[SI-LIST] 答复: [SI-LIST] Re: [SI-LIST] Re: 答复: [SI-LIST] Crosstalk and Overshoot/Undershoot
- From: "Shao, Peng" <Peng_Shao@xxxxxxxxxx>
- To: Newbie Pugal <pugal8686@xxxxxxxx>, Scott McMorrow <scott@xxxxxxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Fri, 1 Jul 2011 05:18:26 +0000
Pugal,
Basically, yes. The simulation tools can tell you the overall corsstalk and
reflections.
But by setting up the special and right environment, you may get the FEXT and
NEXT separately from simulation tools.
For the pure Xtalk, the duration of NEXT and the amplitude of FEXT is
proportion to the couple length.
But in practice, Xtalk always mixed with reflections. So, you need to do
different simulation by modifying the terminator scheme and trace length to
study each factors of Xtalk and reflections.
Shaopeng
AE Consultant Mentor Graphics Electronic Technology Co., Ltd.
Tel: +86-10 - 5930 4050
Cell: +86-136 1105 7707
Fax: +86-10-6808 0319
E-mail: peng_shao@xxxxxxxxxx
Address: RM1512, CanWay Building, No.66 NanLiShi Lu, Beijing, China 100045
-----邮件原件-----
发件人: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] 代表
Newbie Pugal
发送时间: 2011年7月1日 11:58
收件人: Scott McMorrow; si-list@xxxxxxxxxxxxx
主题: [SI-LIST] Re: [SI-LIST] Re: 答复: [SI-LIST] Crosstalk and Overshoot/Undershoot
Hi All,
Thanks for all the replies. Now one question on the tools and crosstalk
measurement. Does the simulation tools gives us the overall crosstalk values
due to FEXT and NEXT? Or else provides the values separately and which one to
worry most. I know that if there is a impedance mismatch at the near end NEXT
will reflect back to receiver on victim lines right, but how long the
generated crosstalk remains in its peak value?
What are all the boundary conditions need to be followed for crosstalk
simulations?
Thanks
Pugal
________________________________
From: Scott McMorrow <scott@xxxxxxxxxxxxx>
To: si-list@xxxxxxxxxxxxx
Sent: Thursday, 30 June 2011 7:53 PM
Subject: [SI-LIST] Re: 答复: [SI-LIST] Crosstalk and Overshoot/Undershoot
Shaopeng brings up a good point. However, I'd like to add a bit more
clarity
FEXT (Far End Crosstalk) and NEXT (Near End Crosstalk) are what we
measure in an interconnect system. They depend on both the coupling
coefficients of the interconnect, the directionality of the aggressor,
the topology of the interconnect, and any mismatches in the sections of
the lines, or the termination at all ends.
Forward Crosstalk and Reverse Crosstalk define the wave fronts that
propagate on perfectly matched uniform sections of the interconnect.
Forward crosstalk has the opposite polarity of the aggressor pulse.
Reverse Crosstalk has the same polarity of the aggressor pulse.
Measured FEXT may not be the opposite polarity of the aggressor pulse.
It is the instantaneous sum of all propagated Forward Crosstalk, and all
reflected Reverse Crosstalk on the interconnect from all possible
aggressors. If reflected Reverse Crosstalk is dominant, then measured
FEXT can have the same polarity as the aggressor pulse. Everything
depends on the interconnect system.
Scott
Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax
http://www.teraspeed.com
Teraspeed® is the registered service mark of
Teraspeed Consulting Group LLC
On 6/30/2011 10:05 AM, Shao, Peng wrote:
> Well, Pugal, one thing should be clear.
> Nobody says that " the values of far end crosstalk will be negative and near
> end cross talk will be positive."
> The polarity of FEXT and NEXT depends on what kind of signal switching on the
> aggressor.
>
> If there is a POSITIVE switching(rising edge) on aggressor, you will see "
> the values of far end crosstalk will be negative and near end cross talk will
> be positive."
> But if it is a falling edge on aggressor, things will be reversed.
>
> Shaopeng
> AE Consultant Mentor Graphics Electronic Technology Co., Ltd.
> Tel: +86-10 - 5930 4050
> Cell: +86-136 1105 7707
> Fax: +86-10-6808 0319
> E-mail: peng_shao@xxxxxxxxxx
> Address: RM1512, CanWay Building, No.66 NanLiShi Lu, Beijing, China 100045
>
>
> -----邮件原件-----
> 发件人: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] 代表
> Newbie Pugal
> 发送时间: 2011年6月30日 12:13
> 收件人: si-list@xxxxxxxxxxxxx
> 主题: [SI-LIST] Crosstalk and Overshoot/Undershoot
>
> Hi,
> The crosstalk theory says that the values of far end crosstalk will be
> negative and near end cross talk will be positive.
>
> If that is the case, does the negative far end crosstalk on the victim line
> leads to any undershoot problems? or it just reduces the noise margin levels
> in the victim lines?
>
> When to worry about overshoot and undershoot problems due to crosstalk?
>
> Thanks
> Pugal
>
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