Subject: IBIS Package Model

From: [email-masked]
Date: Wed, 17 Mar 1999 17:35:40 -0600

Mike,

Can you elaborate a little more?  It sounds like you're trying to model the
ground plane in a package as a non-ideal return path.  Usually we make the
assumption in transmission line analysis that the return terminals are
connected to ideal ground, but this doesn't work when you're modeling power
rail collapse on an IC due to package inductance.  It sounds like you want
a package model with two ports for each signal conductor and more than two
ports for the ground conductor.  Is this the case?  If so, you're talking
about a 3-D package model since a package model based on a 2-D cross
section would only have two ports for a non-ideal ground.

The quick answer is that IBIS can do coupled lumped package models or
uncoupled distributed package models, but not coupled distributed package
models.  In my experience, I've used multiple lumped segments to describe a
package; these were based on multiple unique 2-D cross sections with
non-ideal grounds.  However, I've never seen anyone derive a coupled
distributed package model from a 3-D field analysis.

Greg Edlund
Advisory Engineer, Critical Net Analysis
IBM
3650 Hwy. 52 N, Dept. HDC
Rochester, MN 55901
[email-masked]

---------------------- Forwarded by Gregory R Edlund/Rochester/IBM on
03/17/99 05:21 PM ---------------------------

"Mike Lamson" <[email-masked]> on 03/17/99 07:46:27 AM

Please respond to [email-masked]

To:   [email-masked]
cc:    (bcc: Gregory R Edlund/Rochester/IBM)
Subject:  IBIS Package Model

Does anyone know how to represent RLC in IBIS for a ground plane with
multiport nodes?  The issues is the capacitance.  The inductance and
resistance can be described between any two ports of the plane but how to
represent the capacitance in IBIS is a mystery.  If the total plane
capacitance is used, it gets repeated for each port which over estimates it
in the model.

Thanks,

Mike Lamson
[email-masked]

---

From: Fred Balistreri <[email-masked]>
Date: Wed, 17 Mar 1999 17:16:01 -0800

> capacitance is used, it gets repeated for each port which over estimates it
Full wave solvers will give you S parameters. These can be interpreted 
into SPICE Laplace transfer functions that retain the frequency effects.
Therefore its possible to have the behavior of the system modeled in
a simulator accurately. Other approaches involve FDTD and similiar
methods. However Mike's question pertains to IBIS. In that regard
Greg's answer seems correct. Lumped RLC circuits from 3d analysis can
become large and hard to handle by time domain simulation.  

Best Regards,
-- 
Fred Balistreri
[email-masked]

http://www.apsimtech.com