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Re: [802.3_B400G_ELEC] Topic: Floating taps for Rx FFE

Your observations suggest that there is an issue with the implementation of the "FOM method" and, in my opinion, efforts should be focused on correcting the implementation rather than adding options for alternatives.
I say this because, by definition, a search that optimizes FOM should always result in the best FOM and I do not immediately see anything inherent to a FOM-based search that would result in "blocking" issues.


On Thu, Mar 21, 2024 at 10:22 AM Richard Mellitz <000014533bad0b9c-dmarc-request@xxxxxxxxxxxxxxxxx> wrote:

Hi All,

 

In COM 4.4 there are 2 selections to compute the floating taps controlled by the following spreadsheet table entry

 

RXFFE FLOAT CTL

ISI

 

FOM o ISI

 

If there are 1 or 2 groups of tap the FOM method may be as good or better than the ISI method invoked respectively by functions “ findbankloc” and “ FOM_rxffe_floating_taps”.

 

However, 3 or more groups may exhibit a search blocking issue for FOM which ISI method does not have.

 

In many cases I have seen the ISI method yield a slightly better ( a few hundredths of dB)  FOM than the FOM method.

I was thinking of checking both methods unless someone has a better idea for the FOM method that accounts for blocking better.

 

Thoughts,

 

… Rich

 

Richard Mellitz

Samtec Southeast

Office: 803-908-4411

www.samtec.com


 

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