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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.

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

0.02

0.95

0.01

8

22

30

2

6

160

6

5.5

32.5

0.022

0.97

0.011

7

28

35

2

5

120

8

6

33.5

0.023

0.98

0.012

6

14

20

2

4

100

 

Would this be  reasonable start point for channel analysis?

 

From: Bowman, Kurtis <Kurtis.Bowman@xxxxxxx>
Sent: Thursday, June 26, 2025 9:03 PM
To: richard.mellitz@xxxxxxxxx; STDS-802-3-E4AI@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_E4AI] COM starting values for 400 G

 

[AMD Official Use Only - AMD Internal Distribution Only]

 

Good to know. I’m certainly not a n expert here either 

 

Thanks,

Kurtis 

From: Richard Mellitz <richard.mellitz@xxxxxxxxx>
Sent: Friday, June 27, 2025 8:49:34 AM
To: STDS-802-3-E4AI@xxxxxxxxxxxxxxxxx <STDS-802-3-E4AI@xxxxxxxxxxxxxxxxx>
Subject: Re: [802.3_E4AI] COM starting values for 400 G

 

Caution: This message originated from an External Source. Use proper caution when opening attachments, clicking links, or responding.

 

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.

 

 

From: Ali Ghiasi <aghiasi@xxxxxxxxx>
Sent: Thursday, June 26, 2025 6:31 PM
To: Richard Mellitz <richard.mellitz@xxxxxxxxx>
Cc: 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.

 

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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