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RE: PMC Spec - Characteristic Impedance Numbers?
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- Subject: RE: PMC Spec - Characteristic Impedance Numbers?
- From: "Ingraham, Andrew" <Andrew.Ingraham@compaq.com>
- Date: Fri, 26 Oct 2001 08:20:54 -0400
- Resent-Date: Fri, 26 Oct 2001 05:38:36 -0700
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- Thread-Topic: PMC Spec - Characteristic Impedance Numbers?
> Is there a proposal to set an impedance target for ... any of the
> other PCI module standards?
> (PCI cards are 62 ohms..)
The unloaded characteristic impedance requirement for regular PCI add-in
cards is 60-100 ohms. I have seen proposed ECRs that would change this
to 51-100 ohms (only when Cin of the IC on the end of the trace is <=
8pF), and an older one that suggested 50-70 ohms.
For PCI-X add-in cards, the corresponding requirement is 57 ohms +/- 10%
(51.3-62.7 ohms). It extends lower than the PCI range for add-in cards,
but PCI-X also requires a smaller maximum device Cin.