarely simulate their circuitry, while
newbies start with it to see the effect of changing
the circuitry and the values.
As opposed to what was already said, I can say that
simulations cannot replace the real world. They are
helpful, yes, but only if you know what you are doing. Otherwise they
may put you in a wrong direction. As for the time you'll need to do this
job... it depends on you. I've seen people spending months for
simulations and then twice more time for debugging.
Luckily there are still bosses, who may afford to pay
for it.
Mira
--- Gary Packman [EMAIL PROTECTED] wrote:
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
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