[SI-LIST] Differential measurement with normal VNA
- From: Matthias Bergmann <MBergmann@xxxxxxxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 6 Apr 2009 15:32:19 +0200
Hello SI-LIST,
I would like to measure a differential structure with a network analyzer
and have got the
following questions:
First I will measure single S-parameters which are afterwards converted
mathematically to
differential S-parameters as described by Bockelmann and Eisenstadt.
1) My VNA measurement system is connected to the DUT by cables and SMA
connectors.
I want to calibrate the network analyzer to the end of the cables using a
standard SMA
calibration kit, but I am not sure if this will be sufficient.
Is there anything like a rule of thumb until which frequency it is
tolerable to neglet the effect of
the connectors and when I have to use a custom-designed calibration ?
2) Shall I design the traces between the differential DUT and the
connectors as tightly-
coupled transmission lines with a differential impedance of 100 Ohms or as
two loosely-
coupled traces with a single impedance of 50 Ohms each one ?
In their books Bogatin and Johnson write that two loosely-coupled traces
with 50 Ohms
indeed have got a differential impedance of 100 Ohms and that tightly
coupled traces are just
used because of limited space on the pcb ? Furthermore I don`t really
understand the
appendix about coupled and uncoupled lines in the original article from
Bockelmann and
Eisenstadt.
3) Assuming that I will use coupled lines:
Probably the differential impedance would reach the aimed 100 Ohms, but the
single impedances would be somewhat higher than 50 Ohms. If I terminate the
unused terminals with 50 Ohms SMA-termination plugs, can I neglet the
imperfect termination or how should the terminatin look like ?
How does the broadening / drift of the traces in the region of the sma
connectors influence the measurement ? Can I neglet this effect ?
Thank you, Matthias
____________________________________
Business Unit Geräteanschlusstechnik
Technologielabor
Dipl.-Ing. Matthias Bergmann
Phoenix Contact GmbH & Co. KG
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Germany
Tel.: ++49 - (0) 5235 3-4 13 85
Fax: ++49 - (0) 5235 3-4 20 02
e-mail: mbergmann@xxxxxxxxxxxxxxxxxx
Internet: www.phoenixcontact.com
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