[SI-LIST] Re: Different types of Critical Net Shilding
- From: "Neeraj Pendse" <cnepsc@xxxxxxxxxxx>
- To: nareshv_63@xxxxxxxxx
- Date: Wed, 17 Dec 2003 16:00:57 -0800
Hi Naresh,
A *return path* is a good shield. Anything else is either a bad shield
or not a shield at all. So whether it's good to VCC or VSS depends upon
what is the return path of the signal. If the "shield" conductor does
not form part of return path, then I am doubtful in its effectiveness as
a shield.
Note that adding return paths will change the characteristic impedance
of the signal line, so you have to take that into account.
A basic thing is to have the "shield" connected to both ends and then
determine if return current flows in it. If it doesn't, then the
"shield" is not doing you any good.
I hope that answers your question.
- Neeraj.
naresh vijay wrote:
> A Very Basic question?
>
> What is the diffrence between following three cases.
>
> 1. net shielded on both side by Ground(VSS)
>
> 2. net shielded on both sides by supply(VCC)
>
> 3. net shielded on one side by VCC and other side by
> VSS.
>
> 4. net not at all shielded but have wider spacing in
> its surrounding (equivalent to above cases in width
> perspective).
>
> and how these cases affect the efective resistance and
> capacitance values of the net.
>
> expert response to these questions are highly
> appriciated.
>
> Thanks in advance.
> Naresh
>
> =====
> Naresh K. Vijay
> Sr. Design Engineer
> naresh.k.vijay@xxxxxxxxx
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