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 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net <http://www.si-list.net/> List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu