[802.3_4PPOE] Open Circuit Vdiff Test

[Ken <ken_bennett@xxxxxxxxx>]

Hi Yair, All,

I've attached a simulation of a Vdiff open circuit measurement which 
shows a 20mV Vdiff result for an internal current leakage difference of 
10uA.  The implication is that a series forward-biased diode feeding the 
PI can easily fail this conformance test unless it feeds both pairs of 
the same polarity through a common node.

Avoiding any forward-biased diodes which feed a single pair in 4-pair 
PSE designs may be the only practical means to consistently avoid this 
test failure.  This would likewise result in better balance at high 
currents.  However, some AC MPS and protection methods may be impacted 
by this, so a note in an Annex and perhaps removal of AC MPS in 4-pair 
designs might be warranted.

The above points probably do validate the omission of such PSE diodes 
from 4pr unbalance models, which is helpful.

Best Regards,
Ken

Attachment: PSE_Diodes.jpg
Description: JPEG image