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Re: [802.3_B400G] FYI: Proposal to specify a control for skew in IEEE P802.3dj 2.0

Subject: Re: [802.3_B400G] FYI: Proposal to specify a control for skew in IEEE P802.3dj 2.0

From: Hansel DSilva <00004708d0869f3e-dmarc-request@xxxxxxxxxxxxxxxxx>

Date: Mon, 23 Jun 2025 15:32:02 +0000

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Reply-to: Hansel DSilva <Hansel.D'Silva@xxxxxxxxxxxxxxxx>

Thread-index: Advb26FuYLO9jo24R9K7x/i/Vavp5gIc9gan

Thread-topic: [802.3_B400G] FYI: Proposal to specify a control for skew in IEEE P802.3dj 2.0

Hi Richard,

In the attached proposal regarding using SCMR_CH (for the channel) to control skew and other imbalances, I noticed that only SCD21 is mentioned. Would the proposal include computing SCMR_CH using SDC21 as well?

Below is my reasoning behind this question.

SCMR for the transmitter electrical characteristics.

- Equation 178-1 in D2P0.

- D2p0 mentions VCM_FB as the full-band peak-to-peak AC common-mode voltage defined by the method specified in 179.9.4.1 and measured with the transmitter equalization set to “no Equalization”.

- I interpret this as calling out the differential-mode to common-mode insertion loss (SCD21).
TP0 to TP5- Channel mode conversion insertion loss.

- Equation 178-6 and 178-7 in D2p0.

- It calls out differential-mode to common insertion loss (SCD21) and common-mode to differential-mode insertion loss (SDC21).
Differential insertion loss is reciprocal, but mode-conversion is not reciprocal in the conventional sense.

- Assuming the throughs are (1)---(2) and (3)---(4).

-Differential insertion loss is reciprocal, meaning SDD21 ≈ SDD12.

SDD21= 0.5*(S21 - S23+ S43- S41).

SDD12= 0.5*(S12 - S32+ S34- S14).

- Mode conversion terms are not strictly reciprocal:

SCD21 ≈ SDC12 and SCD12 ≈ SDC21.

- However, SCD21 ≠ SCD12, as shown in the following equations:

SCD21= 0.5*(S21 - S23 + S41 - S43).

SCD12 = 0.5*(S21 + S32 - S14 - S34).

SDC21 = 0.5*(S12 + S23 -S41 -S43).

SDC12 = 0.5*(S12 - S32 + S14 - S34).

Regards,

Hansel D'Silva

From: Richard Mellitz <richard.mellitz@xxxxxxxxx>
Sent: Friday, June 13, 2025 4:54 AM
To: STDS-802-3-B400G@xxxxxxxxxxxxxxxxx <STDS-802-3-B400G@xxxxxxxxxxxxxxxxx>
Subject: [802.3_B400G] FYI: Proposal to specify a control for skew in IEEE P802.3dj 2.0

CAUTION: EXTERNAL EMAIL

Hi All,

The has been presented some this before. This this attached is a proposal for using SCMR_CH (for the channel) to control skew and other imbalances. The first half, SCMR and V_CM was controlled in the transmitters. This proposal it to complete the process for the channels.

Comments? Thoughts?

Regards,

Richard Mellitz

Samtec

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