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Re: [STDS-802-3-400G] IEEE P802.3bs TDECQ optimizing eye time centre of eye

Hi Jonathan,


You brought up the great point, this is exactly the issue I was talking about especially for such directly modulated transmitters like VCSEL and DML because of relevant laser characteristics. I’ve told Mark and John that I’m assembling some slides to show critical VCSEL results for that.  


This won’t be an issue in actual chip implementation as the skew between the vertical eyes are properly compensated. It could represent another gap for the defined ref. equalizer not able to mimic the product-grade DSP ASICs already available in open market.





From: Jonathan King [mailto:jonathan.king@xxxxxxxxxxx]
Sent: Thursday, August 31, 2017 11:17 AM
To: STDS-802-3-400G@xxxxxxxxxxxxxxxxx
Subject: [STDS-802-3-400G] IEEE P802.3bs TDECQ optimizing eye time centre of eye


Dear colleagues,

Please find attached a short presentation which I hope to review in the 802.3bs face to face meeting in Charlotte, and which describes a proposed change to the TDECQ method which will allow TDECQ to be calculated at the optimum eye timing point, by allowing the histogram time positions to be adjusted for optimum TDECQ.  This change would reflect the capabilities of real world  implementations of receivers with T spaced and T /2 spaced equalizers.


Without this change, the TDECQ definition in the current draft (802.3 D3.3) means that transmitters with equalized eyes which are offset from the time centre of the eye are penalized with higher TDECQ, which would contribute to the decorrelation of Tx TDECQ and measured link performance.


I believe the change is absolutely necessary to prevent unnecessary transmitter TDECQ failures. 


If you are willing to be a supporter of this proposed change please send me an e-mail to let me know your name and affiliation.

Feel free to ask questions of course!


Best wishes

Jonathan King