[SI-LIST] Re: Crosstalk between the positive end and negative end of diffe
- From: wolfgang.maichen@xxxxxxxxxxxx
- To: "Eric Bogatin" <eric@xxxxxxxxxxxxxxx>
- Date: Tue, 12 Apr 2011 10:24:36 -0700
Icer,
if you don't have one of the commercial field solvers available you can do
this calculation with the free TNT/MMTL field solver. Just google "TNT
field solver", download is from Sourceforge.com or from my website
(http://www.testtechniques.com --> Free Tools). It will give you
propagation speed and line parameters, but also calculate near- and far-end
crosstalk directly for given coupled line length and rise time. Note that
the crosstalk calculations assume a linear ramp edge (like the basic Spice
edge model), and FEXT does not saturate in this calculator (in reality it
cannot exceed 50%). Also be careful about the units - default is meters,
not mils.
Wolfgang
From: "Eric Bogatin" <eric@xxxxxxxxxxxxxxx>
To: <si-list@xxxxxxxxxxxxx>
Cc: <eric@xxxxxxxxxxxxxxx>
Date: 04/12/2011 03:29 AM
Subject: [SI-LIST] Crosstalk between the positive end and negative end
of diffe
Sent by: si-list-bounce@xxxxxxxxxxxxx
Icer-
The far end noise in microstrip depends on the difference in speed between
the inverse of the odd and even modes. Not sure where you get the 200 mV-
depends on the odd and even mode speeds. If the two lines are far apart,
the
difference can be near zero.
You need to use a 2D field solver to calc the even and odd mode speeds
before you can estimate the far end noise.
This example in my book was offered to illustrate the real root cause of
far
end noise and why it scales with Len and inversely with rise time. If you
want to estimate the far end noise, any good 2D field solver, like the
Polar
SI9000 tool, will give this to you.
When the lines are close together and RT = 0.1 ( rather short for DDR2),
you
can indeed see far end cross talk of 10% in lengths on the order of 4-10
inches, depending on the coupling.
I would recommend you attend my Essential Principles of SI class in mid May
in Santa Clara. You will learn the real secrets of far end cross talk and
ground bounce, among other topics.
--eric
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Msg: #1 in digest
Date: Mon, 11 Apr 2011 02:50:45 -0700 (PDT)
From: icer world <icermail@xxxxxxxxx>
Subject: [SI-LIST] Crosstalk between the positive end and negative end of
diffe
Hi Experts:
In Eric's book, the crosstalk between the positive end & negative end
of the differential pair is discussed. I have a question about it.
The FEXT nosie is due to the different speed of odd & even and the
formula is V*(L/RT)*0.5*(1/Vodd-1/Veven). Take DDR for example, the L is
2in
and the RT=0.1ns and V is 1.8v, the noise will be 200mv and it's too much.
This means the single end of the differential pair always has much noise in
high speed design. However, this is a strange conclusion, so can someone
tell me whether it's right or not?
Thanks in advance.
Thanks
Icer
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