[SI-LIST] Characteristic Impedance value in frequency domain measurement

[Apig Donaganian]

Dear Experts,


when a time domain engineer works with a VNA will have some struggling issues to understand the measurements. I think the frequency domain gives crucial details what a time domain-er needs.

My question is maybe a kind of primitive one but I need to understand it thoroughly..



Here it is:

Coax Cable

Length : 250 mm

Characteristic Impedance : 50 Ohm

Er= 2.29 (66% Velocity ratio) --> 200 mm /ns



TDR – Time Domain Measurement: (Far End Open)

--> Impedance: around 50 Ohm for a time of 1.25ns (250mm /(200mm/ns) = 1.25ns) then goes the impedance to “infinite” as open End.



VNA – 1-Port Measurement: (Far End Open)

Impedance Value extracted from S11 (Zr @ Keysight) (F-axis: Log, Z-axis: Lin)

High Impedance in low frequencies. The Impedance curve goes down with a capacitive effect (PI-Model) to low impedance range of few Ohms. (in Theory: 0 Ohm @ Lambda/4 and every Lambda/4 + n x Lambda/2)

Afterwards comes the first lambda/2 - Peak @ 400MHz: (1/(2x1,25ns)) and then every (n x Lambda/2)

and this repeats itself in inductive and capaitive manner.



so i was trying to find the charactersitic Z or 50 Ohm in this measurement and found it at Lambda/8 and then every (Lambda/8 + Lambda /4). i tried also with other cables in different lengths... always the same..


what kind of information is this? what is the relationship between Lambda/8 and the characteristic Impedance?


i haven't found this detail in any transmission line Book (Wadell, Pozar, Clayton, etc.) so i thought it may be its better to ask here if anybody can help me to understand.



Thank you in advance for you helpful answers,



Best Regards from Germany,



apig






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[Orin Laney]

The difference between time domain reflection and frequency domain scatter
is at work here. Suffice to say, if you are interested in the impedance of
the cable itself, the number seen on the TDR before the first reflection
arrives is the correct number. If you are interested in the impedance of the
whole shebang including all the reflections, then the VNA number is what you
want as long you are OK with the fact that it varies with frequency. These
are two very different impedance concepts. You can't reconcile them because
they aren't two views of the same thing.

Orin

-----Original Message-----
From: si-list-***@freelists.org [mailto:si-list-***@freelists.org] On
Behalf Of Apig Donaganian
Sent: Saturday, November 17, 2018 10:40 AM
To: si-***@freelists.org
Subject: [SI-LIST] Characteristic Impedance value in frequency domain
measurement

Dear Experts,


when a time domain engineer works with a VNA will have some struggling
issues to understand the measurements. I think the frequency domain gives
crucial details what a time domain-er needs.

My question is maybe a kind of primitive one but I need to understand it
thoroughly..



Here it is:

Coax Cable

Length : 250 mm

Characteristic Impedance : 50 Ohm

Er= 2.29 (66% Velocity ratio) --> 200 mm /ns



TDR - Time Domain Measurement: (Far End Open)

--> Impedance: around 50 Ohm for a time of 1.25ns (250mm /(200mm/ns) =
1.25ns) then goes the impedance to "infinite" as open End.



VNA - 1-Port Measurement: (Far End Open)

Impedance Value extracted from S11 (Zr @ Keysight) (F-axis: Log, Z-axis:
Lin)

High Impedance in low frequencies. The Impedance curve goes down with a
capacitive effect (PI-Model) to low impedance range of few Ohms. (in Theory:
0 Ohm @ Lambda/4 and every Lambda/4 + n x Lambda/2)

Afterwards comes the first lambda/2 - Peak @ 400MHz: (1/(2x1,25ns)) and
then every (n x Lambda/2)

and this repeats itself in inductive and capaitive manner.



so i was trying to find the charactersitic Z or 50 Ohm in this measurement
and found it at Lambda/8 and then every (Lambda/8 + Lambda /4). i tried also
with other cables in different lengths... always the same..


what kind of information is this? what is the relationship between Lambda/8
and the characteristic Impedance?


i haven't found this detail in any transmission line Book (Wadell, Pozar,
Clayton, etc.) so i thought it may be its better to ask here if anybody can
help me to understand.



Thank you in advance for you helpful answers,



Best Regards from Germany,



apig






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[Tom Dagostino]

With a TDR system, the result is an impedance plot vs. time (distance) from
the TDR connection to the DUT. If the impedance is of a 50 Ohm low loss
cable then you would expect to see a impedance of 50 Ohms from the near end
of the cable to the far end where in your example which is open, the
impedance jumps to infinity.

With the VNA in your setup you are looking at the impedance as seen at the
input of the coax only. At the input you see the characteristic impedance
of the coax plus the effects of all the reflections, in this case the
reflections off the open end. So your DUT looks like a stub which has a
varying impedance vs. frequency. When all the reflections cancel each other
you will see the Zo of the cable.

So, TDR is distributed impedance and a VNA is in this case impedance at a
single point as modified by reflections.

Tom Dagostino
971-279-5325
***@teraspeedlabs.com

Teraspeed Labs
9999 SW Wilshire Street
Suite 102
Portland, OR 97225


-----Original Message-----
From: si-list-***@freelists.org [mailto:si-list-***@freelists.org] On
Behalf Of Apig Donaganian
Sent: Saturday, November 17, 2018 10:40 AM
To: si-***@freelists.org
Subject: [SI-LIST] Characteristic Impedance value in frequency domain
measurement

Dear Experts,


when a time domain engineer works with a VNA will have some struggling
issues to understand the measurements. I think the frequency domain gives
crucial details what a time domain-er needs.

My question is maybe a kind of primitive one but I need to understand it
thoroughly..



Here it is:

Coax Cable

Length : 250 mm

Characteristic Impedance : 50 Ohm

Er= 2.29 (66% Velocity ratio) --> 200 mm /ns



TDR - Time Domain Measurement: (Far End Open)

--> Impedance: around 50 Ohm for a time of 1.25ns (250mm /(200mm/ns) =
1.25ns) then goes the impedance to "infinite" as open End.



VNA - 1-Port Measurement: (Far End Open)

Impedance Value extracted from S11 (Zr @ Keysight) (F-axis: Log, Z-axis:
Lin)

High Impedance in low frequencies. The Impedance curve goes down with a
capacitive effect (PI-Model) to low impedance range of few Ohms. (in Theory:
0 Ohm @ Lambda/4 and every Lambda/4 + n x Lambda/2)

Afterwards comes the first lambda/2 - Peak @ 400MHz: (1/(2x1,25ns)) and
then every (n x Lambda/2)

and this repeats itself in inductive and capaitive manner.



so i was trying to find the charactersitic Z or 50 Ohm in this measurement
and found it at Lambda/8 and then every (Lambda/8 + Lambda /4). i tried also
with other cables in different lengths... always the same..


what kind of information is this? what is the relationship between Lambda/8
and the characteristic Impedance?


i haven't found this detail in any transmission line Book (Wadell, Pozar,
Clayton, etc.) so i thought it may be its better to ask here if anybody can
help me to understand.



Thank you in advance for you helpful answers,



Best Regards from Germany,



apig






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[Istvan Novak]

Hi Apig,

The answer to your question is very simple.  What you observe, the
agreement of input impedance and characteristic impedance when the
transmission line is one eights of the wavelength or of its harmonics,
is pure coincide.  At those frequencies the tangent function yields one
in the formula which gives you the input impedance.  This is covered in
the books you listed, though probably not directly in the contexts how
you posed the question.

A few specific details, which matter when you take a closer look:

- from TDR you get the characteristic impedance, which is dominantly a
real number for low-loss transmission lines

- from a VNA measurement of an unterminated transmission line you get
the open-terminated input impedance, which is a dominantly imaginary
number, but its absolute value happens to equal the characteristic
impedance when the phase shift through the transmission line is 45
degrees or the appropriate multiples.

Thanks

Istvan

Post by Apig Donaganian
Dear Experts,
when a time domain engineer works with a VNA will have some struggling issues to understand the measurements. I think the frequency domain gives crucial details what a time domain-er needs.
My question is maybe a kind of primitive one but I need to understand it thoroughly..
Coax Cable
Length : 250 mm
Characteristic Impedance : 50 Ohm
Er= 2.29 (66% Velocity ratio) --> 200 mm /ns
TDR – Time Domain Measurement: (Far End Open)
--> Impedance: around 50 Ohm for a time of 1.25ns (250mm /(200mm/ns) = 1.25ns) then goes the impedance to “infinite” as open End.
VNA – 1-Port Measurement: (Far End Open)
and this repeats itself in inductive and capaitive manner.
so i was trying to find the charactersitic Z or 50 Ohm in this measurement and found it at Lambda/8 and then every (Lambda/8 + Lambda /4). i tried also with other cables in different lengths... always the same..
what kind of information is this? what is the relationship between Lambda/8 and the characteristic Impedance?
i haven't found this detail in any transmission line Book (Wadell, Pozar, Clayton, etc.) so i thought it may be its better to ask here if anybody can help me to understand.
Thank you in advance for you helpful answers,
Best Regards from Germany,
apig
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["Vinu Arumugham" (Redacted sender "vinua" for DMARC)]

TDR gives you transient response, characteristic impedance.


VNA gives you steady state response, driving point impedance or input
impedance or effective impedance.


Thanks,

Vinu

Post by Apig Donaganian
Dear Experts,
when a time domain engineer works with a VNA will have some struggling issues to understand the measurements. I think the frequency domain gives crucial details what a time domain-er needs.
My question is maybe a kind of primitive one but I need to understand it thoroughly..
Coax Cable
Length : 250 mm
Characteristic Impedance : 50 Ohm
Er= 2.29 (66% Velocity ratio) --> 200 mm /ns
TDR – Time Domain Measurement: (Far End Open)
--> Impedance: around 50 Ohm for a time of 1.25ns (250mm /(200mm/ns) = 1.25ns) then goes the impedance to “infinite” as open End.
VNA – 1-Port Measurement: (Far End Open)
and this repeats itself in inductive and capaitive manner.
so i was trying to find the charactersitic Z or 50 Ohm in this measurement and found it at Lambda/8 and then every (Lambda/8 + Lambda /4). i tried also with other cables in different lengths... always the same..
what kind of information is this? what is the relationship between Lambda/8 and the characteristic Impedance?
i haven't found this detail in any transmission line Book (Wadell, Pozar, Clayton, etc.) so i thought it may be its better to ask here if anybody can help me to understand.
Thank you in advance for you helpful answers,
Best Regards from Germany,
apig
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[a***@wildrivertech.com]

Read "Resonant Test Structures: Primer and Signal Integrity Applications" from Tim Wang Lee/Al Neves on WRT website

I relates resonance (S-parameters) to topological length (directly measured TDR).






Products for the Signal Integrity Practitioner

Alfred P. Neves
Chief Technology Officer

- EDA Simulation to Measurement Tools
- Stellar Signal Integrity Design up to 70GHz
- Serial Link Testing through 112G PAM-4

Office (In PST zone): 503-679-2429
www.wildrivertech.com

-----Original Message-----
From: si-list-***@freelists.org <si-list-***@freelists.org> On Behalf Of Vinu Arumugham (Redacted sender "vinua" for DMARC)
Sent: Monday, November 19, 2018 4:05 PM
To: si-***@freelists.org
Subject: [SI-LIST] Re: Characteristic Impedance value in frequency domain measurement

TDR gives you transient response, characteristic impedance.


VNA gives you steady state response, driving point impedance or input impedance or effective impedance.


Thanks,

Vinu

Post by Apig Donaganian
Dear Experts,
when a time domain engineer works with a VNA will have some struggling issues to understand the measurements. I think the frequency domain gives crucial details what a time domain-er needs.
My question is maybe a kind of primitive one but I need to understand it thoroughly..
Coax Cable
Length : 250 mm
Characteristic Impedance : 50 Ohm
Er= 2.29 (66% Velocity ratio) --> 200 mm /ns
TDR – Time Domain Measurement: (Far End Open)
--> Impedance: around 50 Ohm for a time of 1.25ns (250mm /(200mm/ns) = 1.25ns) then goes the impedance to “infinite” as open End.
VNA – 1-Port Measurement: (Far End Open)
and this repeats itself in inductive and capaitive manner.
so i was trying to find the charactersitic Z or 50 Ohm in this measurement and found it at Lambda/8 and then every (Lambda/8 + Lambda /4). i tried also with other cables in different lengths... always the same..
what kind of information is this? what is the relationship between Lambda/8 and the characteristic Impedance?
i haven't found this detail in any transmission line Book (Wadell, Pozar, Clayton, etc.) so i thought it may be its better to ask here if anybody can help me to understand.
Thank you in advance for you helpful answers,
Best Regards from Germany,
apig
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[Apig Donaganian]

thank you everybody for your helpful comments... i think i am getting by time more familiar with frequency domain...

thank you Al for sharing the link... great job and good described...


best Regards,


apig


________________________________
Von: si-list-***@freelists.org <si-list-***@freelists.org> im Auftrag von ***@wildrivertech.com <***@wildrivertech.com>
Gesendet: Dienstag, 20. November 2018 01:36
An: dmarc-***@freelists.org; si-***@freelists.org
Cc: Tim Horel
Betreff: [SI-LIST] Re: Characteristic Impedance value in frequency domain measurement

Read "Resonant Test Structures: Primer and Signal Integrity Applications" from Tim Wang Lee/Al Neves on WRT website

I relates resonance (S-parameters) to topological length (directly measured TDR).






Products for the Signal Integrity Practitioner

Alfred P. Neves
Chief Technology Officer

- EDA Simulation to Measurement Tools
- Stellar Signal Integrity Design up to 70GHz
- Serial Link Testing through 112G PAM-4

Office (In PST zone): 503-679-2429
www.wildrivertech.com<http://www.wildrivertech.com>
[Loading Image...]<http://www.wildrivertech.com/>

Home [wildrivertech.com]<http://www.wildrivertech.com/>
www.wildrivertech.com
"The CMP-28 platform from Wild River Technology is a versatile channel modeling platform. During my recent research into modeling conductor surface roughness, I relied on trusted measurement data for simulation correlation, and achieved excellent results."



-----Original Message-----
From: si-list-***@freelists.org <si-list-***@freelists.org> On Behalf Of Vinu Arumugham (Redacted sender "vinua" for DMARC)
Sent: Monday, November 19, 2018 4:05 PM
To: si-***@freelists.org
Subject: [SI-LIST] Re: Characteristic Impedance value in frequency domain measurement

TDR gives you transient response, characteristic impedance.


VNA gives you steady state response, driving point impedance or input impedance or effective impedance.


Thanks,

Vinu

Post by Apig Donaganian
Dear Experts,
when a time domain engineer works with a VNA will have some struggling issues to understand the measurements. I think the frequency domain gives crucial details what a time domain-er needs.
My question is maybe a kind of primitive one but I need to understand it thoroughly..
Coax Cable
Length : 250 mm
Characteristic Impedance : 50 Ohm
Er= 2.29 (66% Velocity ratio) --> 200 mm /ns
TDR – Time Domain Measurement: (Far End Open)
--> Impedance: around 50 Ohm for a time of 1.25ns (250mm /(200mm/ns) = 1.25ns) then goes the impedance to “infinite” as open End.
VNA – 1-Port Measurement: (Far End Open)
and this repeats itself in inductive and capaitive manner.
so i was trying to find the charactersitic Z or 50 Ohm in this measurement and found it at Lambda/8 and then every (Lambda/8 + Lambda /4). i tried also with other cables in different lengths... always the same..
what kind of information is this? what is the relationship between Lambda/8 and the characteristic Impedance?
i haven't found this detail in any transmission line Book (Wadell, Pozar, Clayton, etc.) so i thought it may be its better to ask here if anybody can help me to understand.
Thank you in advance for you helpful answers,
Best Regards from Germany,
apig
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[alfred1520list]

I hope this alternative presentation can give a different insight to the difference.
Both Alfred and Vinu's posts hint at the difference. In TDR the measurement is stopped once the first reflection has reached the measuring requirement.

In VNA measurement the reflection is allowed to setup constructive or destructive standing waves, so the cable appears as opened or shorted, at the fundamental and all higher resonant frequencies up to the high frequency limit of the measurement equipment.

Happy Thanksgiving,
Alfred Lee

Post by Apig Donaganian
thank you everybody for your helpful comments... i think i am getting
by time more familiar with frequency domain...
thank you Al for sharing the link... great job and good described...
best Regards,
apig
________________________________
Gesendet: Dienstag, 20. November 2018 01:36
Cc: Tim Horel
Betreff: [SI-LIST] Re: Characteristic Impedance value in frequency domain measurement
Read "Resonant Test Structures: Primer and Signal Integrity
Applications" from Tim Wang Lee/Al Neves on WRT website
I relates resonance (S-parameters) to topological length (directly measured TDR).
Products for the Signal Integrity Practitioner
Alfred P. Neves
Chief Technology Officer
- EDA Simulation to Measurement Tools
- Stellar Signal Integrity Design up to 70GHz
- Serial Link Testing through 112G PAM-4
Office (In PST zone): 503-679-2429
www.wildrivertech.com<http://www.wildrivertech.com>
[http://wildrivertech.com/components/com_rsmediagallery/assets/gallery/original/9fb0c1ef88223349a1ea7c75e4060014.jpg]<http://www.wildrivertech.com/>
Home [wildrivertech.com]<http://www.wildrivertech.com/>
www.wildrivertech.com
"The CMP-28 platform from Wild River Technology is a versatile channel
modeling platform. During my recent research into modeling conductor
surface roughness, I relied on trusted measurement data for simulation
correlation, and achieved excellent results."
-----Original Message-----
Behalf Of Vinu Arumugham (Redacted sender "vinua" for DMARC)
Sent: Monday, November 19, 2018 4:05 PM
Subject: [SI-LIST] Re: Characteristic Impedance value in frequency domain measurement
TDR gives you transient response, characteristic impedance.
VNA gives you steady state response, driving point impedance or input
impedance or effective impedance.
Thanks,
Vinu

Post by Apig Donaganian
Dear Experts,
when a time domain engineer works with a VNA will have some

struggling issues to understand the measurements. I think the frequency
domain gives crucial details what a time domain-er needs.

Post by Apig Donaganian
My question is maybe a kind of primitive one but I need to understand

it thoroughly..

Post by Apig Donaganian
Coax Cable
Length : 250 mm
Characteristic Impedance : 50 Ohm
Er= 2.29 (66% Velocity ratio) --> 200 mm /ns
TDR ￜ Time Domain Measurement: (Far End Open)
--> Impedance: around 50 Ohm for a time of 1.25ns (250mm /(200mm/ns)

= 1.25ns) then goes the impedance to ￜinfiniteￜ as open End.

Post by Apig Donaganian
VNA ￜ 1-Port Measurement: (Far End Open)

Z-axis: Lin)

Post by Apig Donaganian
High Impedance in low frequencies. The Impedance curve goes down with

a capacitive effect (PI-Model) to low impedance range of few Ohms. (in
and then every (n x Lambda/2)

Post by Apig Donaganian
and this repeats itself in inductive and capaitive manner.
so i was trying to find the charactersitic Z or 50 Ohm in this

measurement and found it at Lambda/8 and then every (Lambda/8 + Lambda
/4). i tried also with other cables in different lengths... always the
same..

Post by Apig Donaganian
what kind of information is this? what is the relationship between

Lambda/8 and the characteristic Impedance?

Post by Apig Donaganian
i haven't found this detail in any transmission line Book (Wadell,

Pozar, Clayton, etc.) so i thought it may be its better to ask here if
anybody can help me to understand.

Post by Apig Donaganian
Thank you in advance for you helpful answers,
Best Regards from Germany,
apig
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