[SI-LIST] Re: Traces don't cause EMI - really?
- From: "Nagel, Michael" <Michael.Nagel@xxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 21 Oct 2003 15:43:28 +0200
For better reading:
http://tinyurl.com/rqip
Best regards,
Michael
> -----Original Message-----
> From: Nagel, Michael [mailto:Michael.Nagel@xxxxxxx]
> Sent: Dienstag, 21. Oktober 2003 13:15
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Traces don't cause EMI - really?
>
>
> Hello All!
>
> Reading the different contributions to this thread I hat to think back
> to my studies. Our Professor lecturing High Frequency Design talked of
> Microstrip Antennas.
>
> After a short search on google I found the below article
> (sorry for clipping
>
> the URL):
> http://www.navicpmart.com/advice/advicetmp.cfm/s/C7A13B2C9F173
> CF2E034080020B
> 4BBE117272197/v/001~~%2E%2E%2Fnews%2Fmw%5F200103%5F1%2Ecfm~~~~
> ~~~~~~~~.html
>
> The article describes well the principle of radiation of this type of
> antenna.
>
> I think that the frequency range is an important.
>
> This could help to sort out at which frequency which part of
> a PWB will
> possibly act as source.
>
> Best regards,
> Michael
>
>
> > -----Original Message-----
> > From: Chris Cheng [mailto:chris.cheng@xxxxxxxxxxxx]
> > Sent: Dienstag, 21. Oktober 2003 02:58
> > To: 'bdewitt@xxxxxxxxxxxxx'; leeritchey@xxxxxxxxxxxxx;
> > si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] Re: Traces don't cause EMI - really?
> >
> >
> > Brent & Lee,
> >
> > Nice spin on the issue but unfortunately you both tried to avoid the
> > original problem that Lee stated :
> >
> > >As far as EMI is concerned, it has been demonstrated many
> > times, once in
> > >the paper done by Doug Brooks with the staff at UMR, that
> > traces traveling
> > >over planes are not a detectable source of EMI. Therefore,
> > constraining
> > >the routing of differential pairs to prevent them from
> > creating EMI is not
> > >appropriate or necessary.
> >
> > I have seen and explained how surface trace can both fail EMI
> > and signal
> > integrity even if it is referencing to a solid plane and perfectly
> > terminated. If the edges are fast enough and the reference plane is
> > unrelated to the I/O power, the image current will be denied
> > a low impedance
> > return path and will exhibit strong EMI and power/ground
> > bounce. This is the
> > exactly reason why tight coupling differential traces can
> > help. This is also
> > the original claimed by proponents of coupled differential
> > signals and Lee
> > has chosen not to response to me. Whether the image current
> is flowing
> > between the differential traces or on the reference plane,
> > they cancel each
> > other out at both the driving and receiving end and thus
> > minimize both EMI
> > and power/ground bounce. Whether the reference plane is
> > related to the I/O
> > power or not does not affect the outcome in differential case
> > but make a big
> > difference in the single end signal case.
> >
> > To hide behind claims that since PC's or workstations have
> > surface trace
> > passing EMI and magically deduced that traces does not cause
> > EMI problem
> > makes as much sense as driving in the highway seeing no cops
> > pulling people
> > over for speeding and extending that to no one is speeding in
> > the highway.
> > Let me ask you this way, have you seen a highspeed system
> > that has surface
> > trace referencing to the wrong voltage plane pass EMI with an
> > open enclosure
> > without those crazy highspeed decoupling caps or thin core
> > planes to return
> > the image current ? I have seen plenty of them fail that way.
> > And yet I have
> > seen plenty of coupled differential signals route that way
> > and pass EMI or
> > signal quality. This is the fundamental advantage of coupled
> > differential
> > signals that you are so ignorant about.
> >
> > Lee,
> >
> > You seem to like to make claims that I can easily counter but
> > when face with
> > the rebuff you like to ignore it and continue to repeat your
> > flawed claim as
> > if no one can give you a counter example.
> >
> > In this forum, you have been asked many times the following
> question :
> >
> > "If tomorrow you are going into a client's office to consult
> > on designing a
> > 2.4GB/s differential signal system. Will you recommend them
> to "routed
> > thousands of differential signal where each member of the
> pair is on a
> > different layer". Do you think that is good engineering
> > practice ? Do you
> > think you can still keep your job as a consultant after making that
> > statement ?"
> >
> > And you seem to ignore the fact that this is how all these
> > differential
> > traces vs. single un-coupled lines discussion starts.
> >
> > This is a simple yes or no question. I don't even want to
> throw in any
> > technical point or science into it. You either do it or
> > don't. If you do, I
> > would propose you put that in your lecture notes and whatever
> > book you are
> > writing and call it "Lee Ritchey technique" or may be even
> > patent it as I
> > sure haven't seem anyone designing >GHz signals doing that.
> > As an inventor
> > of that technique, you deserve to publize it and make sure
> > people follow it.
> >
> >
> > On the other hand, you silence suggests you may have
> > something to hide in
> > you claim. It is plain wrong and even you yourself won't dare
> > to do that.
> >
> > Which way is it ?
> >
> > -----Original Message-----
> > From: Brent DeWitt [mailto:bdewitt@xxxxxxxxxxxxx]
> > Sent: Sunday, October 19, 2003 8:28 PM
> > To: leeritchey@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] Re: Traces don't cause EMI - really?
> >
> >
> > It seems this has become something of a tempest in a teacup.
> > As I mentioned
> > in an earlier post, I believe much of the energy of the dispute has
> > developed over differences in terminology.
> >
> > First, in the vast majority of cases, I agree with Mr
> Ritchey. In the
> > twenty five years or so I've been involved in EMC, I've
> never seen the
> > radiation from surface trace fail a product. That said,
> > I've only worked
> > on old/slow boards with fundamental clocks less than 1.5 GHz,
> > although I've
> > worked with 900 MHz intentional radiators to their 10th
> > harmonic. Rules of
> > thumb only work until the thumb is too fat to see the problem
> > underneath it.
> > As I mentioned in an earlier post, resonant patch antennas and other
> > intentional radiating pcb structures are nothing more than fat, well
> > designed traces. Somewhere between them and our ideal EMC
> > designs lies
> > practicality. As frequency increases, I find myself needing
> > increasingly
> > closer inspection of detail.
> >
> > In somewhat oblique support of Mr. Ritchey, most failing EMC
> > issues I've
> > observed have been associated with L di/dt induced voltages
> > on the reference
> > plane caused by surface traces. I/O cables, using said
> > poorly controlled
> > reference planes out to the world, are often a major
> > emissions issue, but
> > that is entirely another subject for discussion.
> >
> > Finally, I believe Mr. Ritchey is correct, but using the following
> > assumptions:
> >
> > - The trace structure and geometry does not approach a
> > resonant structure at
> > the fundamental or appreciable harmonics of the operating frequency.
> > - The reference plane structure supporting the return
> currents of the
> > surface trace does not significantly contribute to reference
> > plane resonance
> > and induced voltage on attached cables.
> >
> > Respectfully,
> >
> > Brent DeWitt
> >
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> >
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