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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