Hi Matt,
For “noise enhancement”, I agree TX FFE does not enhance noise as RX FFE - simply because FFE input noise is much less. There is a performance tradeoff analysis on page #11 of
sun_100GEL_01b_0118. Other factors, e.g. TX signal amplitude and circuit distortion are also important. FFE tail tap weight are usually small, therefore the performance difference
of TX/RX FFE regarding noise enhancement and TX signal swing are small.
We see simulations based on linear model in this group showing “comparable” performance results. (I am sure Adee has more comments on choosing the word “Comparable”). Regarding circuit distortion, at this high speed it is critical to
system (especially receiver) performance but not modeled in simulators like COM. That is why we brought some silicon and circuit simulation results to the group. TX FFE approach simplifies receiver for better/easier circuit linearity/bandwidth.
Indeed TX FFE adaptation interface is relatively new to 802.3 (compared to e.g. wireless applications). Hopefully we can make right decisions whether it can be solved by clever ways and whether it can be justified by power saving.
Regards,
Phil
From: Matt Traverso (mattrave) <00000c0cf767a86d-dmarc-request@xxxxxxxx>
Sent: Thursday, September 6, 2018 6:41 PM
To: STDS-802-3-100GEL@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_100GEL] Presentations Uploaded for Sept Interim
Hi Adee, Phil, Adam,
Unfortunately, I won’t be able to join everyone in Spokane, but I wanted to ask about your presentation,
ran_3ck_01_0918.
Quoting slide 3 bullet 2:
“The performance of a long transmitter FFE is comparable to that of a similar FFE in the receiver.”
I am struggling to understand this statement. Textbooks on linear equalizers are pretty clear – noise enhancement is an inherent consequence of how linear equalizers operate. (see link from Hall –
google books link) At the TX, the noise/jitter is inherently less as the signal has yet to transit the channel. So for channels with noise and jitter I think it is clear that a similar length TX FFE has some performance advantage over an RX FFE provided
the back channel from the RX to the TX is good.
I agree with your assertions on the complexity involved in implementing such a back channel for pluggable modules – this will be challenging to specify. I am not sure that the power efficiency benefit is sufficient
to warrant the complexity, but I think it is a good exercise for the task force to examine.
Thanks
--matt
|
From: Elizabeth Kochuparambil (edonnay) <00000b6647231c5d-dmarc-request@xxxxxxxx>
Sent: Thursday, September 6, 2018 4:28 PM
To: STDS-802-3-100GEL@xxxxxxxxxxxxxxxxx
Subject: [802.3_100GEL] Presentations Uploaded for Sept Interim
Hello All –
I have the presentations posted to our website:
http://www.ieee802.org/3/ck/public/18_09/
I owe you 2 things in the next couple of days, but thought I would post this sooner rather than later:
- Agenda – with presentation order
- COM and package models referenced
I will see you in Spokane! We will begin at 8am on Wednesday in Marie Antoinette room (same room .3cd is on Tuesday). Additional logistics and the schedule for next week’s interim can be found here:
http://ieee802.org/3/interims/sept18/schedule.html
~Beth
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