component layouts?

[Ian Fritz]

Good suggestions from Jules and Jim. I would add a suggestion from recent
experiences I have had working on VCO design -- include lots of ferrite
beads on the power supply lines. I divided the circuit into several circuit
blocks and ran separate power lines for each section through ferrite beads
back to a common supply input. This is the first time I have been able to
virtually eliminate switching spikes from showing up in the expo converter,
etc. This may be overkill for many applications, of course, but for critical
circuits with wide ranging voltages it really works well. It has a big
advantage over the usual technique of adding series decoupling resistors in
that the supply remains "hard" at dc, in other words, there is no shift in
supply voltage as the load current varies.

  Ian


----- Original Message -----
From: "Jules Ryckebusch" <ryckebu at ersg.san.mrms.navy.mil>
To: "Jim Patchell" <patchell at silcom.com>
Cc: "zapsn0n" <n0nspaz at loa.com>; <synth-diy at node12b53.a2000.nl>
Sent: Tuesday, September 26, 2000 2:02 PM
Subject: Re: component layouts?


> Ohhh Doggie! Compnent layout grounding and bypassing is always an art
kinda
> thing. There are some good downloadable things on it from Analog Devices
web
> site in their ap notes. I have found that grounding is usually the cuplrit
in
> most cross talk issues but being neat counts the most. I usually build
"one
> of's" that are bread boarded. I keep the power supply leads as short as
> possible and bypass all IC's at the pins with a 10-47uf electrolytic and a
.1uf
> poly or ceramic cap too. On a couple occasions (Power amplifiers) I have
found
> the need to add additional bypass caps with in the circuit in places where
a
> current sink/source that was stable was needed. Another helpful thing is
to
> mount the PC board close to a ground plane. ie metal chassis of case etc.
>
> Jules Ryckebusch
>
> Jim Patchell wrote:
>
> >     Boy, talk about opening a can of worms.....
> >
> >     Bypassing is both art and science.  My rule of thumb 1st of all, 1
> > bypass cap, to ground, for each power supply pin.  There are exceptions
to
> > that rule of thumb, but that is another story.  It is also best to keep
the
> > distance between the bypass cap and the power supply pins as short as
> > posible.  The idea of the bypass cap is to provide current for those
peak
> > useage times.  For analog sutff, this is not quite as critical as for
high
> > frequency switching, but the idea is still the same.
> >
> >     Another general rule, I cannot think of a case where it is posible
to
> > have too much bypassing.
> >
> >     Now, cross talk is another problem.  Even with good bypassing, you
are
> > going to want to look at the circuit and ask, where can extraneous
signals
> > get into things.
> >
> >     In conclusion, all I can say is that this is a pretty big subject.
I
> > don't know of any articles on the net that cover this.  You will
probably
> > get enough replys to make an article though1 :-)
> >
> >     -Jim
> >
> > zapsn0n wrote:
> >
> > > hi all,
> > >
> > > can anyone point me to some general online info & tips on component
> > > layouts, e.g. the placement of capacitors on DIY circuit boards to
avoid
> > > crosstalk, etc etc  ?
> > >
> > > thanks,
> > > mark scetta
>
>