[ibis-quality] IV curve sweep range
- From: "Mirmak, Michael" <michael.mirmak@xxxxxxxxx>
- To: <ibis-quality@xxxxxxxxxxxxx>
- Date: Tue, 12 Jul 2005 12:00:15 -0700
Forwarded from Arpad Muranyi...
- MM
-----Original Message-----
From: Muranyi, Arpad
Sent: Tuesday, July 12, 2005 11:20 AM
To: ibis-quality-bounce@xxxxxxxxxxxxx
Cc: Mirmak, Michael
Subject: IV curve sweep range
Hello everyone,
I am not monitoring this email reflector, and I don't plan on
subscribing, but Mike Mirmak forwarded me a message regarding the IV
curve sweep range discussion, to which I would like to add a few
comments. I don't know what exactly is being proposed, I am just going
to mention my views here.
The problem I see is that IBIS requires a sweep range of -Vcc to 2*Vcc.
This comes from the days when most buffers switched rail to rail and
most buses were unterminated. The reason for this range stems from the
T-line reflection theory, that the signal can double at the end of the
line. If we had a strong driver, which could drive close to the rail,
then the doubling of this signal could span a range close to -Vcc or
+2*Vcc assuming no clamping effects at the end of the line.
The problem is that most modern buses and drivers are not operating like
this any more. For one, the signal swing
doesn't go rail-to-rail any more, and second, most buses are terminated.
Even if we ignore the termination question, the reduced-swing signaling
alone warrants a reconsideration of the IBIS rule.
One of my favorite examples is GTL. The signal goes from a low level
between 0-0.5V to a high level of 1.5V. If I took 0-1.5, even if I
doubled the signal swing on the top and bottom, I would get a range of
-1.5V to 3.0V. Aside from the fact that the bus is terminated and we
will never see a doubling at the end of the T-line, compare this range
with what IBIS would require if this buffer was powered by 3.3V: it
would be -3.6V to 6.6V, almost double! This clearly doesn't make sense.
I would propose that we should write a BIRD on this, and change the IBIS
specification so that it would not REQUIRE the range of -Vcc to 2*Vcc.
I am not sure what it should say yet, but I would definitely NOT favor
that the parser should be changed to check the ranges in the IBIS files
against the IBIS rules. I would much prefer to have a rule that is
based on signaling, though I have to admit that this may be somewhat
more complicated to spell out.
Please comment,
Arpad
===========================================================
---------------------------------------------------------------------
IBIS Quality website: http://www.eda.org/pub/ibis/quality_wip/
IBIS Quality archives: //www.freelists.org/archives/ibis-quality
To unsubscribe send an email:
To: ibis-quality-request@xxxxxxxxxxxxx
Subject: unsubscribe
Other related posts:
