[SI-LIST] WG: stupid VNA / TDR / TDT Measurement / Setup question
- From: hermann.ruckerbauer@xxxxxxxxxxxx
- To: si-list@xxxxxxxxxxxxx
- Date: Wed, 19 Nov 2003 11:02:41 +0100
I got one more answer, and Ege asked me to forward this mail to the list. It
is the mail below ....
In the meantime i got some measurement results. For the TDR measurement it
looks, that the "missing" Referencing is not showing big effects. The
results for Sig3 and Sig4 looks reasonable and are in the same region than
the Sig1 and Sig2 results.
But the VNA S-parameter Measurments for Sig3 looks very strange, and Sig4 is
even worse. So far there are no passives on my board for providing any AC
coupling. And basically I do not want to spend to much of effort in this
measurements (Sig1 and Sig2 are enough for me), I would be just interested
in the difference between the VNA and the TDR measurement !
thanks
Hermann
-----Ursprüngliche Nachricht-----
Von: Ege Engin [mailto:engin@xxxxxxxxxx]
Gesendet: Dienstag, 18. November 2003 10:34
An: Ruckerbauer Hermann (MP PDT PD DES5)
Cc: si-list@xxxxxxxxxxxxx
Betreff: Re: [SI-LIST] stupid VNA / TDR / TDT Measurement / Setup question
Hello Hermann,
You can think of your stripline Sig3 as a multiconductor transmission line
(i.e., you have 3-conductors: power, ground, and signal). Two transmission
line modes can propagate here: parallel-plate and stripline modes. So if you
launch a signal on Sig3 while referencing the ground plane, you excite both
modes. Note that the power plane is not connected to anything, i.e. it is
floating. This can be used to reduce the stripline model, which can be
obtained considering the two modes, to a single transmission line model with
a slightly higher characteristic impedance than the stripline. In
conclusion, what I would expect to observe in measurement is still a
transmission line but with a higher characteristic impedance than expected.
I think, Jeff Loyer's experiments can also be interpreted in this way. We
have performed 4-port measurements on such stripline structures with a VNA,
and have clearly observed the coupling between ports referenced to the power
and ground planes and got a good correlation between measurement and
stripline model based on two modes.
Hope this helps.
Ege Engin
hermann.ruckerbauer@xxxxxxxxxxxx schrieb:
>
> Hello all,
>
> I do have a stupid question, maybe you can enlighten me ....
>
> Assuming a 6 layer board (Sig1 / GND / Sig2 / / Sig3 / Power / Sig4)
> with some single ended ustrip and stripline transmissionlines
> teststructures on all 4 signal layers. There are no passive components
> on the PCB (e. g. no C) My probes do have a signal and a GND pin. All
> teststructures does have a signal pad and a GND pad for contacting
> with the probe. Therefor I'm fine with Sig1 and Sig2! both are nice
> GND referenced, therefore I do not expect a problem with the
> measurements there!
>
> But Signal 3 and 4 are Power referenced. And so far there is not too
> much AC short between PWR and GND plane. The distance between this
> planes is > 30 mil, therefore I would expect the most AC short coming
> from the Vias. And now I'm not really sure what happens, if I'm doing
> a VNA / TDR / TDT measurement on Sig3 and Sig4, which are Power
> referenced, as my measurement ground is connected to the GND plane on
> the board.....
>
> Can the results tell me something, or can I forget the results
> completly ??? Is there a difference for VNA / TDR or TDT Measurments
> in this case ?
>
> thanks
>
> Hermann
>
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