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

A little history

Clause 93 KR4 NRZ – SNR_TX=27

Clause 94 KP4 PAM4 – SNR_TX-31

What you suggest is in line with what we did before.

 

Should we start with PAM4 at 31.5  dB or 33.5 dB considering we are now using signal power rather than peak.

May be:

PAM4 = 33.5

PAM6= 34

PAM8 = 34.5

 

… Rich

 

From: Mike Dudek <mdudek@xxxxxxxxxxx>
Sent: Thursday, June 26, 2025 6:57 PM
To: STDS-802-3-E4AI@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_E4AI] [EXTERNAL] Re: [802.3_E4AI] COM starting values for 400 G

 

The SNRtx is also going in the wrong direction.   The bandwidth of measurement is less for PAM8  (and it is also more susceptible so it needs better SNRtx.   Would suggest

 

PAM4 = 31.5

PAM6= 32.5

PAM8 = 33.5

 

 

The random jitter and deterministic jitter are already in UI.  I think as a starting point one could make them the same in UI,  but probably better to say they are the same in ps

 

RLM I think should also not be going in the direction you suggest.   Having the same 0.95 value for PAM4 makes sense, but 0.97 for PAM6 and 0.98 for PAM8 is going to be more what is needed.

From: Ali Ghiasi <aghiasi@xxxxxxxxx>
Sent: Thursday, June 26, 2025 3:31 PM
To: STDS-802-3-E4AI@xxxxxxxxxxxxxxxxx
Subject: [EXTERNAL] 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

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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.

 

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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