[SI-LIST] Re: Routing of synchronous bus signals
- From: Hermann Ruckerbauer <Hermann.Ruckerbauer@xxxxxxxxxxxxx>
- To: thulasi.ramu@xxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Mon, 03 Feb 2014 09:15:21 +0100
Hello,
I don't linke the 2W rule, as it is not the width of the lines but the
spacing (dielectric height) to the referencing that defines the level of
crosstalk. Due to common used stackups this is often resulting in a
similar result if you are using 2x the width or 2x the dielectric hight.
Second thing I don't like in such discussions is, that they are missing
on wich layer is routed. it is a difference if the routing is done on
Top/Bottom as Microstrip or on inner layer as stripline.
Regarding the signals travelling in oppsosite direction: This brings in
the ascpect of FEXT vs Next. I try to limit my NEXT by adding some
additional space between the singal groups runnin in opposite
directions. Usually this is just a single additional spacing that I make
bigger (even on cost of the spacing of signals that run in the same
direction (if really required)).
And last but not least: not really the 105MHz are the relevant factor,
but the slewrates of the signals. If you have some new devices that
drive high slew rates even at this low frequency this might cause
trouble. In the last year I had several failure analysis projects, where
the change to a new DRAM (SDR or DDR1 speed range) caused the system to
fail. On the memory interface this means, that the interfaces was not
characterized good enough (e. g. just by a Pass/Fail test at different
temperatures), and now only a "slight" change makes the system fail.
So even if you have today a device with a slow slew rate .. if you need
to consider a different device later on consider that this might have
higher slew rates.
Hermann
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schrieb Thulasi Ramu J:
> Hi,
> I want to route 105MHz speed synchronous bus signals.
> Synchronous Bus contains data and control signals.
> Some signals are travelling in one directon and some are in the opposite
> direction.
>
> I am providing 2W spacing between the signals travelling in the same
> direction.
> Do I need to provide additional spacing for the signals travelling in
> opposite direction ?
>
> Or can i route all the signals by providing 2W spacing ?
>
> Regards,
> Thulasi
>
>
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