FreeLists / si-list / [SI-LIST] Re: Modeling a MUX/DEMUX?

["Scott McMorrow" <scott@xxxxxxxxxxxxx>]

Brian,

A FET switch is a highly non-linear device.  Single line modeling will 
be only very appoximate.  I would highly advise you to perform your 
simulation with a Spice model of the device and package to see what the 
device will really do. IDT seems to have these on their website.

One area that we discovered a while back was the large amount of 
crosstalk from switch to switch that is coupled through the substrate, 
due to the large inductance of the packaging.  Due to inductive 
isolation of the die from the board ground, there is a coupling path 
from the FET switches through the substrate.  We saw extremely high 
crosstalk due to these effects in PCI and PCIX hot-swap applications 
when multiple signals were switching simultaneously.

Looking at this part,

IDTQS3VH257 

there are up to 4 active switching lines in a leadframe package with 
only one ground, and that ground is at the corner of the package (the 
absolute worst place for inductance).  I'd be concerned about what might 
happen worst case.

best regards,a


scott

-- 
Scott McMorrow
Teraspeed Consulting Group LLC
2926 SE Yamhill St.
Portland, OR 97214
(503) 239-5536
http://www.teraspeed.com



Aspnes, Brian D wrote:

>If you wanted to model the IDT MUX parts IDTQS3VH257 and IDTQS3VH253 =
>for
>pre-layout simulations, in a series net configuration [such that the
>MUX/DEMUX is in series with your trace ("Y" to "In", with select and =
>enable
>"on")], how would you model the MUXs with a Single Line Lumped Model =
>"SLM"
>type environment (we use Innoveda Scratchpad/ePlanner which uses .ibs =
>models
>and "schematic" versions of connectors/bus switches). =A0
>
>Driver -> Trace -> MUX/DEMUX -> Trace -> Receiver=20
>=A0
>Does anyone have a Single Line Lumped Model (SLM with one input, one =
>output)
>that I can use for signal integrity analysis similar to this connector =
>model
>from AMP (Mictor): =
>http://www.amp.com/simulation/scripts/models.asp#list=20
>=A0
>Brian Aspnes
>Intel Communications Group (ICG)
>E-mail: brian.d.aspnes@xxxxxxxxx
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