[SI-LIST] Re: AC coupling of SATA and SAS I/O
- From: Alief <saifj_m@xxxxxxxxx>
- To: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>, "T.K. Jeon" <tkjeon@xxxxxxxxxxx>
- Date: Thu, 7 May 2009 12:41:23 -0700 (PDT)
Thank you for your response T.K.
Yes, a 0V DC bias would establish an automatic reference (in theory); thus it
would be akin to DC coupling.
However, I am hesitant to make my common mode 0V; because of issues with ground
loops, ground path parasitics, etc and also because the receiver would see
negative voltages.
I realize that this is to first order a biasing issue and allows for
interoperability.
However, are there other considerations ? I have heard/read that it might
permit hot swappability. Is this true. If I had a known common mode level
doesn't that make it easier for hot swapping ?
Also, are there other issues which AC coupling helps with ?
Thanks a bunch in advance,
Alief
--- On Thu, 5/7/09, T.K. Jeon <tkjeon@xxxxxxxxxxx> wrote:
From: T.K. Jeon <tkjeon@xxxxxxxxxxx>
Subject: RE: [SI-LIST] AC coupling of SATA and SAS I/O
To: "Alief" <saifj_m@xxxxxxxxx>, "si-list@xxxxxxxxxxxxx"
<si-list@xxxxxxxxxxxxxx>
Date: Thursday, May 7, 2009, 6:55 PM
Alief,
AC coupling is needed to maintain the correct DC bias for receivers. If your
transmitter has 0V DC bias, then I guess you don't have to implement AC
coupling.
TK
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Alief
Sent: Thursday, May 07, 2009 10:46 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] AC coupling of SATA and SAS I/O
Greetings everyone,
I am currently looking at SATA and SAS SerDes designs. It looks like the data
transmission is AC coupled. Is this a standards requirement ?
Could anyone enlighten me on why SATA/SAS specifies only AC coupled links [if
that is in fact the case]; i.e. what was the thinking/justification for
restricting transmission to ac coupled only.
Also, do the other standards : Gbit Ethernet, PCI Express, RapidIO, etc. have
similar restrictions/requirements ?
Thanks v much in advance,
Alief
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