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Re: [802.3_E4AI] COM starting values for 400 G

I was going round and round on quantization (I am using ENOB as point term for discussion.)  We saw a proposal for 6 bits for PAM 4 in Hossein’s presentation. 
If we take technology as a constant rather than need, then I would think there are less levels in PAM8 than PAM 4.  So the effective bits might be less. I know there is a frequency component which could suggest keeping ENOB the same all PAM for COM.

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From: Ali Ghiasi <aghiasi@xxxxxxxxx>
Sent: Thursday, June 26, 2025 6:31:17 PM
To: Richard Mellitz <richard.mellitz@xxxxxxxxx>
Cc: STDS-802-3-E4AI@xxxxxxxxxxxxxxxxx <STDS-802-3-E4AI@xxxxxxxxxxxxxxxxx>
Subject: Re: [802.3_E4AI] COM starting values for 400 G
 
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:
PAM4 = 5.0 bits
PAM6 = 5.5 bits
PAM8 = 6.0 bits.
Please also see https://ieeexplore.ieee.org/document/8310332/figures#figures

Proposed RX FFE fixed taps:
PAM4 = 30 UI
PAM6 = 25 UI
PAM8 = 20 UI

In DJ we doubled the number of taps, here is my suggestion for last floating taps:
PAM4 = 160 UI
PAM6=130 UI
PAM8 = 100 UI


Thanks,

Ali Ghiasi
Ghiasi Quantum LLC




On Jun 26, 2025, at 2:48 PM, Richard Mellitz <richard.mellitz@xxxxxxxxx> wrote:

Hi All,
 
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. 
 
 
 
pam
enob
SNR_Tx
Deterministic Jitter
A_dd
R_LM
Random Jitter
Sigma_r
Rx FFE pre taps
Px FFE post taps
Rx ffe floating tap groups
Taps per Group
Last floating tap relative to the cursor
4
6.5
33.5
0.02
0.95
0.01
8
15
2
6
100
6
6
31.5
0.022
0.93
0.011
7
12
2
5
65
8
5.5
29.5
0.023
0.9
0.012
6
10
2
4
50
 
Rich Mellitz, Samtec
 

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