Thank you very much for your reply.
Besides, for Serdes, sometimes, the total link will go across several brds,
cables. Two lanes may go parallel close to each other on one brd, but not
be neighbours in the other brds. Then how could we judge their FEXT and
NEXT risks?
Regards
On Wed, Dec 23, 2015 at 11:27 PM, Richard Allred <richard.allred@xxxxxxxxx>
wrote:
FEXT xtalk is typically synchronous and thus has a fixed phase relation
while NEXT is asynchronous so it does not have fixed relative position.
This is quite clear if you apply peak distortion analysis to the link.
Richard Allred
On Wed, Dec 23, 2015 at 8:00 AM, jun zhang <zhangjun5960@xxxxxxxxx> wrote:
Hi Richard,
but Serdes lane has no requirement of length match and therefore FEXT can
also be in the same relative position in the victim eye, I think.
Regards
On Wed, Dec 23, 2015 at 11:13 AM, Richard Allred <
richard.allred@xxxxxxxxx> wrote:
I think the reason for the difference in the spacing is two fold. One,
NEXT
is usually stronger than FEXT since it isn't attenuated as much by the
channel and two, the xtalk phase relation.
For two DQ signals in the same byte group, they are always going the same
direction and their edge transitions have a somewhat fixed phase relation
to each other. The crosstalk will always be in the same relative position
in the victim eye.This is far end xtalk (FEXT).
For two signals that go opposite directions, the phase relation of the
edge
transitions are not fixed. This means that this near end crosstalk can
attack any position in the eye and so on average is worse than a fixed
phase relation.
If you allow me, I would say it is because:
FEXT is proportional to (Kc - Kl) while NEXT is proportional to Kc+Kl
where
Kc=Capacitive coupling coeficient and Kl=Inductive coupling coeficient.
Even more, NEXT prevails during all agressor signal travel so I understad
it is more sensitive than FEXT.
Lets see what more experienced people say.
Ivan Perino
On 22 dic 2015, at 22:25, Carson Au <carsona@xxxxxxxxxxxx> wrote:it
NEXT and FEXT.
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On 23 December 2015 at 12:17, jun zhang <zhangjun5960@xxxxxxxxx>
distance
I have a question about the spacing differences between TX to TX
whereand TX to RX distance. For example, in Intel PDG, TX to RX distance
requirement is stricter than TX to TX requirement. For example, for
SATA-Gen3, TX to TX: 7h for microstrip; TX to RX: 9h for microstrip
thinkh is the height of the mcrostrip layer.
If FEXT for TX to TX is -20db and NEXT for TX to RX is also -20db, I
------------------------------------------------------------------their noise levels are the same. Then why does Intel give stricter
requirements for the distance between TX to RX?
--
best wishes,
Jun Zhang
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best wishes,
Jun Zhang
