[SI-LIST] Re: Via modeling & de-embedding
- From: Ivan Ndip <ndip@xxxxxxxxxxxxxxxxx>
- To: hassan@xxxxxxxx
- Date: Fri, 16 Jul 2004 10:09:32 +0200
Hi Hassan,
How "long enough" must the trace segments be? Do you have any experience
in determining the exact length?
Best regards,
Ivan Ndip
Hassan O. Ali wrote:
>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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