[SI-LIST] Re: How to place the AC coupling capacitor of the serdes?
- From: "Bahlinger, Martin" <martin.bahlinger@xxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Fri, 18 Jan 2008 08:57:41 +0100
Hi Liu,
Several times I searched for an answer to this question on the web and
could not find any clue. I also asked a Gigabit serdes expert on this
subject and all I got was: One needs the caps, but it does not matter
whether they are placed at the receiver or at the transmitter.
To have some rule on this in the PCIe spec is necessary, because quite
often communicating devices are developed by different parties. Thus
this rule ensures to not miss the caps on any lane. But why they chose
TX and not RX? No idea...
Regards
Martin
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of liuluping 41830
Sent: Freitag, 18. Januar 2008 05:11
To: si-list@xxxxxxxxxxxxx
Cc: oukanghua@xxxxxxxxxx
Subject: [SI-LIST] How to place the AC coupling capacitor of the serdes?
Dear si-listers:
AC coupling per the PCI Express Base Specification Revision 1.0a,
section 4.3.1.2 dictates AC coupling to be placed as
close as practical to the transmitter buffer.=20
We consider that the AC cap is used to ensure the DC bias levels of the
transmitted signal do not adversely
affect the receiver,and most of time place it clsoe to the receiver
side.Why the PCIe requires to put it on the TX side?
Is it differ from different serdes interface?
Thanks and Regards,
LIU Luping
=20
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