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Re: [802.3_4PPOE] End to End Channel Pair to Pair Unbalance Ad Hoc Presentation - More comments/questions from Yair

Hi Jeff,


In addition to my comments in the previous mail, please find additional comments/questions:



Please use adhoc database numbers and adhoc model so we can compare to other work done on the subject this was part of the adhoc effort to generate common database.

Moreover, it will ensure that you are not missing important issues that already covered and detected by previous work.

If you want to suggest different numbers to the database it is OK, but for the purpose of the adhoc work please use what is agreed at the adhoc. In parallel we can discuss over the reflector or at the meeting (if it will be asked to be in the agenda) a request for changes.


Slide 3: 

-Please add after slide 3, a table with all model component values and mark what is different from the adhoc table.

-What is the load type in the model? Is it current source constant power sink? It should be constant power sink otherwise you will get errors regarding maximum current over pair as function of channel resistance.

-What are the components values that were used in the simulated model?


Slide 6: Delta resistance and delta voltages is not sufficient to uniquely specify the PSE PI. You have to do the math to see it. Start with the easy case of Delta voltage=0. You have now only delta resistance. At this point it is clear the current unbalance at short channel (OR THE MAXIMUM CURRENT OF A PAIR)  is not depend only on |Rmax-Rmin|. It depends also on the SUM of (Rmax+Rmin).

Part of the reasons why you don’t see why Delta Resistance is not sufficient is that you need to do the 3rd bullet in slide 13.   


Slide 7: Component value numbers: From adhoc table or different?


Slide 9: The numbers 0.78 ohms and 0.38 ohms are based on different numbers than used by adhoc. The numbers you have used based on slide 28 is incorrect per the way you explained it in slide 39.

I saw in slide 28 where you use 130miliom and 90miliom that can't be. The difference between Rmax and Rmin in transformer is 5% max. I saw in slide 39 that you took values from different temperatures! It is incorrect. Rmax and Rmin need to be at the same temperature. Please use adhoc numbers and if you believe that we need to use different numbers please discuss it over the reflector so we can evaluate if it should be discussed at the adhoc meeting.


Slide 11:

-I was expecting to total 600mA at the PD at PD power of 25.5W. How we can see it from the data?

-In addition I was expecting to have >300mA on the pair with maximum current at a 12.5 ohm loop. Why we don’t see it?

-Please add to the graph the parameters used to run the simulation.


Slide 15 is identical to slide 11. What is the reason for it?

Slide 16: What is the differences between the two curves. Please add legend, titles etc.

Slide 17:

-What is the differences between the four curves. Please add legend, titles etc.

-Suggesting different diode model for low currents makes sense. At low current we get much better results.


Slide 18: Is identical to slide 3.

Slide 21 is identical to slide 5:

Slide 24: What is V1?

Slide 25: If you want to address AC MPS then there are implementations with AC MPS on the positive rail. I am not sure that I know of AC-MPS used in 4P system but could be with very old systems.

Slide 26: Is identical to slide 7.

Slide 28: Transformer data is incorrect. It is 130 and 120milOhms. Please use adhoc database numbers. Connector Rmax should be 0.06ohm and not 0.2 ohms for worst case analysis. See adhoc numbers and rational.

Slide 29, Slide 30: Why we care about if MOSFET is on positive or negative ide at all? Not clear why it is relevant at all?

Slide 31: Is identical to slide 9

Slide 35: Is identical to slide 16

Slide 35: Is identical to slide 17

Slide 40: You said that you got larger numbers for diode resistance. So what you suggest? (for worst case we need the lower numbers).

Slide 41: Yes we need to discuss it. How you got the realistic results and the pessimistic results. Please send more info so we can start discussions over the reflector.


Hope it helps.




From: Jeff Heath [mailto:jheath@xxxxxxxxxx]
Sent: Saturday, June 28, 2014 1:51 AM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: [802.3_4PPOE] End to End Channel Pair to Pair Unbalance Ad Hoc Presentation




Here is the material I will be presenting in next Tuesday’s ad hoc.  Clearly there will not be time to go over all of the material in the 20 minutes allocated.  Therefore I will be covering the methodology, the PSE and PD PIs,  and Link Segment, or Channel, briefly and sharing some preliminary simulation results.




Jeff Heath
Design Center Manager

Description: Linear Technology Corporation




402 East Carrillo Street, Suite D


Santa Barbara, California 93101