[SI-LIST] Re: Shield ground isolation

Paul,

I think Dr. Johnson answered this already.

I think the real question is how to prevent high speed currents from 
flowing in large area loops.  Shields are the last shunt path for fields 
that would otherwise radiate into a victim antenna somewhere.

The idea is to limit the amount of energy a shield needs to shunt, not 
restrict its ability to provide the shunt.   If you intentionally insert HF 
isolation, you will limit the shield's ability to do its job.


Regards,


Steve.
At 08:51 AM 2/24/2003 +0800, Paul Young wrote:

>Hi,
>
>Same to me.
>
>Can anyone out there give the answer?
>
>Paul
>----- Original Message -----
>From: "Kuriakose, Anand" <Anand.Kuriakose@xxxxxxx>
>To: <si-list@xxxxxxxxxxxxx>
>Sent: Sunday, February 23, 2003 1:07 AM
>Subject: [SI-LIST] Shield ground isolation
>
>
> >
> > Hi All,
> >
> > On high speed boards with I/O connections running to outside world, the
> > shield ground of the connectors should be isolated from the digital ground
> > if the board has to meet the requirements of EMI/EMC compliance standards.
> >
> > Are there any side-effects of isolating the shield ground from the digital
> > ground?
> >
> >
> > I have seen on some boards, that the isolation is achieved by using
>ferrite
> > beads. On few others i have seen capacitors being used b/n shield and
> > digital ground.
> >
> > How are capacitors useful in acheiving isolation? Or are these caps used
>for
> > some other purpose, which i am not able to understand?
> >
> > What is the best method to achieve this isolation?
> >
> > Thanks in advance.
> >
> > Regards,
> > Anand.
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>
>
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