[SI-LIST] Re: PCI Express AC Coupling

Chris,
regarding signal integrity implications you may want to look up the list 
archive. There has been a very extensive thread about this a few months 
ago, and there were a few others as well that I can recall. In a nutshell, 
well-designed AC coupling - both with regarrds to component choice and 
with regards to layout/landing pattern will be transparent to the signal 
up to many GHz, so in theory you can put additional DC blocks in your path 
at will. Of course such a design is not trivial for higher data rates (but 
it can be done).

Wolfgang










Chris Johnson <cjohnson@xxxxxxx> 
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03/10/2010 01:36 PM

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[SI-LIST] PCI Express AC Coupling






Could someone tell me if any of the TX (from motherboard to card), RX 
(from card to motherboard), and REFCLK (from motherboard to card) PCI 
Express differential pairs are guaranteed to be AC coupled on the 
motherboard?

Also, is there significant signal integrity downside to AC coupling on 
the plug in card, when the signals are already AC coupled on the 
motherboard, assuming that the AC coupling is right at the I/Os to the 
chip on the plug in card?

Thanks,

Chris

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