[sdiy] Isolating a +-15v/+5v PSU?

[John Luciani]

On 7/27/06, Jeff Farr <moogah at gmail.com> wrote:

> Any other tips?
>
> So, how much do I stand to gain by creating a grounding
> tree in the analog section?

Rather than slicing up your ground plane (and increasing its impedance) you may
be better off with one large plane (the let ground abound philosophy). There is
a FAQ from National Semiconductor at

   www.national.com/appinfo/adc/files/questweb_dec_2001.pdf

Place your 0.1uF caps very close to each chip (underneath can usually
work nicely)
to provide local filtering. You want to keep the loop area small when connecting
these caps. Place your larger filter caps at the linear regulator.

To confirm that your filtering is working add a few test points.
To measure noise I usually place a coax jack on my vector board or
PCB. The jacks I use are made my Johnson and the part numbers are
129-0701-301 (horizontal) and 129-0701-201(vertical). Both are
available from Digikey. This will allow you to do your noise
measurements without the ground lead of your probe. You may want to
verify the size of your probe sleeve before you order. I seem to
recall Tek probes coming in multiple sizes. Always seemed to be the
wrong size for the adapter on my board ;-)

On boards where I could not place an RF jack I try to place two Vector
pins (K24A) spaced so that the ground sleeve of the probe would rest
against one and the tip would rest against the other.

(* jcl *)

-- 
http://www.luciani.org