[SI-LIST] Re: SATA board to board connector question
- From: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
- To: <olaney@xxxxxxxx>
- Date: Mon, 27 Aug 2007 09:57:16 -0700
Hi Orin,
Do you have some specific data on the difference in performance between
microstrip and stripline? While I agree with your first premise (that
stripline introduces the parasitics of the via to get down to the
layer), my studies (see url below) have indicated equal loss between the
2 mediums (stripline vs. microstrip), with the caveat that microstrip
often allows wider traces with resultant lower copper loss. But,
impedance control on the inner layers (with no plating) is usually
better, and crosstalk is reduced.
I've often heard similar arguments to your "snorkeling" metaphor, but
haven't seen data supporting it.
This leads me to favor lower layers of stripline for long lengths of
high-speed signals, when I have a choice (a rare luxury).
Perhaps you've had some other experience or have data to share?
url to my study on microstrip vs. stripline loss:
http://pcdandm.com/cms/content/view/2572/95/
Note to all: there have been many postings on "Microstrip vs. Stripline"
on this forum, worthy of perusing if you're interested.
Disclaimer:
The content of this message is my personal opinion only and although I
am an employee of Intel, the statements I make here in no way represent
Intel's position on the issue, nor am I authorized to speak on behalf of
Intel on this matter.
Jeff Loyer
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of olaney@xxxxxxxx
Sent: Monday, August 27, 2007 8:56 AM
To: nareshd@xxxxxxxxxxxxx
Cc: goister@xxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: SATA board to board connector question
Usually I prefer microstrip over stripline for signals as fast as SATA.=20
The reasoning boils down to two considerations. One is that transitions
between buried stripline and other layers brings its own set of
problems,
and the other is that in a world where (censored) insist on using FR4 in
the microwave region, the less contact a high speed signal has with the
stuff, the better. Air is a reasonable microwave dielectric. The FR in
FR4 means "fire retardent", which is not a microwave concept.
Microstrip
steps in the poop on only one side of the trace, where stripline is like
snorkling in it. This makes a difference in how much signal quality
gets
eaten per unit length.
Don't get me wrong. Stripline is excellent microwave practice when
proper dielectrics are used and connectorization is competently
implemented. But, that level of attention seems reserved for a
different
world filled with directional couplers, 90 degree hybrids, and other
exotic animals never seen on this forum.
Orin
On Mon, 27 Aug 2007 15:43:26 +0530 "Dhamija Naresh-B07930"
<nareshd@xxxxxxxxxxxxx> writes:
> I also have a Question related to SATA signal routing in PCB.
>=20
> Which routing is the best for SATA signals - On Outer Layers OR=20
> in
> inner layers.
> I am finding the difference in performances of two.
>=20
> - Naresh
>=20
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx=20
> [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
>=20
> Thanks. One more question. You mention to carry the ground pins=20
> 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=20
> connector,
> and rely solely on the signal connector to provide the ground plane=20
> for
> the daughterboard?
> On 8/24/07, olaney@xxxxxxxx <olaney@xxxxxxxx> wrote:
> >
> > Separate power is the usual approach, and not a problem. Some of=20
> the
>=20
> > smaller Samtec connectors sound like a good choice for constant Z=20
>=20
> > board to board, among many others. Most formal backplane=20
> connectors=20
> > probably have way too many pins for your need. It looks like you=20
> have
>=20
> > everything on track for a successful design. Keep the list posted=20
> 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"=20
> <goister@xxxxxxxxx>
> writes:
> >
> > Thanks.
> >
> > Basically the daughterboard acts simply as kind of an extender of=20
> the=20
> > SATA signal. So all the logic circuitry is on the main board, with=20
> the
>=20
> > SATA signals coming out of the SATA controller chip, and to the=20
> > daughter board via the high speed connector direct(no cables).=20
> These=20
> > signals are then routed to an actual SATA HDD 7pin connector on=20
> the=20
> > daughterboard, to be connected to a SATA HDD. SATA power to the=20
> HDD=20
> > will most likely be routed with another connector, probably a=20
> regular=20
> > pin header/socket. That shouldn't be a problem right?
> >
> > Regarding the fat pads, I'll probably be using 0402 components as=20
> much
>=20
> > as possible to reduce this problem, particularly for the 10nF=20
> > capacitors required for the SATA signals. I believe this is part=20
> of=20
> > the SATA recommendations too.
> >
> > On 8/24/07, olaney@xxxxxxxx <olaney@xxxxxxxx> wrote:
> > >
> > > Yes, the connector manufacturer recommendations. Any connector=20
>=20
> > > with the right impedance and adequate data rate specs will do. =20
> The=20
> > > same connector family can be used for many purposes, so it is=20
> 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=20
> or=20
> > > used for other purposes. I don't know if you are trying to=20
> connect=20
> > > your boards connector to connector direct, or through a short=20
> cable.
>=20
> > > In any instance, keep the I/O chip close to the connector, and=20
> avoid
>=20
> > > changes in trace widths other than what might be recommended for=20
>=20
> > > dealing with proximity effects (sometimes the signal traces are=20
>=20
> > > tapered where they run under connector dielectric). One common=20
>=20
> > > signal integrity killer is where the traces are carefully=20
> designed,=20
> > > yet run through coupling caps or other passives using the fat=20
> SMT=20
> > > pads that production loves so much. Sometimes production balks=20
> at=20
> > > the practice of using wider traces or narrower parts to minimize=20
> the
>=20
> > > discontinuity in microstrip width. Given the choice between a=20
> > > design that works and one that can be built without hand=20
> 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,=20
> as=20
> > > crosstalk can be controlled with adequate pair separation. I=20
> would=20
> > > not assume that a 7 pin connector is the goal. Think of it as=20
> two=20
> > > impedance controlled pairs plus whatever ground paths are=20
> designed=20
> > > in to ensure impedance and crosstalk control. The ground need=20
> not=20
> > > be discrete pins on par with the signals, in the same way that a=20
>=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=20
> the=20
> > > signals through the same connector!!! Any ground connections=20
> > > provided elsewhere in the system might make an ohmmeter happy,=20
> but
> relying on them =3D death at high frequencies.
> > >
> > > Molex might be another vendor to include in your list. Don't be=20
> shy
>=20
> > > about using vendor field app engineers -- that's what they're=20
> paid=20
> > > for, and it's job security for them.
> > >
> > > Orin
> > >
> > > On Thu, 23 Aug 2007 23:07:46 +0800 "Sihan Goi"=20
> <goister@xxxxxxxxx>
> > > writes:
> > >
> > > Thanks. It's kinda confusing when I go to samtec, FCI or=20
> amphenol=20
> > > website and they don't show what kind of applications the high=20
> speed
>=20
> > > connectors are meant for, or their impedance rating or=20
> whatever...
> > >
> > > Anyway, I'm also wondering about how the signals should be=20
> routed to
>=20
> > > the connector. SATA signals on regular SATA connector are as=20
> follows
>=20
> > > GND A+ A- GND B+ B- GND
> > >
> > > Should I be following this topology or does it even matter? I'm=20
>=20
> > > guessing most of these high speed connectors won't have exactly=20
> 7=20
> > > pins. They're usually spec'ed for 2/3/4 pairs or even more. I'm=20
>=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
>=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=20
> go=20
> > > > for 5 GHz or more of frequency response. Biggest headache=20
> tends=20
> > > > to be keeping the impedance constant where the traces enter=20
> the=20
> > > > connector launch area.
> > > > Pay attention to the manufacturer recommendations.
> > > >
> > > > Orin Laney
> > > >
> > > > On Thu, 23 Aug 2007 16:08:09 +0800 "Sihan Goi"=20
> <goister@xxxxxxxxx>
> > > > writes:
> > > > > Hi,
> > > > > I have a design where I have to route SATA signals from a=20
> main=20
> > > > > board to a daughter board. The daughter board will likely=20
> have=20
> > > > > nothing except for the 7 SATA signals(4 data and 3 GND)=20
> > > > > connected to a regular SATA HDD connector (unless some=20
> 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=20
> for=20
> > > > > PATA. I'm guessing this will not work so well with SATA=20
> 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
>=20
> > > > > difference must be within 5 mils. I'm guessing I have to get=20
> a=20
> > > > > high speed connector that has the same impedance and is able=20
> to=20
> > > > > support 3GHz speeds? Is that all I need to be looking for?
> > > > >
> > > > > Thanks.
> > > > >
> > > > > --
> > > > > - Goi Sihan
> > > > > goister@xxxxxxxxx
> > > > >
> > > > >
> > > > >=20
> ----------------------------------------------------------------
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> > > --
> > > - Goi Sihan
> > > goister@xxxxxxxxx
> > >
> > >
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> > --
> > - Goi Sihan
> > goister@xxxxxxxxx
> >
> >
>=20
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> --
> - Goi Sihan
> goister@xxxxxxxxx
>=20
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