On Wed, 4 Jun 2003 00:32:03 -0400, you wrote:

>Hello all,
>
>I have a project where there is significant digital next to sensitive
>analog (mic preamp) on a small board.  I'd like to put a screen or
>shield of some sort between the two.  There are already separate grounds
>and it is inside a metal box.
>
>I see occasionally in tv sets and the like aluminum (?) shields or
>screens covering a particularly sensitive (or radiating!) sections of
>circuitry.  My question is ... are these available anywhere?  Or are
>they typically something that is made in a metal shop along with
>whatever chassy metalwork that needs to be done?
>
>If I have them made, is any particular types of metal better or worse
>than others?  Right now I'm thinking of just a vertically mounted
>"strip" or "wall", kind of like a tennis net, say, between the two board
>sections.
>
>I'm not 100% sure its necessary, this design is a radical reworking of
>an (aging) existing product, which used two layers, and I'm using four,
>and am getting significantly better performance already.  But if a 25c
>piece of metal can get me another 2db, I'll take it!  Also I have seen
>these screens over crystals/clock gen circuits in other audio A/D
>products and maybe it would help this one too.
>
>I have access to an audio precision 2 (amazing piece of equipment) so a
>does-it-improve-things yes/no test is easy to do.

You can buy off-the -shelf cans from several places, and if you need a =
custom one, Tecan can do
photochemically etched sheets that you fold up into cans for very low =
tooling cost if you design it
yourself.=20

=46or this sort of app however I think you should be able to do without =
with good design practice -
minimising radiation of the digital signals (decoupling, grounding, =
careful routing), and minimising
susceptibility of the analog section (low impedance, clean, independent =
supplies, limiting
bandwidth).
The best bet would probably be to allow for a can in your PCB design, but=
 try to design out the need
for it as much as possible - that way you can choose to fit it or not =
when you have measured the
performance. (Much easier to leave something off a PCB than add it =
later!)

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