[SI-LIST] AW: Questions on 10GBase-KX/KX4/KR

  • From: "Havermann, Gert" <Gert.Havermann@xxxxxxxxxxx>
  • To: "qinzhenshui@xxxxxxxxxxx" <qinzhenshui@xxxxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
  • Date: Fri, 16 Mar 2012 09:34:20 +0000

Hi Bruce,

The caps are excluded for two reasons:
- because they can mask channel performance
- Test fixtures are designed without caps (for several reasons)

The Annex 69B is for compliance testing rather than simulation, thus excluding 
caps in the Spec. does make sense. You should also start passive Channel 
simulations without caps (S-Parameter simulations). For active channel 
simulations (BER, Eye...) you should include caps and vias. For Backplane 
vendors like us, This is hard to do, as the via setup isn't known, but for 
Blade designers this shouldn't be an issue.
The caps do not have the biggest impact, it's the vias that do most harm.

The fitted ICR makes more sense than the raw ICR because the digital signals 
are broadband in nature. If you find a small ICR violation, e.g. in the area of 
3GHz-3.2GHz, this will not kill your system, it will just slightly change the 
rising and falling edges of some of the bits. When the violations get wider in 
frequency, then the impact increases, and the fitted curve will start to show 
violations, and you might loose some bits. Therefore the fitted ICR is more 
robust to violations, while still achieving functionality.

BR
Gert


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-----Ursprüngliche Nachricht-----
Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] Im 
Auftrag von QinBruce
Gesendet: Freitag, 16. März 2012 07:40
An: si-list@xxxxxxxxxxxxx
Betreff: [SI-LIST] Questions on 10GBase-KX/KX4/KR

Hi Experts.

I have two questions regarding 10GBase-KX/KX4/KR spec defined in Annex 69B 
IEEE802.3ap.
1. External AC-coupling capacitors are excluded from the defined backplane 
channel, so does it mean it's not need to consider these capacitors in my 
channel simulation?
My idea is the capacitors have great impact on the channel performance, so we 
are not modeling the whole channel with them excluded. Am I right?
2. Why define the ICR as least mean square fitted curve rather not the raw ICR? 
And why it is started at 100MHz?

Thanks in advance.
Bruce

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  • » [SI-LIST] AW: Questions on 10GBase-KX/KX4/KR - Havermann, Gert