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'16c62a'
1997\12\08@175601 by engelec

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Hi to all engineers.

I just noticed that 16c62a has 2 grounds. what is the purpose of this?


Andre








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1997\12\08@205831 by Martin McCormick

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Just as the model for a power source is a constant voltage source of 0
Ohms in series with some arbitrary value of resistance that is determined by
the makup of the materials in the power supply, a ground can be thought of
as having some resistance hidden away in the resistance of the materials that
make up the circuit.  Since resistors in parallel produce a R(total) that is
less than either of the resistances by themselves, having more than one
ground insures that there will be less possibility for crosstalk between
signals caused by ground loops.  If one ground is good, two are better.

       Circuits that are sensitive to noise such as audio amplifiers and
A/D converters will malfunction if there are ground loops and digital circuits
will even malfunction if the ground loops are bad enough.

       I am not an engineer, but it is safe to say that decoupling of
switching transients is one of the best things that one can do to make a
circuit work as planned and not glitch at the worst time.

Martin McCormick WB5AGZ  Stillwater, OK 36.7N97.4W
OSU Center for Computing and Information Services Data Communications Group

Andre Abelian writes:
>Hi to all engineers.
>
>I just noticed that 16c62a has 2 grounds. what is the purpose of this?

1997\12\20@132331 by Krishna Murphy

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On Dec. 8, Martin McCormick wrote:
> having more than one ground insures that there will be less
> possibility for crosstalk between signals caused by ground loops.
> If one ground is good, two are better.

Dear Martin:

More is not always better! (Ask the friends of Bill W.)

Seriously, I have had a number of experiences with ground loops, and
they are invariably caused by exactly what you are describing as
desirable. In certain carefully controlled cases where packaging or
other constraints force it, multiple ground current paths can be
tolerated since not having them is worse. This does not apply to
situations where there are functionally separate circuits in the same
chip or package (probably what is happening here.)

The basic rules are: use only a single point ground, use a heavy enough
conductor to keep the current-induced voltages low, and *do* separate
the sensitive stuff from the heavy power stuff.

Since the C62 datasheet is a 20-minute download, I'll just be guessing
that they are separating the high current drivers from the more
sensitive circuitry. You might very well gain an advantage (in
reliability, if nothing else) by keeping them separate out to the power
connector of your cktbd, which should be the "single point" as far as
the board's concerned.

Regards, Kris Murphy
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