[SI-LIST] Re: Can I get this from an IBIS model?
- From: "Douglas Burns" <dburns@xxxxxxxxxx>
- To: <scott@xxxxxxxxxxxxx>, <doug@xxxxxxxxxx>,"silist" <si-list@xxxxxxxxxxxxx>
- Date: Mon, 30 Sep 2002 08:57:56 -0400
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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>
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