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Re: [802.3_B400G_ELEC] PKG model mode conversion - Follow up on yesterday's question

Hello Rich/Liav,

I respectively 0.8 dB and 1.0 dB mode conversion for package A and B BGA transition to PCB, Mike Li presentation show mode conversion for 1 mm and 0.5 mm package.
https://www.ieee802.org/3/df/public/22_03/mli_3df_01a_220316.pdf

Lets wait an see to hear back on Liav how small is mode conversion for package B, and if we need to add some penalty for it in COM.  At this point in Ghiasi_3dj_02a these are place holder that I expected will be reduced with more data and that will help address C2M application with lower bump-bump loss than suggested in contribution.

Based on what Liav says below package B mode conversion was reduced to something smaller than 1 dB I assumed in my bottom up analysis
https://www.ieee802.org/3/dj/public/23_09/ghiasi_3dj_02a_2309.pdf

In response to Rich comment on the DM to CM or CM to DM conversion these are captured by the s-parameters and would be reflected in the loss, in addition we also have limit on CM generation at various test point to prevent excessive CM voltage on a receiver that may need to operated with few mV of signal..

Thanks,

Ali Ghiasi
Ghiasi Quantum LLC




On Sep 13, 2023, at 10:19 AM, Richard Mellitz <000014533bad0b9c-dmarc-request@xxxxxxxxxxxxxxxxx> wrote:

I think mode conversion is a complicated mater. Many effects are covered or included in the transmitter and receiver specification. For example, p-n skew and imbalance directly affect p_max/V_f.  There are other effects which may not be included such at DM to CM and back to CM to DM conversion in the package model. We do have SCMR limit. Presently we do not use a SCMR derived parameter in COM.  Instead, perhaps a bit of over budgeting is not a bad thing as Liav indicated.  The COM package model strategy and COM strategy are similar. That is it is performance you must meet and not the performance you get. (Paraphrased from conversation with John Calvin). I think the package model is much like the 3dB COM limit and should be a like a global budget for specific design choices.
… Rich
 

Richard Mellitz
Samtec Southeast
Office: 803-908-4411
From: Liav Ben Artsi <liav@xxxxxxxxxxx> 
Sent: Wednesday, September 13, 2023 8:55 AM
To: STDS-802-3-B400G-ELEC@xxxxxxxxxxxxxxxxx
Subject: [802.3_B400G_ELEC] PKG model mode conversion - Follow up on yesterday's question
 
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Hi All,
Yesterday Ali referred a question to me regarding the package model mode conversion value.
I wanted to provide a better answer than “negligible”.
After going back to check on the exact value, I found the mode conversion of the models supplied to be better than -30dB all the way up to above 60GHz (actually in some of the models I was seeing also better than -36) – Further tuning of de-skew, etc. may take the value even lower.
All that said, one needs to keep in mind that these models are synthetic, and lack much of the routing complexity of actual package routing.
Such complexity may force higher conversion results, which we actually may want to take into account in the budgeting of the spec (and I guess that was what Ali was referring to).
Exact impact of mode conversion in dB loss (of actual case packages), yet to be exactly analyzed, but…
Once we analyze it, IMHO, we will need to use this “a bit over valuated budget” to account for other parts of the same table which were undervalued.  
Best regards,
--Liav
 
 

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