[SI-LIST] Re: Relation between slew rate and ISI
- From: "Curt McNamara" <CurtM@xxxxxxxxxxx>
- To: "Preethi Ramaswamy" <preethi.gowtham@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Wed, 7 May 2008 16:43:11 -0500
This may have been covered already by Wolfgang's excellent responses:
The wave arrives at the load and any reflected energy is almost no prop =
delay away.=20
In contrast, at other points on the line the reflected energy from the =
load (or other discontinuity) arrives 2 x tpd later (where tpd is the =
delay from the measurement point to the reflection).=20
This is one reason we may not care about intermediate points on the =
line: at the load we need to see signal quality and establish that there =
are no voltage levels beyond our limits. At the source signal quality =
may not be as critical, but checking voltage levels is important.
Why would we care about intermediate points? They could affect crosstalk =
or emissions. Any other perspectives on this?
Curt
Curt McNamara, P.E.=A0// principal electrical engineer=20
Logic Product Development
411 Washington Ave. N. Suite 400
Minneapolis, MN 55401
T // 612.436.5178
F // 612.672.9489
www.logicpd.com=20
/ / / / / / / / / / / / / / / / / / / / / / / / /=20
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-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
On Behalf Of Preethi Ramaswamy
Sent: Tuesday, May 06, 2008 5:52 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Relation between slew rate and ISI
I'm looking for some information on the relation between slew rate and =
ISI
effect on high speed memory data signals.
From my SI simulation I'm observing that a signal looks much worse with =
a
higher slew rate than a lower slew rate. But the point I'm tapping is =
not at
the receiver but a point before the receiver. I don't expect the signal =
to
look as good as at the receiver but I was hoping that the trends match. =
At
the receiver itself, the fast corner signal looks better than the slow
corner signal. The bus is properly terminated.
Looking at the waveform, I see that in the fast corner case, whenever =
there
is a 1010 pattern, the signal is not reaching its intended Vhigh and =
Vlow
level. A similar thing happens at the slow corner but the signal swing =
is
much better. Hence, the eye diagram in the fast corner is almost closed
whereas the slow corner looks open.
While searching some artciles on this, I found the opposite stated. It =
said
that ISI effects are more pronounced in the slow corner case and =
Crosstalk
is more pronounced in the fast corner case.
Any experience or insight into this topic would be very helpful.
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