[SI-LIST] Re: stupid VNA / TDR / TDT Measurement / Setup question

Hi Ege,
Can I get some clarification, please?  I'm probably misunderstanding =
something...

I'm not sure what you mean by the parallel plate mode propagating in =
this context.  Is it for the case where there is a voltage difference =
between the power and ground planes?  If that is so, wouldn't the =
dominant frequencies propagating in that mode have as their quarter =
wavelength the distance between the planes?  In the case cited, that =
would be 30mils, giving a full wavelength of 0.12 inches.  Assuming a Tp =
of 180ps/in, that gives a wavelength of 21.6ps, or a frequency of =
~46GHz, higher than we're usually concerned with in this context.  And, =
I'm not sure of the vehicle that's applying the voltage to the power =
plane - is it the capacitance between the trace and the plane?

Of course, I may have the physics (and corresponding math) completely =
wrong.  Please correct, as needed.

Also, if I understand you correctly, when you speak of the stripline =
mode, that's making the assumption that there is no voltage differential =
between the planes, hence a pure stripline configuration.

The actual condition will be a combination of the two modes.  The more I =
think of it, the more your representation makes sense, but I need some =
help with the specifics.

Thanks for your help,
Jeff Loyer



-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
On Behalf Of Ege Engin
Sent: Tuesday, November 18, 2003 1:34 AM
To: hermann.ruckerbauer@xxxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: 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) =
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!
>=20
> 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.....
>=20
> 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 ?
>=20
> thanks
>=20
> Hermann
>=20
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