[SI-LIST] Re: Via modeling & de-embedding
- From: "giancarlo guida" <gguida@xxxxxxxxxx>
- To: <ndip@xxxxxxxxxxxxxxxxx>, <hassan@xxxxxxxx>
- Date: Fri, 16 Jul 2004 11:09:22 +0200
Hi Ivan,
strictly speaking the lenght must be enough to have the
high order mode generated by the discontinuity to die
befor to reach the port.
If you are using HFSS you could use assign
2 or more mode and solve for the port only
you will get the attenuation constant, from that value you could calculate
the exact lenght
In practice a value aroun lambda/10 should be enough.
But I want stress another point, some one focus the attention on the
fact that it seems you are looking for a model for the VIA it self
to be reused in your simulation any time you use the VIA.
While this could be reasonable in low speed application
it could represent only a rough approssimation in High speed.
A VIA is not alone in the pcb and you have to take in to account
the pad, antipad and stub and in any case you need to arrive to the via
and exit from the via.
if I were incharged to get a model for via, I would create an HFSS model,
perform a parametric analysis of the via, including pad, antipad, stub and
line to and from the via
nad then I would pass all the parametric analisys to Ansoft Designer.
I would add the rest of the layout and the driver/receiver model and perform
a parametric circuit simulation in time domain to see the real effect of the
change in the via geometry
I do not want make an advertisiment but I work for Ansoft and I only know
what you could do in Ansoft worl without pretending that Ansoft is the best
tool in the history, please accept my apologies for this
----- Original Message -----
From: "Ivan Ndip" <ndip@xxxxxxxxxxxxxxxxx>
To: <hassan@xxxxxxxx>
Cc: <si-list@xxxxxxxxxxxxx>
Sent: Friday, July 16, 2004 10:09 AM
Subject: [SI-LIST] Re: Via modeling & de-embedding
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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