[SI-LIST] Re: PCI Express AC Coupling
- From: "Michael Rose" <mrose@xxxxxxxxxxxx>
- To: "Chris Johnson" <cjohnson@xxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Wed, 10 Mar 2010 17:46:36 -0500
Chris, I thought PCIe required AC coupling on both ends(?). Generally, I
like to place the coupling caps on the RX end since the channel
attenuates the slew rate making the impedance discontinuity a bit less
severe. In some cases, AC coupling on both ends has the advantage of
tolerating a short circuit through the interconnect without damaging the
driver.
Mike
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Chris Johnson
Sent: Wednesday, March 10, 2010 4:37 PM
To: si-list@xxxxxxxxxxxxx
Subject: [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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