[SI-LIST] Re: How to place the AC coupling capacitor of the serdes?

Hi Martin=3A

   Thank you =2EThe only reason that we=27ve found now is=3A
   In application such as cable and backplane=2Cit is possible that =

the transimit pair may inadvertently DC biased=2C due to bent pins =

or wrong cable=2Cand this unwanted DC bias may damage the SERDES Driver=2C=

so AC coupling capacitors at the transmitted pairs as well as =

received pairs are required=2E
   Also thanks to Ritchey =2CIvor and Mike=2Cfor your kindly reply=3A)

   Regards=2C

                LIU Luping

  =

 =

Msg=3A =231 in digest
Subject=3A =5BSI-LIST=5D Re=3A How to place the AC coupling capacitor of =
the serdes=3F
Date=3A Fri=2C 18 Jan 2008 08=3A57=3A41 +0100
From=3A =22Bahlinger=2C Martin=22 =3Cmartin=2Ebahlinger=40barco=2Ecom=3E

Hi Liu=2C

Several times I searched for an answer to this question on the web and
could not find any clue=2E I also asked a Gigabit serdes expert on this
subject and all I got was=3A One needs the caps=2C but it does not matter=

whether they are placed at the receiver or at the transmitter=2E

To have some rule on this in the PCIe spec is necessary=2C because quite
often communicating devices are developed by different parties=2E Thus
this rule ensures to not miss the caps on any lane=2E But why they chose
TX and not RX=3F No idea=2E=2E=2E


Regards
Martin


 -----Original Message-----
From=3A si-list-bounce=40freelists=2Eorg =5Bmailto=3Asi-list-bounce=40fre=
elists=2Eorg=5D
On Behalf Of liuluping 41830
Sent=3A Freitag=2C 18=2E Januar 2008 05=3A11
To=3A si-list=40freelists=2Eorg
Cc=3A oukanghua=40huawei=2Ecom
Subject=3A =5BSI-LIST=5D How to place the AC coupling capacitor of the se=
rdes=3F

Dear si-listers=3A
AC coupling per the PCI Express Base Specification Revision 1=2E0a=2C
section 4=2E3=2E1=2E2 dictates AC coupling to be placed as
close as practical to the transmitter buffer=2E=3D20
We consider that the AC cap is used to ensure the DC bias levels of the
transmitted signal do not adversely
affect the receiver=2Cand most of time place it clsoe to the receiver
side=2EWhy the PCIe requires  to put it on the TX side=3F
Is it differ from different serdes interface=3F

 Thanks and Regards=2C

                    LIU Luping


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