AC Coupling Caps, sizing?

William Gintz wcgintz at ix.netcom.com
Mon Oct 25 03:15:44 PDT 2004


* From the T10 Reflector (t10 at t10.org), posted by:
* William Gintz <wcgintz at ix.netcom.com>
*
Rob...following , I think, your thread..

1. Some caution is recommended in specifying an AC coupling cap size.
Whereas FC drives, phy layers & PLL's are pretty immune, SATA 's
compatibility demands a transient response to reliably detect OOB bursts.
  Those not employing  such "beer budget drives" read no further.

2. I  regret that this was not clearly defined in the original SATA 1 specs.
Hopefully it will be duly noted in evolving SATA I/O 2 specifications!
..also note its particularly important for extreme voltage swings which
could exceed the common mode range of low voltage, narrow poly, ASICs.
...Compounded by some mixed ac & dc devices. ... hopefully you're way
  ahead and your crisp rules take this into account...I'd have to diagram use
models  with caps sized, then run sims to be comfortable.
........Bigger coupling caps ain't (no longer )necessarily better!............

  3. Free advice...worth what you paid!

Bill

P.S. We, Dan Smith , Bill  Lye  & I  are trying to agree on some free-ware to
  illustrate this sort of issue without disclosing proprietary methods or ASIC
internal properties.  We'd probably share if you do, maybe at T 10 in Austin.

Bill Bissonette (Intel) has presented quite satisfactory simulation data in SAS
  WGs, but likely cannot share soft ware with all others so that they can 
verify
their own configurations and demons out of public scrutiny. I hope he will
join us in a publicly verifiable  forum.

At 10:58 AM 10/20/2004, Elliott, Robert (Server Storage) wrote:
>* From the T10 Reflector (t10 at t10.org), posted by:
>* "Elliott, Robert (Server Storage)" <elliott at hp.com>
>*
>These are the rules in SAS:
>
>"For all inter-enclosure TxRx connections, the transmitter shall be A.C.
>coupled to the interconnect through a transmission network.
>
>For intra-enclosure TxRx connections the expander transmitter shall be
>A.C. coupled to the interconnect. Other transmitters may be A.C. or D.C.
>coupled.
>
>The receiver shall be A.C. coupled to the interconnect through a receive
>network."
>
>The "expander transmitter" term is a bit misleading.  Think of the rules
>as:
>* All receivers need capacitors.
>* Transmitters behind an external connector need capacitors.
>* Transmitters behind an internal connector that might attach to SATA
>drives need capacitors.
>* Transmitters behind an internal connector that do not attach to SATA
>drives may forgoe capacitors.
>
>
>--
>Rob Elliott, elliott at hp.com
>Hewlett-Packard Industry Standard Server Storage Advanced Technology
>https://ecardfile.com/id/RobElliott
>
>
>
>
> > -----Original Message-----
> > From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf
> > Of Sal Perez
> > Sent: Wednesday, October 20, 2004 8:43 AM
> > To: t10 at t10.org
> > Subject: AC Coupling Caps
> >
> >
> > * From the T10 Reflector (t10 at t10.org), posted by:
> > * Sal Perez <perez6991 at yahoo.com>
> > *
> > --0-274646554-1098279772=:20930
> > Content-Type: text/plain; charset=us-ascii
> >
> > Hi All,
> > I design a SAS backplane that supports 4 hard drives.  The
> > backplane is cabled to a SAS PCI-X add-in card and hard
> > drives are plugged  into the backplane.  On the SAS
> > backplane, do I need to have AC coupling caps on the TX and
> > RX lines? Or are the AC coupling caps required on the SAS
> > PCI-X add-in card?
> >
> > Thank a lot,
> > Sal
> >
> >
> > ---------------------------------
> > Do you Yahoo!?
> > Yahoo! Mail Address AutoComplete - You start. We finish.
> > --0-274646554-1098279772=:20930
> > Content-Type: text/html; charset=us-ascii
> >
> > <DIV>Hi All,<BR>I design a SAS backplane that supports 4 hard
> > drives.&nbsp; The backplane is cabled to a SAS PCI-X add-in
> > card and hard drives are plugged&nbsp; into the
> > backplane.&nbsp; On the SAS backplane, do I need to have AC
> > coupling caps on the TX and RX lines? Or are the AC coupling
> > caps required on the SAS PCI-X add-in card?</DIV>
> > <DIV>&nbsp;</DIV>
> > <DIV>Thank a lot,<BR>Sal</DIV><p>
> >               <hr size=1>Do you Yahoo!?<br>
> > <a
> > href="http://us.rd.yahoo.com/mail_us/taglines/aac/*http://prom
>otions.yahoo.com/new_mail/static/ease.html">> Yahoo! Mail Address
>AutoComplete - You start. We finish.
> > --0-274646554-1098279772=:20930--
> >
> > *
> > * For T10 Reflector information, send a message with
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regards,

W.C. Gintz
SEUS, Inc
wcgintz at ix.netcom.com
office    650 494 0335
mobile  650 799 6622  

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