[SI-LIST] Re: PCI Express capacitor-pack - Email found in subject

We ignored this advice once, we used a dual capacitor pack for PCIe, and we 
lived to regret it. There really is some in-package coupling that kills or 
severely  attenuates the signal. We then loaded discrete 0201 caps instead, and 
the PCIe interface then worked as it should. Use discrete 0402 or 0201 parts.
 
- SM / Kontron
________________________________

From: si-list-bounce@xxxxxxxxxxxxx on behalf of Alexandre Desnoyers
Sent: Fri 8/20/2010 6:46 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] PCI Express capacitor-pack - Email found in subject



Hello everyone,

Maybe someone can shed a bit of light on this.  I've been trying to find a
good explanation for the following requirement in the PCI Express
motherboard checklist:

"Differential signal AC coupling capacitors cannot be Capacitor-packs"
(see reference after my signature)

I fully understand the capacitor-pack crosstalk effect when used for
multiple pairs,
but I've been trying to find any measurements of their effect when a
dual AC coupling
capacitor-pack is used for one pair (P & N).  How does it compare with two
0402 capacitor close together?

Does any of you have made such simulation or measurements?


Thanks

Alexandre Desnoyers
Electronic Design Engineer
Qtechnology A/S


Reference is on page 30 (PCB.01#29) of
http://www.pcisig.com/developers/compliance_program/prod_listreq/PCIeMotherboardChecklist1.1a.doc

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