[SI-LIST] Re: Estimating Crosstalk
- From: <Wolfgang.Maichen@xxxxxxxxxxxx>
- To: <istvan.novak@xxxxxxxxxxx>, <markfilipov81@xxxxxxxxx>
- Date: Wed, 7 Dec 2011 13:56:45 +0000
Well, Istvan's last paragraph puts what I was trying to say into more concise
terms. My formula is the approximation for differential-to-differential
crosstalk, i.e. a differential signal on the aggressor pair inducing a
differential signal on the victim pair.
Wolfgang
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Istvan Novak
Sent: Wednesday, December 07, 2011 2:50 PM
To: markfilipov81@xxxxxxxxx
Cc: SI LIST
Subject: [SI-LIST] Re: Estimating Crosstalk
Mark,
The xtalk ~ 1/(1+(d/h)^2)) formula gives you the the estimated near-end
inherent crosstalk in microstrip in the saturated case. This assumes
matched terminations on the connections. In striplines the decay of
crosstalk
(near-end, saturated) rolls off with the fourth power of distance, which
can be approximated with exponential in a certain range if you wish. In
perfectly homogeneous striplines there is no inherent far-end crosstalk
in matched case. When the connections are mismatched, the total crosstalk
noise goes up in both microstrip and stripline due to the reflections.
In the frequency domain the crosstalk response varies sinusoidally
with frequency and if you transform the time-domain crosstalk waveform
properly into the frequency domain, you get this response, and vice versa.
As a first approximation, for crosstalk, differential traces can be
looked at
as two single-ended traces, and relying on the linearity of the coupled
structure, you can work out the result as a superposition of single-ended
responses. You will have four permutations though creating the
interaction among common-mode and differential-mode excitations and
responses.
Regards,
Istvan Novak
Oracle
Mark Filipov wrote:
> Thank you all, for your valuable comments and advices!
> So, to conclude about this formula, xtalk ~ 1/(1+(d/h)^2)). This gives
> fairly accurate (electric) field distribution of the surface
(single-ended)
> microstrip traces, from trace to trace. It also gives the worst case
> scenario for the crosstalk.
> However which xtalk does it give? Total xtalk? Since for microstrips, the
> FEXT increases with the lenght of traces. For striplines traces
> the xtalk (NEXT?) decreases exponentially when we increase the spacing,
> i.e. xtalk ~ e^(-d).
> To see how much xtalk is created on the victim line by the aggressors
> line, it depends on the frequency of the data stream and on the data
> pattern of the aggressor line. Higher the switching frequency, more
> crosstalk is to be expected, since it's proportional to the switching
speed
> (we know that for FEXT).
>
> How about the NEXT? How is NEXT dependent of the switching speed (rise
> time/fall time).
>
> Which data pattern should create most xtalk for digital circuits,
> 0101010.... or "1" in a long pattern of "0" or something else?
>
> How well does this equation hold when we have differential pair traces
> (surface microstrips)? Or is there any other equations for predicting
> worstcase xtalk for diff pairs traces?
>
> Best regards,
> Mark
>
>
> 2011/12/6 <Vittal.Balasubramanian@xxxxxxx>
>
>> Keep in mind that any empirical equation gets less and less accurate as
>> your frequency of interest goes higher and higher. So make sure you know
>> what your frequencies of interest are and the range of accuracy of any
>> equations.
>>
>> Best regards,
>> Vittal Balasubramanian
>> Staff Signal Integrity Engineer
>> FCI USA LLC
>> (717) 938-7368
>> -----Original Message-----
>> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>> On Behalf Of Wolfgang.Maichen@xxxxxxxxxxxx
>> Sent: Tuesday, December 06, 2011 2:49 AM
>> To: dbrooks9@xxxxxxxxxxxxxxx; markfilipov81@xxxxxxxxx;
>> si-list@xxxxxxxxxxxxx
>> Subject: [SI-LIST] Re: Estimating Crosstalk
>>
>> Yes, this is what I saw when experimenting with a 2D solver. Microstrip
>> follows this behavior. The problem is using this for stripline - the
>> trend is VERY different - whereas Microstrip has a 1/d^2 behavior for
>> large spacings (see formula), striplines follow an exponential (e^-d)
>> behavior, which drops of very fast - much faster than 1/d^2 - for larger
>> line-to-line spacings.
>>
>> Wolfgang
>>
>>
>>
>> -----Original Message-----
>> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>> On Behalf Of Doug Brooks
>> Sent: Monday, December 05, 2011 6:25 PM
>> To: Mark Filipov; si-list@xxxxxxxxxxxxx
>> Subject: [SI-LIST] Re: Estimating Crosstalk
>>
>> In studies I have done (see especially
>> <http://www.ultracad.com/mentor/crosstalk_coupling.pdf>Crosstalk
>> Coupling: Single-ended vs. Differential on our website,
>> www.ultracad.com) This formula (1/(1+(d/h)^2)) works pretty well
>> for Microstrip. It is a worst-case formula for stripline, depending
>> on conditions. This is shown with Hyperlynx simulations in the article.
>> There is a freeware calculator, also on our website, that is based on
>> this formula (taken from Howard Johnson's first book and an interview
>> with him.)
>>
>> Doug Brooks
>>
>>
>>
>>
>> At 07:39 AM 12/5/2011, Mark Filipov wrote:
>>> In many books dealing with SI & PCB's, (Brooks, Johnson&Graham,
>> Khandpur,
>>> ..) there is a simple equation for estimating crosstalk.
>>>
>>>
>>> Crosstalk between two traces separated by distance D, and which both
>> are at
>>> distance, H, from their reference plane is proportional to
>>>
>>>
>>>
>>> K / (1 + (D/H)^2 ), where K < 1. Usually, I have seen that K is set
>> equal
>>> to 1.
>>>
>>>
>>> In book "Grounds for Grounding" recently published by IEEE Press (Joffe
>> &
>>> Sang Lock), on page 835 (which can be seen online in Google Books),
>> there
>>> is stated "... Assuming a trace width of 10 mils placed above the
>> return
>>> plane with separation, h, of 10 mils, the crosstalk between the traces
>>> (where the traces are separated by 40 mils) will have an upper bound of
>>> 1/(1+(d/h)^2) = 1/(1+4^2) = 0.06 = -25 dB "...
>>>
>>> How well does this equation agree with empirical data? Is it an upper
>> bound
>>> for estimating crosstalk?
>>> Does this equation give only the amount of coupling between the traces,
>>> since crosstalk is also data pattern dependent?
>>> How does this equation relate for estimating crosstalk between
>> differential
>>> pair traces, separated by distance D?
>>>
>>> I have seen an similar expression K/(1+(D/H)^2)), when estimating how
>> far
>>> the return current will spread underneath the traces, so I guess this
>>> formula is derived on basis of that??
>>>
>>> BR /Mark
------------------------------------------------------------------
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 technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
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 technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
