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Subject: Re: Ground loops?
Date: Fri, 13 Sep 2002 22:19:25 +0100
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"Christopher R. Carlen" wrote in message
> markp wrote:
> > Say I had three printed circuit boards. Each board requires a +5V supply
> > ground, and in addition the boards are inter-connected via ribbon cables
> > using separate cables. Let's say the environment is a little noisy from
> > electrical point of view, so the ribbon cables use the every second
> > conductor is grounded type construction.
> > First, what is the best way to connect power? My instinctive reation to
> > is star ground where each card's ground goes to a common point.
> > for the +5V.
> > Second, should the grounds on the ribbon cable connectors be grounded on
> > both ends? Again my reaction is grounding at both ends creates ground
> > that could pick up noise from the environment. My feeling is that only
> > end of the connectors chould be grounded and the other ends left
> > Any views?
> > Thanks.
> > Mark.
> Ground at both ends. That way, the return currents flow adjacent to the
> conductors. That way you both radiate less noise and also, the loop
> area that picks up induced noise from ambient EM fields is minimized.
> If you have conductors carrying signal and the grounds are connected at
> only one end, this may help reduce crosstalk some (grounding both ends
> should be better here too), but the return currents have to flow
> somewhere, that means somewhere you have connected the grounds of both
> boards together. If this is on a different cable than the ribbon that
> we are talking about, then your ground wire and signal wires form a much
> larger area to intersect with ambient fields.
> See what I mean?
> This is one aspect of the problem, that of ambient noise field pickup.
> Another issue is the sort of "ground loop" formed by large currents
> flowing through ground connections, causing a voltage drop across the
> ground bus. Then circuits at one end of the bus incur offset errors
> relative to the other end of the bus, or AC components dropping across
> the ground bus can get injected into low level circuits. It is for this
> issue that the star grounding topology might be appropriate.
> Are you strictly digital here or analog, or mixed?
Oops, I posted this quickly and without thinking! For some reason I forgot
completely about the return currents... I'm not sure what planet I was on
when I asked this, thanks! This is a mixed system with one of the boards
Please everyone, this was an aberration on my part, no need to answer!
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