[SI-LIST] Re: SATA board to board connector question

  • From: "Sihan Goi" <goister@xxxxxxxxx>
  • To: "olaney@xxxxxxxx" <olaney@xxxxxxxx>
  • Date: Fri, 24 Aug 2007 12:07:16 +0800

Thanks.
Basically the daughterboard acts simply as kind of an extender of the SATA
signal. So all the logic circuitry is on the main board, with the SATA
signals coming out of the SATA controller chip, and to the daughter board
via the high speed connector direct(no cables). These signals are then
routed to an actual SATA HDD 7pin connector on the daughterboard, to be
connected to a SATA HDD. SATA power to the HDD will most likely be routed
with another connector, probably a regular pin header/socket. That shouldn't
be a problem right?

Regarding the fat pads, I'll probably be using 0402 components as much as
possible to reduce this problem, particularly for the 10nF capacitors
required for the SATA signals. I believe this is part of the SATA
recommendations too.

On 8/24/07, olaney@xxxxxxxx <olaney@xxxxxxxx> wrote:
>
>  Yes, the connector manufacturer recommendations.  Any connector with the
> right impedance and adequate data rate specs will do.  The same connector
> family can be used for many purposes, so it is not a matter of the signaling
> system used as much as the electrical performance and the mechanical need.
> Extra pins can be ignored or used for other purposes.  I don't know if you
> are trying to connect your boards connector to connector direct, or through
> a short cable.  In any instance, keep the I/O chip close to the connector,
> and avoid changes in trace widths other than what might be recommended for
> dealing with proximity effects (sometimes the signal traces are tapered
> where they run under connector dielectric).  One common signal integrity
> killer is where the traces are carefully designed, yet run through coupling
> caps or other passives using the fat SMT pads that production loves so
> much.  Sometimes production balks at the practice of using wider traces or
> narrower parts to minimize the discontinuity in microstrip width.  Given the
> choice between a design that works and one that can be built without hand
> operations or other accommodations, they have a tough time making up their
> minds.  As an engineer with proper test equipment and adequate time (That's
> all of us, right?  Right?), you can often meet both goals.
>
> Anyway, you might as well check out formal SATA connectors to understand
> them electrically before widening your search.  The GSSGSSG layout is not
> absolutely necessary for short distances, as crosstalk can be controlled
> with adequate pair separation.  I would not assume that a 7 pin connector is
> the goal.  Think of it as two impedance controlled pairs plus whatever
> ground paths are designed in to ensure impedance and crosstalk control.  The
> ground need not be discrete pins on par with the signals, in the same way
> that a coax shield is not carried by a pin like that of the center
> conductor.  However, make sure that the ground is carried with the signals
> through the same connector!!!  Any ground connections provided elsewhere in
> the system might make an ohmmeter happy, but relying on them = death at high
> frequencies.
>
> Molex might be another vendor to include in your list.  Don't be shy about
> using vendor field app engineers -- that's what they're paid for, and it's
> job security for them.
>
> Orin
>
> On Thu, 23 Aug 2007 23:07:46 +0800 "Sihan Goi" <goister@xxxxxxxxx> writes:
>
> Thanks. It's kinda confusing when I go to samtec, FCI or amphenol website
> and they don't show what kind of applications the high speed connectors are
> meant for, or their impedance rating or whatever...
>
> Anyway, I'm also wondering about how the signals should be routed to the
> connector. SATA signals on regular SATA connector are as follows
> GND A+ A- GND B+ B- GND
>
> Should I be following this topology or does it even matter? I'm guessing
> most of these high speed connectors won't have exactly 7 pins. They're
> usually spec'ed for 2/3/4 pairs or even more. I'm guessing I only need a 2
> pair connector since I only have 2 differential SATA signal pairs. I'm
> wondering if I even need to route the GND with the high speed connector or
> can it be from another regular connector somewhere else...?
>
> Lastly, when you say "pay attention to the manufacturer recommendations"
> which manufacturer do you mean? The connector manufacturer?
>
> Again, thanks for your reply!
>
> On 8/23/07, olaney@xxxxxxxx <olaney@xxxxxxxx> wrote:
> >
> > Basically, yes, but give your design some margin.  For 3 Gb/s go for 5
> > GHz  or more of frequency response.  Biggest headache tends to be
> > keeping
> > the impedance constant where the traces enter the connector launch area.
> >
> > Pay attention to the manufacturer recommendations.
> >
> > Orin Laney
> >
> > On Thu, 23 Aug 2007 16:08:09 +0800 "Sihan Goi" <goister@xxxxxxxxx>
> > writes:
> > > Hi,
> > > I have a design where I have to route SATA signals from a main board
> > > to a
> > > daughter board. The daughter board will likely have nothing except
> > > for the 7
> > > SATA signals(4 data and 3 GND) connected to a regular SATA HDD
> > > connector
> > > (unless some passives are needed?).
> > >
> > > In my previous PATA design, I used a normal 44pin IDE type connector
> > > pair(pin header + socket), and this worked well for PATA. I'm
> > > guessing this
> > > will not work so well with SATA though. What kind of connectors
> > > would work
> > > for SATA1/2? I know the differential impedance is 100ohms, and that
> > > the
> > > trace length difference must be within 5 mils. I'm guessing I have
> > > to get a
> > > high speed connector that has the same impedance and is able to
> > > support 3GHz
> > > speeds? Is that all I need to be looking for?
> > >
> > > Thanks.
> > >
> > > --
> > > - Goi Sihan
> > > goister@xxxxxxxxx
> > >
> > >
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>
>
> --
> - Goi Sihan
> goister@xxxxxxxxx
>
>


-- 
- Goi Sihan
goister@xxxxxxxxx


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