[SI-LIST] Re: Via modeling & de-embedding
- From: "Hassan O. Ali" <hassan@xxxxxxxx>
- To: David Siadat <dsiadat@xxxxxxxxx>
- Date: Thu, 15 Jul 2004 15:05:26 -0400 (EDT)
It seems that "de-embedding" in this thread has been used to suggest that one
can create
an "isolated" via model that can be used in various other environments such as
with
different trace widths and thicknesses; different signal rates, etc. If that is
the
case, then I think that suggestion is not accurate enough.
I tend to believe that via characteristics (hence its model) cannot be isolated
from the
surrounding environments - especially for higher frequencies. The trace/via-pad
transition itself presents a discontinuity that contributes to the parasitics
of the
via. The pads have their own parasitics. Neighboring ground/power vias also can
influence the signal via performance. All of those along with the via barrel
parasitics
contribute to the overall via characteristics and have to be appropriately
considered in
model creation.
As to de-embedding, I think you won't get accurate results if your reference
(de-
embedding) plane is right at the transition. In other words, an accurate via
model
should include trace segments long enough to ensure that the field at the
segment ends
are mainly of the dominant mode of field propagation. In fact most (if not all)
de-
embedding techniques make that assumption.
Regards.
Hassan.
On Jul 15, David Siadat <dsiadat@xxxxxxxxx> wrote:
>
> Hello Ivan,
>
> De-embedding the transmission line feeding the via is limited to the
> edge of the anti-pad region that the transmission line is referenced to.
> That could mean an additional 17.5 mil transmission line for 35mil diameter
> anti-pad. The inductance value of this transmission line can be significant
> compare with the inductance of the via itself.
>
> Regards,
> David
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