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

  • From: "Dhamija Naresh-B07930" <nareshd@xxxxxxxxxxxxx>
  • To: <goister@xxxxxxxxx>, <olaney@xxxxxxxx>
  • Date: Mon, 27 Aug 2007 15:43:26 +0530

I also have a Question related to SATA signal routing in PCB.

Which routing is the best for SATA signals  -  On Outer Layers OR in
inner layers.
I am finding the difference in performances of two.

- Naresh

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Sihan Goi
Sent: Monday, August 27, 2007 3:34 PM
To: olaney@xxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: SATA board to board connector question

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=20
> board to board, among many others.  Most formal backplane connectors=20
> 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=20
> 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=20
> 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=20
> daughter board via the high speed connector direct(no cables). These=20
> signals are then routed to an actual SATA HDD 7pin connector on the=20
> daughterboard, to be connected to a SATA HDD. SATA power to the HDD=20
> will most likely be routed with another connector, probably a regular=20
> 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=20
> capacitors required for the SATA signals. I believe this is part of=20
> the SATA recommendations too.
>
> On 8/24/07, olaney@xxxxxxxx <olaney@xxxxxxxx> wrote:
> >
> >  Yes, the connector manufacturer recommendations.  Any connector=20
> > with the right impedance and adequate data rate specs will do.  The=20
> > same connector family can be used for many purposes, so it is not a=20
> > matter of the signaling system used as much as the electrical=20
> > performance and the mechanical need.  Extra pins can be ignored or=20
> > used for other purposes.  I don't know if you are trying to connect=20
> > 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=20
> > dealing with proximity effects (sometimes the signal traces are=20
> > tapered where they run under connector dielectric).  One common=20
> > signal integrity killer is where the traces are carefully designed,=20
> > yet run through coupling caps or other passives using the fat SMT=20
> > pads that production loves so much.  Sometimes production balks at=20
> > the practice of using wider traces or narrower parts to minimize the

> > discontinuity in microstrip width.  Given the choice between a=20
> > design that works and one that can be built without hand operations=20
> > 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=20
> > understand them electrically before widening your search.  The=20
> > GSSGSSG layout is not absolutely necessary for short distances, as=20
> > crosstalk can be controlled with adequate pair separation.  I would=20
> > not assume that a 7 pin connector is the goal.  Think of it as two=20
> > impedance controlled pairs plus whatever ground paths are designed=20
> > in to ensure impedance and crosstalk control.  The ground need not=20
> > be discrete pins on par with the signals, in the same way that a=20
> > coax shield is not carried by a pin like that of the center=20
> > conductor.  However, make sure that the ground is carried with the=20
> > signals through the same connector!!!  Any ground connections=20
> > provided elsewhere in the system might make an ohmmeter happy, but
relying on them =3D 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=20
> > 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=20
> > 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=20
> > guessing most of these high speed connectors won't have exactly 7=20
> > pins. They're usually spec'ed for 2/3/4 pairs or even more. I'm=20
> > guessing I only need a 2 pair connector since I only have 2=20
> > differential SATA signal pairs. I'm wondering if I even need to=20
> > 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=20
> > > for 5 GHz  or more of frequency response.  Biggest headache tends=20
> > > to be keeping the impedance constant where the traces enter the=20
> > > 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=20
> > > > board to a daughter board. The daughter board will likely have=20
> > > > nothing except for the 7 SATA signals(4 data and 3 GND)=20
> > > > connected to a regular SATA HDD connector (unless some passives=20
> > > > are needed?).
> > > >
> > > > In my previous PATA design, I used a normal 44pin IDE type=20
> > > > connector pair(pin header + socket), and this worked well for=20
> > > > PATA. I'm guessing this will not work so well with SATA though.=20
> > > > What kind of connectors would work for SATA1/2? I know the=20
> > > > differential impedance is 100ohms, and that the trace length=20
> > > > difference must be within 5 mils. I'm guessing I have to get a=20
> > > > high speed connector that has the same impedance and is able to=20
> > > > 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
>
>


--
- Goi Sihan
goister@xxxxxxxxx


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