[SI-LIST] Re: Can I get this from an IBIS model?

Doug

I agree with Scott's approach, but remember that the Pullup curves are
referenced to VDDQ not VSS. The actual voltage for pullups are defined by
either
[Voltage Range] or  [Pullup Reference]. For Pulldowns, the reference is
either VSS or
[Pulldown Reference]. I use the Vswing/2 as my measurement point.

 For Pulldowns  Pulldown_Imped = (Vtable - Pulldown_Reference)/Itable

 For Pullups    Pullup_Imped  = -(Pullup_Reference - Vtable)/Itable


Doug

Douglas Burns
Principal Consultant
Signal Integrity Software, Inc
6 Clock Tower Place
Maynard, MA 01754
978-461-0449
dburns@xxxxxxxxxx

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Scott McMorrow
Sent: Saturday, September 28, 2002 1:12 AM
To: doug@xxxxxxxxxx; silist
Subject: [SI-LIST] Re: Can I get this from an IBIS model?



Doug,

go to the I/V curves and at  1 Volt compute the output resistance.  The
behavior here is fairly indicative of the impedance across most of the
output range.

Z = E/I

At 1 volt in the table, the impedance is the inverse of the current.
 From this you can build a table of the range of impedance of the device
from min to max, rising and falling edge.

best regards,

scott

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



Doug Brooks wrote:

>Suppose I have an IBIS model, but not the physical part. Is there a way I
>can determine the output impedance of the device (and if different, the
>output impedance for each digital state) from the IBIS model itself?
>
>I know I can build a simulation and solve for the output impedance that
>way, but can I get it from the IBIS model itself without going through the
>simulation step? . And if so, where in a model do I look?
>
>Thanks for any help.
>
>Doug Brooks
>
>___________________________________________________________________________
____
>UltraCAD Design announces availability of its new book "Signal Integrity
>Issues in PCB Design"
>Details at  www.ultracad.com
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