I have another question to EMI experts on the same lines and add few more
points in the discussion..
Which is good from EMI point of view.. stripline or microstrip routing?
I conducted few EMI simulation experiments long time back and found
something interesting.
experiment was related with microstrip vs stripline radiation using 3D EM
tool in real PCB condition and measured far-field@3m .
I found stripline radiation much higher than microstrip. This is
definitely not consistent with established myths..Normally stripline is
supposed to be better than microstrip routing for EMI. But, any stripline
routing in real PCB will come with at least 2 via transition to make
connection with components.
The conclusion was pointing towards that any via-addition in the layout
will create good amount of radiation. Therefore, stripline radiation was
worse than microstrip.
I am not sure how does this conclusion will apply to GND via stitching
fencing and ongoing discussion. But, any via addition in the layout does
not seem to be free insurance.
Another simulation experiment was related with radiation through bends
(90degree, 45 degree,45 degree mitred). I could not find any difference in
radiation till 10GHz. difference was marginal beyond 10Ghz. So 90 degree
bend radiation is also a myth. Many earlier discussion on si-list also
confirms the same conclusion.
it is not possible to simulate the absolute EMI radiation from given PCB.
But relative EMI assessment for different layout condition is definitely
possible.
Thanks
Sanjeev
SigIntegrity Solutions
www.sigintegrity-solutions.com
On Wed, Jul 6, 2016 at 8:54 AM, Istvan Novak <istvan.novak@xxxxxxxxxxx>
wrote:
Vow! What a flurry of messages!
Yes, there is no simple conclusion in this case. EMC is the most
complex among SI, PI and EMI,
having a lot of variables, making it useless to strive for simple,
generic conclusions to cover
all situations. The basic rules are the same, but conclusions can
strongly depend on the
specifics of the application. Most of the trouble comes from structural
resonances,
whether it is SI, PI or EMI. One simple differentiator: if the signals
dont excite the
resonances, they dont cause problems. So the same structure may or may not
cause problems and need fixes depending on what are the signals on them.
Second
differentiator is if for an 'unrelated' reason we already suppressed the
structural
resonances or the PCB is in a well-shielded box where I/O connections
have low
enough common-mode signal, there will be no need for other measures to
reduce
edge leakage.
I would not worry about half-wave resonances between adjacent planes in
the stackup:
if it is a signal cavity (plane-signal-plane), we can not come close to
the half-wavelength
plane-to-plane resonance as long as we want to maintain quasi-TEM
signaling. If it is
plane-to-plane cavity with no vertical via through the cavity to excite
it, it wont be a problem.
If it is a plane-to-plane cavity with vertical vias exciting the cavity,
the vias will similarly
resonate at half wavelength and unless it is intentionally done for some
specific reason, will
cause functional failures, so the edge radiation is irrelevant.
My approach to edge stitching comes from the other extreme argument:
unless someone
shows that it makes the radiation problem worse, AND as long as it can
be implemented
without increasing cost or blocking some necessary functions, this is an
insurance policy.
The stitching vias may not decrease radiation in the particular case, or
we may not need
the stitching because we may not excite the structural resonances, or
the box shielding
takes care of it, but if it is 'free' in every aspect and it can not
hurt, I dont see a reason
why we should not use it, at least in those cases where going after all
of the details to
get a black-and-white answer would take a lot of time and resources.
Regards,
Istvan Novak
Oracle
On 7/5/2016 10:17 PM, Doug Smith wrote:
Not a simple rule for design, just one to alert me when speeds get fastwrote:
enough I have to pay more attention. As you should know, I am not one
for simple rules. As a famous person at Bell Labs said "Rules are no
substitute for intellegence." I would have to say that for simulations
too.
Doug
On Tue, 5 Jul 2016 16:40:36 -0700, Lee Ritchey
<leeritchey@xxxxxxxxxxxxx> wrote:
AH! The quest for simple rules!
-----Original Message-----
From:si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Doug Smith
Sent: Tuesday, July 5, 2016 2:37 PM
To:si-list@xxxxxxxxxxxxx; Jeff Loyer<jeff.loyer@xxxxxxxxxx>
Subject: [SI-LIST] Re: Via fence along board edge
Hi Jeff,
Thanks, yes that is different. Seems like the far field radiation is
what is important here. Just looking for a simple rule that will
trigger when our designs get near a danger zone for edge radiation.
Doug
On Tue, 5 Jul 2016 14:26:56 -0700, Jeff Loyer<jeff.loyer@xxxxxxxxxx>
CharlesHi Doug,
You might note that Franz uses a near-field probe which will be >sensitive to a different phenomenon than what you're referring to.
Jeff Loyer[mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Doug Smith
-----Original Message-----
From:si-list-bounce@xxxxxxxxxxxxx >
Sent: Tuesday, July 5, 2016 2:22 PM
To:curtmcn@xxxxxxxxx;si-list@xxxxxxxxxxxxx; LeeRitchey; Grasso, >
fieldSubject: [SI-LIST] Re: Via fence along board edgefrequency. > Thanks. >
Hi Chas,
That seems to indicate problems well under the waveguide cutoff
DougLee > > Ritchey
On Tue, 5 Jul 2016 21:17:58 +0000, "Grasso, Charles"
<Charles.Grasso@xxxxxxxxxxxx> wrote:
Hah - at last! Simple language for the "restofus". :-)
Doug - Franz Gisins paper shows resonances well below 500GHz!!
Best Regards
Charles Grasso
Compliance Engineer
Echostar Communications
(w) 303-706-5467
(c) 303-204-2974
(t)3032042974@xxxxxxxxx
(e)charles.grasso@xxxxxxxxxxxx
(e2)chasgrasso@xxxxxxxxx
-----Original Message-----
From: Doug Smith [mailto:doug@xxxxxxxxxx] Sent: Tuesday, July 05,
2016 3:07 PM
To: Grasso, Charles;curtmcn@xxxxxxxxx;si-list@xxxxxxxxxxxxx;
want > > to show that an open side of a PCB is much like an open waveSubject: RE: [SI-LIST] Re: Via fence along board edge
Hi Lee,
It does not matter if the problem is made up. In this case, I
guide, > > but the the dimensions are so small that the interesting
frequencies > > are high enough as not to be a problem. This puts the
argument about > > PCBs into very simple language and that satisfies
engineering curiosity.
overall > > principle, which is what I am getting at.Citing lots of data does not lead to an understanding of the
assumptions on the dimensions, I get frequencies over 500 GHz where >So, I think the two cases are the same and was looking for your >insight. I have done the calculations, and making reasonable > >
edge radiation as from a waveguide would happen! Just wondering ifI > > did this correctly. Doug
<leeritchey@xxxxxxxxxxxxx> wrote:On Tue, 5 Jul 2016 13:56:08 -0700, Lee Ritchey > >
imaginary > > problem. >This seems to me to be another case of trying to solve an
problem > > actually > exists before I attempt to solve it.As a side comment on my posts and the responses to them, I oftensay > that I am from Missouri, and need to be shown that a
EMI > > from > energy leaking out the edges and none of them have hadIn almost 50 years of engineering and participating in the designof > more than 3000 PCBs, I have not yet seen one of them fail
via > > fences or > recessing to the 20h rule. So if the problem
really > > exists, the person > making the claim owes an example of a
failure > > due to the absence of > via fences.
[mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Doug SmithThere is a challenge for you! -----Original Message-----
From:si-list-bounce@xxxxxxxxxxxxx > > >
on > > > > EMISent: Tuesday, July 5, 2016 1:32 PMsi-list@xxxxxxxxxxxxx; Lee Ritchey<leeritchey@xxxxxxxxxxxxx>
To:Charles.Grasso@xxxxxxxxxxxx;curtmcn@xxxxxxxxx; >
Subject: [SI-LIST] Re: Via fence along board edgewavelength > (at some very high
Lee, a question. If the spacing between two planes was 1/2
frequency) would not the edge of the board be a little like anfew > years. Doug
open waveguide? Probably not a practical case, at least not for
another
On Tue, 5 Jul 2016 11:39:53 -0700, Lee Ritchey ><leeritchey@xxxxxxxxxxxxx> wrote:
I think I have traced this myth to its origin. It is no more orless > than a
does > > not "leak out" the sides of a PCB to begin with. One ofmyth. >
The following papers all show with laboratory testing that EMI
them even >
shows that with or without these "grounding vias" the results arethe > same. > > > >
on > > Electromagnetic Radiation From Printed Circuit Boards", UCBrooks, Douglas. "90 Degree Corners, The Final Turn." PrintedCircuit > Design. January 1998
Fang, Jiayuan, et.al., "Effects of 20-H Rule and Shielding Vias
Santa
Cruz, > Publishing date unknown. > >
Chen, Huabo, et.al., "Effects of 20H Rule and Shielding Vias
if > > > > there will be an interference problem or not then a viain > PCBs", UC Santa Cruz EE Department, May 2001. > >
Hope this helps. >[mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Grasso, Charles
Lee Ritchey
-----Original Message-----
From:si-list-bounce@xxxxxxxxxxxxx >
Sent: Tuesday, July 5, 2016 9:21 AMdon't have a simulation tool or handy dandy formula to "guess"
To:curtmcn@xxxxxxxxx;si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Via fence along board edge
If there is a concern about cavity resonances causing EMI and
you
fence is > > > a
Subject > > > > >outsidegood way to sleep at night! (Just count vias instead of sheep >..one..two...three...zzzzzzz)
Best Regards[mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Curt McNamara
Charles Grasso
Compliance Engineer
Echostar Communications
(w) 303-706-5467
(c) 303-204-2974
(t)3032042974@xxxxxxxxx
(e)charles.grasso@xxxxxxxxxxxx
(e2)chasgrasso@xxxxxxxxx
-----Original Message-----
From:si-list-bounce@xxxxxxxxxxxxx >
Sent: Tuesday, July 05, 2016 6:51 AMwaves
To:si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Via fence along board edge
I have seen this done, and understand the desire to trap EM >
inside the PCB. > > There are parts and short traces on the > >
layers, with ground
pours. > The next layer in is ground on both top and bottom. >
Will the ground fence always help with EMC?will > come out any opening it can find?
- Or sometimes help because that energy has to go somewhere and
- Or mostly help because those openings are small compared towavelength?
the
Curt
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