[sdiy] Analog vs. Digital grounds and Doepfer power bus.

[Rude 66]

michael,

 what a well written explanation. i wasn't even following the thread, but i
learned a few things from this post. as someone with absolutely no talent
for math, physics, or anything like that, i often get very lost very quickly
in electronics theory. throw in more than one variable and my brain starts
circuit bending itself.
it's very hard to find explanations for basic electronic 'things' that are
both not too dumb, and still understandable for someone like me.

this was one of them..;-)

ruud



----- Original Message -----
From: "Michael Baxter" <mab at cruzio.com>
To: "Bret Truchan" <clone45 at hotmail.com>
Cc: <synth-diy at dropmix.xs4all.nl>
Sent: Wednesday, November 26, 2003 1:09 AM
Subject: Re: [sdiy] Analog vs. Digital grounds and Doepfer power bus.


> Hi Bret,
>
> I'll try to explain analog vs. digital grounds, but not the Doepfer power
> bus, which I have no experience with.
>
> The main issue with ground is that for every power supply voltage that
> sources current I to circuitry, there is a return current I' that goes
> back to the power supply, from somewhere, typically a ground bus.
>
> This is true for both digital and analog circuits. In the case of digital
> circuits, very often the current being drawn and returned is impulsive --
> it's needed very quickly (in say 1-100 nS, depending on the circuitry) in
> order to raise or lower a voltage step somewhere in the system. In digital
> circuits, there's a lot of this going on concurrently, making it an
> impulsive or "spikey" electronic noise environment.
>
> If there are not good return paths to ground for these currents, they will
> "leak" or "contaminate" other circuitry, particularly for example
> sensitive analog circuits that utilize current on a continuous or "AC"
> basis, but perhaps at very low level (.1 - 100 uA or so).
>
> The contamination occurs because current always follows the path of least
> resistance. In a well-designed system, this is a the ground return path.
>
> A good strategy for minimizing impulsive noise interactions between
> digital and analog circuits is in fact to use separate ground returns.
>
> These will meet at the point of least resistance (or impedance, in terms
> of AC, or high frequency use of current): the power supply ground, quite
> close to the power supply.
>
> A wholy plausible scenario in a synthesizer is there are +12V or +15V and
> -12V and -15V supplies for linear or analog circuitry, and a +5V supply
> for digital circuitry -- so, three grounds, one for each supply voltage.
>
> Hope this is a helpful explanation!
>
> Best,
> Michael
>
> On Tue, 25 Nov 2003, Bret Truchan wrote:
>
> >
> > Hello!
> >
> > I love this forum!  I'm a little confused.  I've been told that it's a
good
> > idea to keep ICs grounds and analog grounds separate.  When I look at my
> > Doepfer power bus, it has three grounds.  Do the Doepfer modules utilize
the
> > different grounds to keep their analog and digital ground separate?  If
so,
> > how do you know which one to use for what?
> >
> > Or, are the three grounds on the power bus tied together?
> >
> > Thanks!
> > - Bret
> >
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