Subject: Stacked TSOP modeling

From: rrwolff <[email-masked]>
Date: Tue, 17 Jul 2001 09:51:39 -0600

I am looking for suggestions on how to model a stacked TSOP (or a TwoSOP)
arrangement in IBIS.  Functionally, only one component in the stacked
arrangement is active at any given time.  However, the power and ground
clamp diodes as well as the die capacitance of the second component will
influence the first componenent's operation.  

I've thought of two ways to model this so far.  The first is with a complex
package model with a fork statement describing the trace to the second
component and a capacitor for the C_comp of the stacked component.  In this
method, the [Model] of the original component would not change.  The
downside of this method is that the power and ground clamp curves of the
second component are not modeled.

The second method is to model the entire arrangement in SPICE.  The loading
effect of the stacked component and package would then be included in the
I-V and V-T curves of the model.  However, with the model used in input mode
in a simulator, the effect of the complex package and extra die capacitance
would not be modeled correctly.

There must be a better way to do this, and I'm sure someone has modeled this
situation before with IBIS.  So, any help you can give me is greatly
appreciated.

Thanks,
Randy Wolff

---

From: Scott McMorrow <[email-masked]>
Date: Tue, 17 Jul 2001 09:29:12 -0700

Randy,

Stacked TSOP packages will have some extremely interesting models
in reality because of the height above the board for the second device
and it's coupling to the neighbor.  It's an interesting 3D problem.

IBIS does not handle coupled package models well.  However, what
you can do is to take the model produced by a 3D modeler and
for each trace, develop the single ended even and odd mode
trace parameters.  These can even be done in multiple sections to
better model the actual physical situation.  Then, this can be converted
into an IBIS EBD model.  An EBD model will allow you to model
multiple model sections and multiple I/O's.

regards,

scott

--
Scott McMorrow
Principal Engineer
SiQual, Signal Quality Engineering
18735 SW Boones Ferry Road
Tualatin, OR  97062-3090
(503) 885-1231
http://www.siqual.com