Hi Rich
On slide 4, there is a proposal to change the A_v, A_fe and A_ne parameters.
These are endpoint parameters, not channel parameters, and the reference termination impedance is already 46.25 Oh, so it is not clear to me why this change is required. (maybe it is – but I’d appreciate more explanation in the presentation, for the record)
Also, there should be some rationale for the proposed numbers.
A related point is whether we assume the termination of the scope (which affects measured time-domain signals) is going to be 50 Ohm or a lower value. This would affect the v_f limits. I think the current specs assume a 50 Ohm termination (which is unfortunate, but I don’t know if it is feasible to assume anything else).
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From: Bill Kirkland <00001cd3c07be0a7-dmarc-request@xxxxxxxxxxxxxxxxx>
Sent: Friday, June 13, 2025 4:59 PM
To: STDS-802-3-B400G@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_B400G] Proposal for Impedance change for IEEE P802.3dj d2.0
Rich may I suggest a small change to the order of operations in COM for s-parameters.
I would suggest changing the order of s-parameter manipulations (if they are still the same as a couple of years ago).
I believe you currently read in the channel s4p file and immediately convert to Sdd and then add in package and die s-parameters.
This works if both Rdies are 50 ohms. However if they are not, then to get COM to agree with ADS (which is really realy nice to have)
then you should:
Read in S4p’s, Convert all addition S-parameters to S4p’s, Cascade S-parameters, then re-normalize the s-parameters from 50 ohms to Rdie (both ends have to be the same), then finally convert to Sdd before computing the frequency domain transfer function.
The error in COM is not particularly large but is noticeable under certain conditions when trying to compare COM SBR with those from ADS when not using Rd = 50.
Below slide is taken from a presentation I was working on in 2020.
From: Richard Mellitz <000014533bad0b9c-dmarc-request@xxxxxxxxxxxxxxxxx>
Sent: Thursday, June 12, 2025 4:49 PM
To: STDS-802-3-B400G@xxxxxxxxxxxxxxxxx
Subject: [802.3_B400G] Proposal for Impedance change for IEEE P802.3dj d2.0
Caution: This email originated outside of Semtech. |
Hi All,
Here is a proposal for changing the reference impedance for d2.0 to 92.5 ohms differential and 23.125 ohms common mode since the target impedance for test fixture was change.
The is no change to the COM computation algorithm required. There are several sections that are touched by this.
Comments? Thoughts?
Regards,
Richard Mellitz
Samtec
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