Hi Istvan,
What I was alluding to was the fact that "high speed routing" seemed not to
be a factor in EMI, else the transition to differential signaling would have
impacted the EMI signature of Intel systems. I never heard any mention of
that. On the other hand, Lee says that his experience was otherwise, so
single-ended signaling seems to contribute. I'm guessing at this point that
I only had visibility to well-designed systems where high speed routing was
carefully controlled, over continuous return paths, for instance. Lee might
have been exposed to less carefully designed systems and observed the
benefits of differential signaling. Interesting information, perhaps
explaining something that has bothered me for years (why we, Intel, didn't
see an improvement in EMI when we went to differential signaling).
Thanks all for sharing your insights - always nice to learn more.
Jeff Loyer
-----Original Message-----
From: Istvan Novak [mailto:istvan.novak@xxxxxxxxxxx]
Sent: Wednesday, July 6, 2016 8:12 PM
To: jeff.loyer@xxxxxxxxxx; Sanjeev Gupta
Cc: si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Re: Via fence along board edge, stripline vs.
microstrip
Jeff,
I am not sure I follow the logic: in case there was no EMI problem with the
single-ended front-side bus, if you make it better by turning it to
differential, it still wont have EMI problem.
So from the perspective of complaints, there is no change (zero before, zero
after). Or are you saying that there were EMI issues with the single-ende
front-side bus and with the differential front-side bus the EMI problems
remained unchanged?
Regards,
Istvan Novak
Oracle
On 7/6/2016 11:18 AM, Jeff Loyer wrote:
Something that I’ve wondered about is: If microstrip (or stripline)------------------------------------------------------------------
might cause EMI, how come Intel never saw any significant difference
when they went to differential busses between processors? Intel
replaced the single-ended front-side bus (high EMI) with differential
signaling (low
EMI) for communication between the processors and memory controller
and yet I’ve never heard anyone write (or remark) that this made an
impact on the EMI signature of their servers or desktops.
*Jeff Loyer*
*From:* Sanjeev Gupta [mailto:sanjeev@xxxxxxxxxxxxxxxxxxxxxxxxxx]
*Sent:* Wednesday, July 6, 2016 6:06 AM
*To:* istvan.novak@xxxxxxxxxxx
*Cc:* doug@xxxxxxxxxx; si-list@xxxxxxxxxxxxx; Jeff Loyer; Lee Ritchey
*Subject:* Re: [SI-LIST] Re: Via fence along board edge
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
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