[SI-LIST] Re: Differential Traces and GND planes
- From: <krishna@xxxxxxxxxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Fri, 16 Mar 2012 18:57:59 +0530
Hi everyone,
Thank you very much for your immediate help.
This question cropped up in my mind because am confronted with an issue in
my design, which involves one 3U VPX backplane connector having the
differential signals to be routed and terminated at another VPX backplane
connector on the same backplane board (for mating with another wafer which
can be inserted as and when required)
The GPIOs are the differential signals to be routed between these two
connectors. The total number of pins I have on the connector is just
sufficient for mapping all the signals I have on the Backplane connector. I
cannot afford for any GND signals, because I don't have pins. The
connectors I use are VPX 3U Backplane connectors.
In this scenario,
--Do I really need to keep every differential pair GPIOs sandwiched between
two ground pins?
--Since they are all GPIOs (very slow speed signals), is it OK to forget
about GND here?
Forget anyway that I would not be able to comply with VPX Backplane
recommended mapping table for this one particular connector. Please share
your wisdom to help me get things right.
Thanks a lot for all your answers. It's really helpful.
With Thanks and Best Regards,
Krishna.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of krishna@xxxxxxxxxxxxxxxxxxx
Sent: Friday, March 16, 2012 5:17 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Differential Traces and GND planes
Hi Everyone,
Differential traces perfectly cancel out the noise induced on the trace
provided the length of the two lines are same and are closely tied up all
along with the controlled impedance maintained throughout the routing.
But what is not sure is
1. Whether a solid ground plane is needed for a differential pair for
getting the full benefit of differential traces?
2. Are there any special considerations in making the choice - to
consider providing solid GND plane or get away with it - for say, better
EMI/EMC and crosstalk performance?
3. Is there any trade off involved?
Would you please help me get things right here if my understanding is wrong?
Thank you very much,
With Thanks and Best Regards,
Krishna.
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