Good response Todd. The following are things to look out for in correlation. - short channels with low loss and high return loss. - If you correlate with poorly terminated channels, or channels with built-in high-Q discontinuities, then the lack of correct analog modeling is readily seen. - In-package NEXT and FEXT is amplified by increased return loss. - Tx-Tx, Rx-Rx, and Tx-Rx crosstalk correlation can easily see 3 dB or more error when analog filtering is not modeled correctly. - Jitter will be affected significantly. - 8ps jitter mismatch may not seem like much, but that's 8% of a 10G channel, and 20% of a 25G channel. On Thu, Mar 8, 2012 at 1:52 PM, Todd Westerhoff <twesterh@xxxxxxxxxx> wrote: > Terry,**** > > ** ** > > If you idealize either the TX analog driver or the RX termination network, > you will miss the interaction that component has with the channel, and the > ISI that results from it. While you can model an analog output transfer > function inside the algorithmic model, but you won’t get **any** of the > reflections that result from the discontinuities (e.g. capacitance) > presented by the TX output or the ISI that results from that.**** > > ** ** > > Depending on your measurement setup, it’s easy to miss this … or, for that > matter, to misdiagnose much of the ISI as jitter. Bottom line, IBIS-AMI > assumes that the “analog channel” captures the combined behavior of the TX > analog output – channel – RX termination network, and idealizing either the > TX or RX analog models violates that assumption.**** > > ** ** > > And – I repeat – it’s easy to miss. There are lots of cases where things > look like they correlate (at least initially) when they actually don’t.*** > * > > ** ** > > My $0.02.**** > > ** ** > > Todd. **** > > ** ** > > [image: Description: > cid:EAFF2D52-4B63-4A05-9D24-B96BE375B7E0@eau.wi.charter.com] > > **** > > *Todd Westerhoff***** > > VP, Software Products**** > > ** ** > > Signal Integrity Software Inc. • www.sisoft.com**** > > 6 Clock Tower Place • Suite 250 • Maynard, MA 01754**** > > (978) 461-0449 x24 • twesterh@xxxxxxxxxx**** > > * * > > * * > > *“*Three in the morning and I'm still awake, > So I picked up a pen and a page … ”**** > > -Sidewalk Prophets**** > > ** ** > > *From:* ibis-macro-bounce@xxxxxxxxxxxxx [mailto: > ibis-macro-bounce@xxxxxxxxxxxxx] *On Behalf Of *Chen, Terry > *Sent:* Thursday, March 08, 2012 1:33 PM > *To:* DBanas@xxxxxxxxxx; 'IBIS-ATM' > *Subject:* [ibis-macro] Re: Question on dividing up the Tx behavior > between the AMI and analog portions of the model**** > > ** ** > > Hi David,**** > > ** ** > > Actually I am interested in other’s response to this question as well…**** > > ** ** > > But, for the TX Driver I am currently modeling, I am doing exactly what > you have prescribed and using the IBIS-analog portion as effectively an > ideal step function (by setting my ramp with extremely high rise/fall > dv/dt) and letting the step response filter inside my AMI model to shape my > output waveform. Now, I am not sure if this is the “right” or “ideal” way > to do it, but I am getting a reasonably good correlation in my Re-driver > model with the actual lab measurements (the max jitter mismatch is < 8ps). > **** > > ** ** > > I hope this is at least an useful data point for you.**** > > ** ** > > Regards,**** > > Terry**** > > ** ** > > *From:* ibis-macro-bounce@xxxxxxxxxxxxx > [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] *On Behalf Of *David Banas > *Sent:* Thursday, March 08, 2012 1:15 PM > *To:* 'IBIS-ATM' > *Subject:* [ibis-macro] Question on dividing up the Tx behavior between > the AMI and analog portions of the model**** > > ** ** > > Hi all,**** > > ** ** > > Is it customary to split up the Tx behavior, such that the FFE is modeled > in the AMI model and the pulse shaper in the analog model?**** > > Or, is there a different dividing line that has been identified as “best > practice”.**** > > (Or, am I completely off in the weeds?)**** > > ** ** > > The context for this question: I just managed to get good correlation > between our latest Tx AMI model and the HSPICE model.**** > > And then I realized that, having dumped all of the behavior into the AMI > model, I would need to put an ideal step function into the V-T curves of > the analog IBIS model. And I wasn’t sure that would be a good idea. (I’m > guessing that that would reek havoc in most simulators; is that correct?)* > *** > > ** ** > > Thanks,**** > > ** ** > > *David Banas* > > *Sr. Member Technical Staff* > > Altera <http://www.altera.com/>**** > > +1-408-544-7667 - desk**** > > * * > > *Did you know Altera offers over 150 free online technical training > courses<http://www.altera.com/servlets/searchcourse?coursetype=Online&WT.mc_id=t9_ot_mi_mi_tx_a_311>? > Take one today!* > > ** ** > > ** ** > ------------------------------ > > Confidentiality Notice. > This message may contain information that is confidential or otherwise > protected from disclosure. If you are not the intended recipient, you are > hereby notified that any use, disclosure, dissemination, distribution, or > copying of this message, or any attachments, is strictly prohibited. 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