[SI-LIST] Re: Board-to-board connectors without reference planes?
- From: Joel Brown <joel@xxxxxxxxxx>
- To: Scott McMorrow <scott@xxxxxxxxxxxxx>
- Date: Wed, 4 Jun 2014 13:19:57 -0700
I did a Qseven design and it worked fine.
There are not many grounds on the connector so it is not ideal and as you
said the differential pairs help.
I am not aware of any high speed single ended signals.
The differential pair interfaces are not running at really high data rates,
I think PCIe at 2.5 GBPS may the fastest.
Since Qseven modules are typically used in small embedded systems the
traces lengths tend to be only a few inches.
The Qseven connector is actually an MXM connector that has been used for
embedded graphics cards.
I can't speak to the signal integrity or EMI because we didn't look at
those but it functioned without any problems.
Joel
On Wed, Jun 4, 2014 at 12:53 PM, Scott McMorrow <scott@xxxxxxxxxxxxx> wrote:
> PCI express uses co-planar ground referencing for the high speed systems.
> Ground pins are adjacent to the differential signal pins on each side.
> I would hope that QSeven did the same.
>
>
> Scott McMorrow
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>
> On Wed, Jun 4, 2014 at 3:40 PM, ckrich_99@xxxxxxxxx <
> dmarc-noreply@xxxxxxxxxxxxx> wrote:
>
> > I know that high-speed signals must be routed with an
> > adjacent reference plane so the current loop area is minimal. We're
> > always told not to cross plane splits on PCBs
> > because this will cause SI/crosstalk and EMI issues.
> > However, I'm working with a QSeven module, which plugs into
> > an edge connector.
> > http://www.qseven-standard.org/
> > The QSeven connector supports very
> > high-speed differential signals like Ethernet, USB, HDMI, LVDS and
> several
> > single-ended buses. Once the module is
> > plugged into a plastic connector, the signals pass through the connector
> > into
> > gold-plated discrete pins which are soldered to the baseboard. However,
> > there's no reference plane for these
> > pins (for at least 6mm), and yet it works fine- how?
> > I've had the same question about PCI Express
> > connectors. They uses only
> > differential-pairs so you can argue the diff-pairs use each other as
> > "returns"
> > if there's no nearby plane. But QSeven
> > also has high-speed single-ended signals.
> > Thanks+ Regards,Richard
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