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Re: [802.3_B10GAUTO] AC coupling capacitors information

Hi Haysam,

   The PoDL parameters may be subject to change, as the frequency is scaled up by 2.5X. I anticipate that the PHY parameters RT (nominal 50Ohm, min 45Ohm, max 55Ohm), the parasitic termination capacitance CT of 0.1pF, the coupling capacitance of 10nF will be in the same ball park.

    The MDI insertion loss and the MDI return loss of the PCB will be subject to contributions in the future. For now my comment is  restricted to the change of the  lower frequency limit of  the link segment insertion loss.

    Thank you,

German Feyh

On Wed, Jan 12, 2022 at 8:20 PM George Zimmerman <george@xxxxxxxxxxxxxxxxxxxx> wrote:

What we might consider is under equation 165-25 (and possibly in the informative annex, but I’m not sure where it goes yet, since that isn’t actually a requirement) inserting the following:

NOTE – For testing purposes it is sufficient to test the insertion loss of the link segment from 10 MHz to 9000 MHz and spot-check the insertion loss at 1 MHz. 

 

[or whatever frequency we determine the lower frequency should be].  That should be enough to catch anything that has bad behavior at low frequencies.

 

From: George Zimmerman <george@xxxxxxxxxxxxxxxxxxxx>
Sent: Wednesday, January 12, 2022 4:06 PM
To: STDS-802-3-B10GAUTO@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_B10GAUTO] AC coupling capacitors information

 

Guys, looking at this, I’m coming to the opinion that we have to specify the link segment (equation 165-25) at frequencies lower than 10 MHz.  Not only do the implementation considerations that German has raised apply, but consider the autoneg signal.  Clause 98 autoneg is a 16.7 Mbit DME stream.  Cutting out the lower 10 MHz will kill autoneg. 

 

So, where that leaves us is to write text that keeps the cabling guys from having to set their testers to start at 1 MHz.  Nobody wants that.  Anyone who has done wideband measurements knows that there are several ways around this, generally measuring in more than one pass (one for the low frequencies and one for the rest) but  from a standards perspective they all involve just writing a good informative note.

-george

 

From: German Feyh <gerfeyh@xxxxxxxxx>
Sent: Wednesday, January 12, 2022 3:50 PM
To: STDS-802-3-B10GAUTO@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_B10GAUTO] AC coupling capacitors information

 

Hi Haysam,

 

   George Zimmerman suggested using 1MHz as the lower frequency limit to be consistent with 802.3ch.


   vakilian_3ch_01_0719.pdf in 802.3ch had PHY termination circuit values and board component assumptions for PoDL on slide 4.

 

   Thank you,

 

German Feyh

 

On Tue, Jan 11, 2022 at 7:50 PM Haysam Kadry <hkadry@xxxxxxxx> wrote:

Hello, 

 

The discussion in moving the IL limit from 10MHz to 2MHz in accordance to https://www.ieee802.org/3/cy/public/nov21/feyh_3cy_01b_01_11_09_21.pdf.  I am looking for some information 

 

1. AC couple capacitor value range and ESR characteristics.

2. PHY termination circuit values 

 

This will help put together a simulation profile for the front end circuit.  

 

Best regards, 

 

Haysam M. Kadry

Ford Motor Company

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