I support Mike Dudek’s position on Jitter ( in Ui terms) both A_dd and Rj
keep in ps terms the same
-Upen
From:
Mike Dudek <mdudek@xxxxxxxxxxx>
Date: Monday, June 30, 2025 at 4:16 PM
To: STDS-802-3-E4AI@xxxxxxxxxxxxxxxxx <STDS-802-3-E4AI@xxxxxxxxxxxxxxxxx>
Subject: Re: [802.3_E4AI] [EXTERNAL] Re: [802.3_E4AI] COM starting values for 400 G
I still think the jitter numbers (which are in UI) should not be increasing with modulation level. (Maybe even go the other way keeping them the same in ps), but at least leave them the same (in UI as 802.3dj).
From: Richard Mellitz <richard.mellitz@xxxxxxxxx>
Sent: Monday, June 30, 2025 1:26 PM
To: STDS-802-3-E4AI@xxxxxxxxxxxxxxxxx
Subject: [EXTERNAL] Re: [802.3_E4AI] COM starting values for 400 G
I have this for inputs so far. pam enob SNR_Tx Deterministic Jitter R_LM Random Jitter Rx FFE pre taps Px FFE post taps Rx FFE total taps Rx ffe floating tap groups Taps per Group Last floating
tap relative to the cursor A_dd Sigma_r 4 5 31. 5
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I have this for inputs so far.
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pam
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enob
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SNR_Tx
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Deterministic Jitter
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R_LM
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Random Jitter
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Rx FFE pre taps
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Px FFE post taps
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Rx FFE total taps
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Rx ffe floating tap groups
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Taps per Group
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Last floating tap relative to the cursor
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A_dd
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Sigma_r
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4
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5
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31.5
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0.02
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0.95
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0.01
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8
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22
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30
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2
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6
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160
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6
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5.5
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32.5
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0.022
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0.97
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0.011
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7
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28
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35
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2
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5
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120
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8
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6
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33.5
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0.023
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0.98
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0.012
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6
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14
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20
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2
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4
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100
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Would this be reasonable start point for channel analysis?
[AMD Official Use Only - AMD Internal Distribution Only]
Good to know. I’m certainly not a n expert here either
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For KR4 (NRZ) we used Nb= 14
For KP4 (PAM4) we used Nb= 16
I can’t remember why though.
Which is the opposite direction of what you were suggesting below.
Hello Rich,
ADC ENOB is defend as = (SNDR - 1.76 dB)/6.02, furthermore SNDR and ENOB are frequency dependent. PAM4 with higher frequency will have lower ENOB, my suggestion is the following for ENOB:
Proposed RX FFE fixed taps:
In DJ we doubled the number of taps, here is my suggestion for last floating taps:
Thanks,
Ali Ghiasi
Ghiasi Quantum LLC
I put together a stake in the ground for 400 Gb/s COM so we can better analyze channels.
This not a recommendation. It’s starting point for consensus discussion. I’m not convinced the progression direction is correct for some the parameter makes sense. I can argue either way.
Comments and suggestions welcome.
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Deterministic Jitter
A_dd
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Rx ffe floating tap groups
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Last floating tap relative to the cursor
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