John,
Using a probe head will not yield accurate results at high frequencies (>5GHz)
because the launch into the board will have a strong impact that can't be
deembedded.
Single ended and differential trace set-up can make a big difference depending
on stackup, material, Glass types, coupling... Tightly coupled
differentialtraces combined with resin-rich material will most likely let you
capture the dk and df data of the Resin, and ignore much of the Glass
influence. If you need just the dk and df of this special usecase, then that’s
ok, but be aware that this data might not be useful if the stackup changes.
Also be aware that you should never use microstrip because then your dk and df
values will be a result of a Mix of Air and Material.
The easiest way to extract dk and df is to measure the phase of two single
ended stripline traces with different length. This will yield very accurate
results for very high speeds and is really independent of copper roughness.
There was a DesignCon Tutorial 2016 by Terraspeed-Samtec, Isola and Simberian
about this topic: "A Material World, Modeling dielectrics and conductors for
interconnects operating at 10-50Gpps"
Best Regards
Gert
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-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On ;
Behalf Of John Lin
Sent: Tuesday, May 23, 2017 5:53 AM
To: si-list <si-list@xxxxxxxxxxxxx>
Subject: [SI-LIST] Differential vs. SE for PCB Dk/Df extraction
Hi SI gurus,
While using VNA to measurement traces on PCB for loss and Dk/Df extraction,
my colleagues say the differential handhold probe head can have wider bandwidth
than single ended handhold probe head. Is it true?
Can someone help to explain the reasons?
Also, for Dk/Df extraction, which is better structure, using single ended or
differential traces? Why?
Thank you for helps in advance.
Thanks,
John Lin
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