[SI-LIST] Re: Relation between slew rate and ISI
- From: "Preethi Ramaswamy" <preethi.gowtham@xxxxxxxxx>
- To: "Curt McNamara" <CurtM@xxxxxxxxxxx>
- Date: Wed, 7 May 2008 16:12:22 -0700
Hi Curt
For my application, I'm trying to tap the signal to feed to a probe.
The best point to place a probe is at the receiver but it isn't always
possible.
Hence, I'm trying out a few options, one of them being tapping the signal
before the receiver.
Preethi
On 5/7/08, Curt McNamara <CurtM@xxxxxxxxxxx> wrote:
>
> 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.
> 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).
>
> 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. // principal electrical engineer
> Logic Product Development
> 411 Washington Ave. N. Suite 400
> Minneapolis, MN 55401
> T // 612.436.5178
> F // 612.672.9489
> www.logicpd.com
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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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