[SI-LIST] Re: Undershoot issues
- From: <vani.chandrasekharan@xxxxxxxxx>
- To: <art_porter@xxxxxxxxxxx>, <jory_mckinley@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Thu, 23 Aug 2007 09:07:04 +0530
I have observed this issue in some interfaces at 133MHz rate too, I
observe undershoots of 40% compared to the allowed percentage of 27%.
Would you consider this going a little overboard?
Either way thanks a lot for all your valuable insights in this issue.
Will try and analyze!
Thanks and warm regards,
Vani
________________________________
From: art_porter@xxxxxxxxxxx [mailto:art_porter@xxxxxxxxxxx]
Sent: Wednesday, August 22, 2007 10:24 PM
To: jory_mckinley@xxxxxxxxx; Vani Chandrasekharan (WT01 - Embedded &
Product Engineering); art_porter@xxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: RE: [SI-LIST] Re: Undershoot issues
Yeah, I missed the part about 50 MHz. ISI should never be a problem at
that slow data rate (unless the undershoot is really extreme).
Art
________________________________
From: Jory McKinley [mailto:jory_mckinley@xxxxxxxxx]
Sent: Wednesday, August 22, 2007 10:47 AM
To: vani.chandrasekharan@xxxxxxxxx; art_porter@xxxxxxxxxxx;
si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Re: Undershoot issues
I have not seen ISI cause over/undershoot at this slow toggle rate but
another area you may want to check is potential crosstalk pull-in (same
edges toggling together given a slightly larger forward capacitive
coupling coefficient between traces).
-Jory
----- Original Message ----
From: "vani.chandrasekharan@xxxxxxxxx" <vani.chandrasekharan@xxxxxxxxx>
To: art_porter@xxxxxxxxxxx; jory_mckinley@xxxxxxxxx;
si-list@xxxxxxxxxxxxx
Sent: Wednesday, August 22, 2007 9:10:18 AM
Subject: [SI-LIST] Re: Undershoot issues
=20
Hi Art Porter,
I am curious how ISI is related to undershoot, could you please
enlighten me on that?
Thanks and warm regards,
Vani
-----Original Message-----
From: art_porter@xxxxxxxxxxx [mailto:art_porter@xxxxxxxxxxx]=20
Sent: Wednesday, August 22, 2007 7:18 PM
To: jory_mckinley@xxxxxxxxx; Vani Chandrasekharan (WT01 - Embedded &
Product Engineering); si-list@xxxxxxxxxxxxx
Subject: RE: [SI-LIST] Re: Undershoot issues
Undershoot could be an indicator of ISI, which could increase the jitter
and lead to poor bit error rates, so you shouldn't ignore it.
Art Porter=20
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Jory McKinley
Sent: Tuesday, August 21, 2007 11:08 PM
To: vani.chandrasekharan@xxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Undershoot issues
Undershoot may not be a problem in your case(s) depending on the
amplitude and duration. Do you have the input specs for the devices
affected? Most technologies have a 300mV rating or so DC level above
and below the supply and some have an AC level spec which allows for
more of an overshoot/undershoot but only for some period of time. If you
have a real problem look to better match the trace terminations with
your trace impedance and/or if budget allows slow down the drivers
somewhat. You should be able to do this in simulation since it appears
you have reasonable lab correlation.
-Jory
----- Original Message ----
From: "vani.chandrasekharan@xxxxxxxxx" <vani.chandrasekharan@xxxxxxxxx>
To: si-list@xxxxxxxxxxxxx
Sent: Tuesday, August 21, 2007 11:10:22 PM
Subject: [SI-LIST] Undershoot issues
=3D20
Hi,
I am observing undershoot alone in my simulation and also in some of the
on-borad captures of some signals(single ended, less than 50MHz). I am
not sure how to mitigate this issue and how to rootcause this problem.
Kindly give me some perspective on this issue and also some options I
can try to mitigate the same.
Thanks and warm regards,
Vani
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