[SI-LIST] Re: Via Impedance!
- From: Gregory R Edlund <gedlund@xxxxxxxxxx>
- To: srini@xxxxxxxxxxxx
- Date: Thu, 15 Jul 2004 15:17:49 -0500
Dear G. Srinivasan,
The last time I checked, SpecctraQuest was using a closed-form equation to
calculate via capacitance. Perhaps there is a new version available. Off
the top of my head, I would estimate that if you're below 0.062 in. card
thickness and 1 GHz bandwidth, this simple lumped model is sufficient. My
colleagues and I did a paper for DesignCon 2004 about full-wave
electromagnetic modeling of vias at frequencies between 1 and 10 GHz. Let
me know if you'd like a copy. Somewhere between the lumped capacitance
model and the full-wave model there is probably a place for quasi-static
modeling, e.g. if you're looking for a more accurate prediction of
capacitance. However, if magnetic effects are significant I don't think
you're going to get the right answer using a quasi-static solver because
the path the current takes is very much a transient phenomenon.
I read a good paper on via modeling a while back:
"Designing Controlled-Impedance Vias," Thomas Neu, EDN, October 2, 2003
If you're looking for a simple formula to calculate via lumped
capacitance, try this:
"High-Speed Digital Design," Howard Johnson & Martin Graham, page 257
Greg Edlund
Senior Engineer
Signal Integrity
IBM Engineering and Technology Services
3605 Hwy. 52 N, Dept. HDC
Rochester, MN 55901
gedlund@xxxxxxxxxx
Msg: #4 in digest
Date: Wed, 14 Jul 2004 12:17:52 -0000
Subject: [SI-LIST] Via Impedance!
From: "G.Srinivasan" <srini@xxxxxxxxxxxx>
Hi,
I have a querry regarding how to ensure that the impedance of the via is
the same as that of the traces. For example, if I have a trace of 50 ohms
running between two layers through a via, how can I calculate its
impedance?
In Specctraquest, I saw that there is a field solver that generates a
model
for the via based on its geometry and uses it for simulation. Does it also
gives the impedance of the via and provides help to achieve the required
via
impedance?
Regards,
G.Srinivasan.
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