[SI-LIST] Re: Board-to-board connectors without reference planes?
- From: "Brownell, Michael P" <michael.p.brownell@xxxxxxxxx>
- To: "dmarc-noreply@xxxxxxxxxxxxx" <dmarc-noreply@xxxxxxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Wed, 4 Jun 2014 20:32:07 +0000
there is a return path, it may or may not provide adequate impedance control ...
most card edge connectors are not designed specifically for impedance control,
or they have wide impedance tolerances ...
the time a signal spends in a card edge connector is short relative to the
transfer rates shown in the QSeven spec, max freq ~ 3.75 GHz
and you've got an SMT connector, likely associated with a small via-board
footprint ... with lower crosstalk than most press fit footprints
in connector-land, one person's "it works" can be someone else's "major
headache" ... sometimes you have to measure a connector to
understand whether it’s the connector or something else in the channel causing
the ache
if you want some insight on how to measure PCIe connectors, a method adaptable
to other connectors, look in the Tools section at this site
http://www.intel.com/content/www/us/en/io/pci-express/pci-express-architecture-devnet-resources.html
there's no IP in the design or method, morph the design as needed to your
connector ... double-check the TRL delay times
be happy ... regardless of whether it works or it’s a headache
regards,
Mike
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of ckrich_99@xxxxxxxxx
Sent: Wednesday, June 04, 2014 12:41 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Board-to-board connectors without reference planes?
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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