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Re: [802.3_4PPOE] Slide 7

Hi Jeff,

Please see my response below.

Thanks for communicating all these questions over the reflector.






From: Jeff Heath [mailto:jheath@xxxxxxxxxx]
Sent: Tuesday, July 01, 2014 11:02 PM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: [802.3_4PPOE] Slide 7




On slide you again say that the PD PI needs to be better than the PSE PI despite the objections noted in the previous meeting. 

Yair: You are correct, I have already changed it but I didn’t send it together with other updates due to lake of time. The following is what you will see in the next adhoc slides.


  • " Channel capable of regulating/reducing of end to end unbalance as function of channel length.
  • PD PI and PD PI need to be better than the channel maximum P2PRUNB.
  • PSE PI and PD PI needs larger unbalance range to allow different implementations (TBD)

Please let me know if it is OK for you now.  


Specifically to what we know so faron the subject:

-Since in first meetings we agree that the PD is dominant in setting the pair to pair current especially the diode effects, we would like to give the PD flexibility in a way that we will not have to add components to PD and also support Type 1 and 2 PDs that are already in the field.

-The PSE on the other side has different implementations. You can see it by using the current numbers in the data base table in which you create combinations possible resistances in positive rail, negative rail and the mix between them.

-The question which should be higher, I need to finalize my research in order to be sure

Could create a presentation to show why you come to this conclusion.

I will not have time to  put presentation for it for July however I suggest that you will do it so we can decide on this point.  


IF anything, the PSE is much easier to balance (if one does not use AC MPS.)  The standard PD implementation has diode bridges which in the short channel case (at least), are currently thought to be the largest contributor to overall current imbalance.

Yair: I agree with you in principle, but in order to be sure we need to set a list of PSE use case, analyze it and set the conclusions in similar what I am trying to do with the channel use cases.


In short, in the worst case PSE implementation (using AC MPS diodes) twice as many diodes as the PSE which directly opposes the conclusion you have arrived at.

Yair: You may be correct. But we need to follow the way suggested above so we will have records justifying our decisions. Sine you presented yesterday the MPS case, you can generate more use cases, eg. What will happen in 100BT systems and then we will see where it goes. Then we will know for sure. I am mentioning it since I am not sure you cover all use cases (thos you familiar with and those you don’t and you may need to ask for inputs about it)







Jeff Heath
Design Center Manager

Description: Linear Technology Corporation




402 East Carrillo Street, Suite D


Santa Barbara, California 93101