[sdiy] More ground questions

[Scott Stites]

Hi all,
I'm out of town right now, and only have access to my
email if my wife hasn't downloaded it first - otherwise
I have to wait a couple of weeks when I get back to see
it.  I appreciate this discussion immensely. 

Now, this may be the stupid question of the week, but I
was wondering - if I had bypass caps on the module PCB
itself only from the two supply lines to 'clean'
ground, with no bypass cap between the supply lines and
the 'dirty' ground, would I be asking for trouble?

Scott, cooling his heels in a place much colder than
Kansas.

On Sun, 04 August 2002, Ingo Debus wrote:


> 
> harry wrote:
>  > Hi Ingo...
>  >
>  > I either don't understand (or don't agree
with..)
> you.
>  >
>  > If the grounds are separate... AC currents from
> dirty signals bypassed
>  > to the dirty ground... MUST flow in the dirty
ground
> all the way 
> back to
>  > the common ground point.
>  >
>  > This is presumably the lowest impedance point
of the
> power supply 
> system...
>  >
>  > These currents do not flow in the clean ground,
> ever... so they 
> cannot cause
>  > voltage drops and therfore noise in the clean
ground.
>  >
>  > I'm also presuming that the positive and
negative
> power supply 
> leads are separate
>  > as well.
> 
> Yes, if there are separate supply lines for dirty and
> clean circuitry,
> then separate ground lines make sense.
> 
> But in the original mail "four pin connector
cables"
> were mentioned,
> as I understand it, one for clean ground, one for
dirty
> ground, one
> for positive and one for negative supply. No separate
> dirty and clean
> supply lines.
> 
> If there are bypass caps across both the dirty and the
> clean loads
> these two caps (in series, with the supply line in the
> middle) will
> short both ground lines together.
> 
> Ingo

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