[SI-LIST] Re: IBIS model for external connections
- From: "Tom Dagostino" <tom@xxxxxxxxxxxxx>
- To: "'Painter, Chris'" <chris.painter@xxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Mon, 06 Oct 2008 14:07:28 -0700
Traditional IBIS models, those of version 3.2 or lower, cannot do the
multi-level logic signaling of the 10/100/1000Base-T signaling. IBIS 3.2 and
lower assumes 1/0 logic levels. It is possible to use the extensions in
IBIS 4.2 to get where you want to go.
Tom Dagostino
Teraspeed(R) Labs
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
503-430-1285 FAX
tom@xxxxxxxxxxxxx
www.teraspeed.com
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
401-284-1827
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Painter, Chris
Sent: Monday, October 06, 2008 1:47 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: IBIS model for external connections
Brian,
I've continually run into this problem myself over the years, and have
come to the conclusion that there are no models available for Ethernet
PHYs. This is especially the case for 10/100/1000Baset-T.
I've also found myself frustrated by the maze-like naming convention for
all of this. Wikipedia has been a helpful source in digging into this.
http://en.wikipedia.org/wiki/10BASE-T
http://en.wikipedia.org/wiki/Ethernet_physical_layer
There are two important features of Ethernet signaling that I would like
to point out. The first is that the 10/100/1000 Base-T signals are
transmitted over 4 pairs. This means that the 10/100/1000 Mb/s baud
rates are not serial. The second is that NRZ modulation is not always
used. The 1000Base-T uses PAM-5 (Pulse-Amplitude Modulation):
http://en.wikipedia.org/wiki/Pulse-amplitude_modulation. The result is
that the actual frequency on any single differential pair is 125M.
I wish this could be more helpful to you for your simulation effort.
I've had to take the approach of not performing simulations for Ethernet
signals, but rather trusting good backplane layout practices to ensure
signal integrity. I've never had a design where signal integrity
problems were found on these signal types.
I've never found a definitive answer to the question of why models are
not available. I can only speculate that due to the complexity of the
modulation no one, including the device vendors, have deemed it worth
the investment in time and effort to create and validate models.
Hopefully, someone else subscribed to this list can shed more light on
this issue.
Christopher Painter (chris.painter@xxxxxxxxxxx)
Senior Electrical Design Engineer
TTM Technologies
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Sexton, Brian M. (US SSA)
Sent: Monday, October 06, 2008 2:19 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] IBIS model for external connections
All,
I need to simulate a backplane with 10/100/1000Base-T signals traveling
on it. Does anyone know how or where to get IBIS models which model the
output signals (not just signals that go chip-to-chip internal to the
system)? The Ethernet PHY models that I have do not model the signals
that exit the system (TXD_P/N and RXD_P/N). In my case, these are the
only signals I'm interested in.
Also, is there a way to use the virtex-4 ibis model to model Ethernet
the TXD_P/N and RXD_P/N signals?
Thanks,
Brian
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