[SI-LIST] Re: Q on Trace Width and Jitter for Diff Pairs
- From: "Leonard Dieguez" <leonard.dieguez@xxxxxxxxxx>
- To: <rsefton@xxxxxxxxxxxxx>, <Charles.Grasso@xxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Wed, 6 Jul 2005 07:19:37 -0700
Robert,
DJ, has a few different components. There is jitter that is correlated
to the data and jitter that is not correlated. An example of
uncorrelated jitter would be switching power supply noise that would
make it way into the transmitter or the data stream somehow. Correlated
jitter also comes in a few forms as well. Jitter cause by impedance
discontinuities fall into Data dependant jitter. In most normal
applications of High speed signaling this type of jitter is hard to
counteract. I will normally stress this to customers and put a lot of
attention into designing vias, BGA breakouts, connector breakouts,
surface mount component selection and layout and other PCB structures.=20
Another form of DJ that we all commonly see at multi gigabit speeds is
Inter-symbol Interference. This is caused by the frequency dependencies
of the transmission channel. FR4 is one of the worst offenders. In
simplistic terms you can think of your FR4 PCB as a low pass filter. The
higher frequency components are attenuated and the lower frequencies are
passed. One thing that happens is that the bit energy will get smeared
over time so you have the situation where a nice crisp rising or falling
edge is input to the channel and at the output of the channel the
falling edge will cover several bit times. Since our goal is to have our
edge to occur within one bit time we have techniques to counter some of
the effects of ISI, mainly transmit equalization (pre emphasis) and
receive equalization (continuous time and DFE).=20
Leonard Dieguez
System IO Specialist.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Robert Sefton
Sent: Tuesday, July 05, 2005 3:23 PM
To: Charles.Grasso@xxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Q on Trace Width and Jitter for Diff Pairs
Hi Charles -
Nobody has really addressed the jitter question. It doesn't seem to me
that
jitter is directly related to signal loss, regardless of whether the
loss
comes from skin effect or the dielectric. But DJ is directly affected by
reflections caused by impedance variations, correct? Widening traces
decreases the impedance variation caused by imperfect etching, which
could
decrease DJ. That's my best guess anyway.
Regards,
Bob Sefton
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On
Behalf Of Grasso, Charles
Sent: Tuesday, July 05, 2005 11:39 AM
To: 'si-list@xxxxxxxxxxxxx'
Subject: [SI-LIST] Q on Trace Width and Jitter for Diff Pairs
Greetings!
=20
I am stuck on understanding a contradiction - perhaps someone could
"unstick" me?
It is understood that (at high frequencies) the dielectric losses in a
pwb
dominates the losses of a transmission line. However, I have read in
various
publications that increasing the trace widths improves the jitter
performance of a high speed serial link.
I would have thought that as a trace width increases the effects of the
dielectrics would be exacerbated.
=20
How does increasing the width of a trace improve the DJ of the link?
=20
Best Regards
Charles Grasso
Senior Compliance Engineer
Echostar Communications Corp.
Tel: 303-706-5467
Fax: 303-799-6222
Cell: 303-204-2974
Pager/Short Message: 3032042974@xxxxxxxx <mailto:3032042974@xxxxxxxx>
Email: charles.grasso@xxxxxxxxxxxx; <mailto:charles.grasso@xxxxxxxxxxxx;
>
Email Alternate: chasgrasso@xxxxxxxx <mailto:chasgrasso@xxxxxxxx>=20
=20
=20
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List FAQ wiki page is located at:
http://si-list.org/wiki/wiki.pl?Si-List_FAQ
List technical documents are available at:
http://www.si-list.org
List archives are viewable at: =20
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List FAQ wiki page is located at:
http://si-list.org/wiki/wiki.pl?Si-List_FAQ
List technical documents are available at:
http://www.si-list.org
List archives are viewable at: =20
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
=20
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List FAQ wiki page is located at:
http://si-list.org/wiki/wiki.pl?Si-List_FAQ
List technical documents are available at:
http://www.si-list.org
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
