[SI-LIST] Re: EMC
- From: "Michael E. Vrbanac" <vrbanacm@xxxxxxxxxx>
- To: ivor@xxxxxxxxxxx
- Date: Wed, 05 Nov 2003 16:35:39 -0600
Ivor,
In the simulations I've done, adequately spacing (in x, y, & z directions)
your traces from the ground fills should allow you to avoid affecting the
impedance of your signal traces. What is "adequate" depends on how
much impedance variance you are willing to accept for the type of signaling
you want to do. The more spacing, the less Z variance and vice versa.
For my work, I usually start with about several times the trace height from
the
nearest plane. However, depending on what I am trying to do, I may use many
different spacings. You might need more or less depending on what you are
trying
to do and what you can (or need to) get away with. Try simulating it for
yourself
and see what will work for your application.
Regards,
Michael E. Vrbanac
At 01:44 PM 11/5/2003 -0800, Ivor Bowden wrote:
>I do ground fills on inner layers for some of the reasons already
>mentioned. I wonder how concerned should I be about the signal impedance
> variation this results in. e.g. in a 6 layer stackup S-P-S-S-P-S where
> the inner signal layers are ground flooded, there will be effectively
>3 scenarios: P-S-S-P, P-S-P-P, and P-S-x-P (where x is no copper). Of
>course I will try to have the signals orthogonal in the case of P-S-S-P
> to reduce crosstalk, but every time a signal transitions between the
>cases there will be an impedance change. When is this worth being
>concerned about?
>
>
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