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

  • From: "Sihan Goi" <goister@xxxxxxxxx>
  • To: "olaney@xxxxxxxx" <olaney@xxxxxxxx>
  • Date: Mon, 27 Aug 2007 18:03:41 +0800

Thanks. One more question. You mention to carry the ground pins together
with the signals on the same connector. Why is this so? I do have another
connector that carries the power signals. Does this mean I should not route
any other ground signal(s) with this power connector, and rely solely on the
signal connector to provide the ground plane for the daughterboard?
On 8/24/07, olaney@xxxxxxxx <olaney@xxxxxxxx> wrote:
>
>  Separate power is the usual approach, and not a problem.  Some of the
> smaller Samtec connectors sound like a good choice for constant Z board to
> board, among many others.  Most formal backplane connectors probably have
> way too many pins for your need.  It looks like you have everything on track
> for a successful design.  Keep the list posted on the more significant
> problems and progress, so that everybody can learn from your experience.
> And make those app engineers take you out to lunch.
>
> Regards,
>          Orin
>
> On Fri, 24 Aug 2007 12:07:16 +0800 "Sihan Goi" <goister@xxxxxxxxx> writes:
>
> 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
> > > >
> > > >
> > > > ------------------------------------------------------------------
> > > > To unsubscribe from si-list:
> > > > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject
> > > > field
> > > >
> > > > or to administer your membership from a web page, go to:
> > > > //www.freelists.org/webpage/si-list
> > > >
> > > > For help:
> > > > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> > > >
> > > >
> > > > List technical documents are available at:
> > > >                 http://www.si-list.net
> > > >
> > > > List archives are viewable at:
> > > >                 //www.freelists.org/archives/si-list
> > > > or at our remote archives:
> > > >                 http://groups.yahoo.com/group/si-list/messages
> > > > Old (prior to June 6, 2001) list archives are viewable at:
> > > >                  http://www.qsl.net/wb6tpu
> > > >
> > > >
> > > >
> > > >
> > >
> >
> >
> >
> > --
> > - Goi Sihan
> > goister@xxxxxxxxx
> >
> >
>
>
> --
> - Goi Sihan
> goister@xxxxxxxxx
>
>


-- 
- Goi Sihan
goister@xxxxxxxxx


------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field


List technical documents are available at:
                http://www.si-list.net

List archives are viewable at:     
                //www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu
  

Other related posts: