Mira,

The few good designers I have know in my 25 years of design *always*
simulate their designs.  Engineers who cannot design a functioning
product without a simulator shouldn't be engineers in the first place. 
However, every engineer that takes simulation seriously can *improve*
any design with simulation. I don't consider simulation a debug tool,
rather an optimizing tool.   Have you ever purchased a bad piece of
electronic equipment. If yes, this underscores the importance of
simulation.  If no, you have had the good fortune of purchasing gear
that probably received a thorough regimen of simulation before going
into production.  Do you think that camcorder you take so much for
granted just fell out of somebody's schematic generating package onto
the production line?  People who argue that simulation takes too much
time to be worthwhile are, in my experience, not proficient at
simulation.  It takes me less time to simulate a circuit than it takes
to fill out the purchase orders for the parts that go into the
prototypes.  It does takes time to become proficient and you need tools
that are easy to use.  Pspice is easy, Protel is not (probably because I
haven't taken the time to learn properly, I already know PSPICE so why
bother with Protel). Also, with more experience you learn to recognize
which portions of a circuit actually merit simulation.  Voltage
dividers, not necessary. High-gain multi-stage process control
amplifiers that must operate in a plus or minus 100 degree temperature
environment, a must.

Gary Packman

Mira wrote:
> 
> Nice and true thoughts, Gary.
> It all depends on:
> 1. How experienced you are when doing and debugging
> your designs.

Absolutely.
 
> 2. How experienced you are with the simulation tools.
> Mainly analog specialists go for this.

Digital state machines should always be simulated.
Software is always simulated before being released. Try to imagine how
bad Windows would be without simulation. DOS 3.1 would still be on the
drawing board.

> Good designers rarely simulate their circuitry, while
> newbies start with it to see the effect of changing
> the circuitry and the values.

Good designers don't need to simulate to verify their designs.
The BEST designers always simulate to improve their already good
product.

> 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.

If the simulation is done well, there is no debugging.  I never have to
do any debugging (with the routine exception of software).

Gary Packman

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