Dear colleagues,
Recently I received a request to work out a method that, based on the
geometries of tline and the materials used, is able to calculate a unit loss
of tline. This is a new challenge for me since previously I used two ways to
obtain the loss of tline:
One is sim + measurement. With measured result adjusted simulation
parameters, we are able to give pretty accurate prediction on the future
constructions of boards built with same or similar geometries/materials.
Sim-only is the second option, which has to be adopted when lab measurement
is not available. The estimation accuracy of this method depends on how
reliable the data provided by vendors, mainly Df and roughness, and, our
luck😊
To speed up the design cycle, our customer now is asking if we can develop a
sim-free method of estimating the loss. It seems to me a doable task but
before I start planning the work, I'd like to learn a little more from those
who have gone before me. Specifically,
1. how accurate is a loss estimate based on computation? I believe that in
order to achieve a good enough accuracy (<10%), a number of factors have to
be taken into account including the frequency-dependency of Dk, Df;
roughness model; copper conductivity; and so on.
Given the wide range of the materials as well as the tline geometries, 10%
without doing DOE correlation appears a very difficult goal to achieve. Do
you agree?
2. To reduce the complexity, the influences of temperature and humidity
probably can be left out of the core formula, and be applied as an
additional %.
Thanks you for sharing your thoughts.
Regards,
Sherman Shan Chen
SI/PI Group, Kandou Bus
5 Queensbridge, Northampton, UK, NN4 7BF
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx <> On Behalf Of Havermann Gert
("Gert.Havermann")
Sent: Tuesday, April 12, 2022 7:31 AM
To: qantrix@xxxxxxxxx; Si-list <si-list@xxxxxxxxxxxxx>
Subject: [SI-LIST] AW: [EXTERNAL] SCD21 needs extac lenght to fix
Hi,
it seems to be a problem with "local skew". On diff pairs at higer speeds it
isn't enough to deskew at the ends of traces, you have to deskew at each
bend directly to keep mode conversion low.
BR
Gert
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-----Ursprüngliche Nachricht-----
Von: si-list-bounce@xxxxxxxxxxxxx <si-list-bounce@xxxxxxxxxxxxx> Im Auftrag
von qantrix
Gesendet: Mittwoch, 6. April 2022 16:15
An: Si-list <si-list@xxxxxxxxxxxxx>
Betreff: [EXTERNAL] [SI-LIST] SCD21 needs extac lenght to fix
Hello experts
working on interface where i see SCD21 violates the spec.
the layout tool shows zero prop.delay difference.
its stripline on thick dielectrics (10mil) and 10/10/10mil traces on
taychon 100G after divide trace to segments I see that there is only one
turn causing this skew.(extracting segment parts and check scd)
compensating this turn with extra bend and tweaking the same length for P
and N (measured manually in hfss) still shows bad scd21.
When I added extra length on the inner trace (in range of 15mil) I got
SCD21 down to -20dB.
thats is not sound physically right... looking to understand root cause
tried to draw those traces:: :)
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