[SI-LIST] Re: Stripline vs. Parallel Plate Impedances
- From: Ege Engin <engin@xxxxxxxxxx>
- To: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>, si-list@xxxxxxxxxxxxx
- Date: Wed, 03 Dec 2003 17:12:05 +0100
Hello Jeff,
The reason I use the terms "stripline and parallel plate modes" is the
transmission line basis of the modeling approach (e.g., similar to the
even and modes of a balanced differential line.). But there is indeed a
confusion when I say these are the (TEM)-modes in a "stripline", since
stripline is commonly understood as the pure stripline configuration
(hence has only the stripline mode associated with it). Maybe calling
this structure a "3-conductor stripline" (plane1, signal, plane2) would
be more clear.
If one of the planes is floating and you reference only the other one
for measurement, the resulting characteristic impedance should be
slightly higher than the impedance seen when both planes are short
circuited. I don't have a good qualitative explanation for that (maybe
the inductance goes high due to current return path discontinuity at the
launchers?). I came to this conclusion simply by reducing the
"3-conductor stripline model" by floating one of the planes.
Best Regards,
Ege Engin
"Loyer, Jeff" schrieb:
>
> Hello Ege,
> Thanks for the clarification. If you don't mind, it brings up some more
> comments & questions in my mind, however.
>
> I think more appropriate terms might be stripline and parallel plate
> "configurations", rather than "modes".
>
> If you are assuming superposition of the two impedances (stripline and
> parallel plate), can you predict in a qualitative sense whether the resultant
> net impedance will be higher or lower than that of the 2 individual
> configurations? I would have "guessed" that the net impedance would be less
> than just that of the stripline configuration. But that's contrary to what
> you're finding. Any explanation of why the impedance goes up?
>
> Thanks again for your indulgence,
> Jeff Loyer
>
> -----Original Message-----
> From: Ege Engin [mailto:engin@xxxxxxxxxx]
> Sent: Thursday, November 27, 2003 3:19 AM
> To: Loyer, Jeff
> Cc: si-list@xxxxxxxxxxxxx; hermann.ruckerbauer@xxxxxxxxxxxx
> Subject: Re: [SI-LIST] Re: stupid VNA / TDR / TDT Measurement / Setup question
>
> Hi Jeff,
>
> The stripline mode that I was talking about is exactly what you
> mentioned. The parallel-plate mode that I was referring to is also a TEM
> mode, so I was not referring to the higher modes that can be excited
> above such cut-off frequencies as you calculated. Actually I assume that
> we are below these cut-off frequencies, such that we have only the TEM
> waves. (Losses can be taken into account later by using lossy
> transmission line models, but inhomogeneous media poses some
> difficulties, so it is assumed that the medium between the planes is
> homogeneous.)
>
> Strictly speaking the stripline and parallel-plate modes can be defined
> as:
>
> Stripline mode: No voltage differential exists between planes. This mode
> represents the signal transmission and corresponds to a conventional
> pure stripline configuration as you mentioned (e.g., both planes are
> connected with vias at the launchers).
>
> Parallel-plate mode: No current flows on the signal line. This mode
> represents the power distribution and can be modeled as a parallel-plate
> transmission line with the well-known characteristic impedance
> sqrt(mu/eps)*height/width. For wide planes a 2-dimensional plane model
> could be more appropriate.
>
> The actual voltages and currents can be obtained as a combination of the
> mode currents and voltages. The composition of the modes (i.e., how we
> combine them) can be defined by a transformation matrix, which can be
> obtained by forcing that it must diagonalize the inductance and
> capacitance matrices. You can find more information about these in a
> paper that I presented recently at EPEP'03:
>
> "Modeling of Non-Ideal Planes in Stripline Structures"
>
> Note that we get the stripline and parallel-plate modes only for a
> homogenous medium. If the medium between the planes is inhomogeneous, we
> don't have pure stripline and parallel-plate modes (i.e., they are
> coupled to each other). That might be the reason, why Hermann observed
> strange behavior of S-parameters in his experiments.
>
> Best regards,
> Ege Engin
>
> "Loyer, Jeff" schrieb:
> >
> > 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
> > > ------------------------------------------------------------------
> > > To unsubscribe from si-list:
> > > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
> > >=20
> > > or to administer your membership from a web page, go to:
> > > //www.freelists.org/webpage/si-list
> > >=20
> > > For help:
> > > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> > >=20
> > > List technical documents are available at:
> > > http:/www.si-list.org
> > >=20
> > > List archives are viewable at:
> > > //www.freelists.org/archives/si-list
> > > or at our remote archives:
> > > http://groups.yahoo.com/group/si-list/messages
> > > Old (prior to June 6, 2001) list archives are viewable at:
> > > http://www.qsl.net/wb6tpu
> > >=20
> >
> > --
> >
> > -- Binary/unsupported file stripped by Ecartis --
> > -- Type: text/x-vcard
> > -- File: engin.vcf
> > -- Desc: Visitenkarte f=FCr Ege Engin
> >
> > ------------------------------------------------------------------
> > To unsubscribe from si-list:
> > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
> >
> > or to administer your membership from a web page, go to:
> > //www.freelists.org/webpage/si-list
> >
> > For help:
> > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> >
> > List technical documents are available at:
> > http:/www.si-list.org
> >
> > List archives are viewable at: =20
> > //www.freelists.org/archives/si-list
> > or at our remote archives:
> > http://groups.yahoo.com/group/si-list/messages=20
> > Old (prior to June 6, 2001) list archives are viewable at:
> > http://www.qsl.net/wb6tpu
> > =20
> >
> > ------------------------------------------------------------------
> > To unsubscribe from si-list:
> > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
> >
> > or to administer your membership from a web page, go to:
> > //www.freelists.org/webpage/si-list
> >
> > For help:
> > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> >
> > List technical documents are available at:
> > http://www.si-list.org
> >
> > List archives are viewable at:
> > //www.freelists.org/archives/si-list
> > or at our remote archives:
> > http://groups.yahoo.com/group/si-list/messages
> > Old (prior to June 6, 2001) list archives are viewable at:
> > http://www.qsl.net/wb6tpu
> >
>
> --
> Diese E-Mail kann Betriebs- und Geschäftsgeheimnisse, dem
> Anwaltsgeheimnis unterliegende oder sonstige vertrauliche
> Informationen enthalten. Sollten Sie diese E-Mail irrtümlich
> erhalten haben, ist Ihnen die Kenntnisnahme des Inhalts,
> eine Vervielfältigung oder Weitergabe der E-Mail ausdrücklich
> untersagt. Bitte benachrichtigen Sie den Absender der E-Mail
> und vernichten die empfangene E-Mail. Vielen Dank.
>
> Since this e-mail contains confidential information, it must
> be treated with utmost confidentiality. Any person who may
> get in contact with this information by mistake should not
> take any notice of the topic and should not pass on or
> duplicate any part of this information. The e-mail has to be
> destroyed and the sender of the the e-mail has to be informed
> immediately.
> Thank you.
--
Diese E-Mail kann Betriebs- und Geschäftsgeheimnisse, dem
Anwaltsgeheimnis unterliegende oder sonstige vertrauliche
Informationen enthalten. Sollten Sie diese E-Mail irrtümlich
erhalten haben, ist Ihnen die Kenntnisnahme des Inhalts,
eine Vervielfältigung oder Weitergabe der E-Mail ausdrücklich
untersagt. Bitte benachrichtigen Sie den Absender der E-Mail
und vernichten die empfangene E-Mail. Vielen Dank.
Since this e-mail contains confidential information, it must
be treated with utmost confidentiality. Any person who may
get in contact with this information by mistake should not
take any notice of the topic and should not pass on or
duplicate any part of this information. The e-mail has to be
destroyed and the sender of the the e-mail has to be informed
immediately.
Thank you.
-- Binary/unsupported file stripped by Ecartis --
-- Type: text/x-vcard
-- File: engin.vcf
-- Desc: Visitenkarte für Ege Engin
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.org
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
