[SI-LIST] Re: WG: stupid VNA / TDR / TDT Measurement / Setup question
- From: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
- To: <hermann.ruckerbauer@xxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Wed, 19 Nov 2003 09:51:05 -0800
VNA and TDR should correlate, with appropriate conditions set on =
bandwidth vs. risetime.
Can you provide a few more details?
Which S parameters looked strange, and how?
What frequency VNA? What risetime TDR?
When you measure Sig3 & 4, are you using the ground or power plane as =
your reference (TDR & VNA)?
Have you done a TDT?
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
On Behalf Of hermann.ruckerbauer@xxxxxxxxxxxx
Sent: Wednesday, November 19, 2003 2:03 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] WG: stupid VNA / TDR / TDT Measurement / Setup =
question
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
-----Urspr=FCngliche Nachricht-----
Von: Ege Engin [mailto:engin@xxxxxxxxxx]=20
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.=20
Hope this helps.
Ege Engin
hermann.ruckerbauer@xxxxxxxxxxxx schrieb:
>=20
> Hello all,
>=20
> I do have a stupid question, maybe you can enlighten me ....
>=20
> Assuming a 6 layer board (Sig1 / GND / Sig2 / / Sig3 / Power / Sig4)=20
> with some single ended ustrip and stripline transmissionlines=20
> 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=20
> teststructures does have a signal pad and a GND pad for contacting=20
> with the probe. Therefor I'm fine with Sig1 and Sig2! both are nice=20
> GND referenced, therefore I do not expect a problem with the=20
> measurements there!
>=20
> But Signal 3 and 4 are Power referenced. And so far there is not too=20
> much AC short between PWR and GND plane. The distance between this=20
> planes is > 30 mil, therefore I would expect the most AC short coming=20
> from the Vias. And now I'm not really sure what happens, if I'm doing=20
> a VNA / TDR / TDT measurement on Sig3 and Sig4, which are Power=20
> referenced, as my measurement ground is connected to the GND plane on=20
> the board.....
>=20
> Can the results tell me something, or can I forget the results=20
> completly ??? Is there a difference for VNA / TDR or TDT Measurments=20
> in this case ?
>=20
> thanks
>=20
> Hermann
>=20
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