[SI-LIST] Spiral inductor L and Q measurement with VNA
- From: rmartinez@xxxxxx (Rafael Martinez)
- To: <si-list@xxxxxxxxxxxxx>
- Date: Thu, 7 Mar 2002 13:03:28 -0000
Hi there,
I am a postgraduate student and I need to design a couple of PCB printed
spiral inductors for my project. After a lot of work simulating I decided to
measure the inductor in the "real world". I´ve never used a VNA before, and
of course I've never designed a test fixture for measuring spiral inductors.
Anyway, I trusted in my "common sense" and I designed something similar to a
test fixture...
I selected SMA connectors, I do not know exactly why, I believe it was
because I saw them in several test fixtures.
One thing I knew was that the trace impedance had to be 50Ohms to match the
impedance of the VNA ports and so, reduce the reflections on the interfaces.
I chose coplanar line because I could use narrower traces. And nothing else,
I put my spiral inductor in the text fixture as follows:
square
50Ohms CPW hole
______________ _______________
SMA 0************** -@- ***************0 SMA
______________ || _______________ gnd
square hole with vias inside it
where:
0 is the connector
___
*** is the 50 Ohms coplanar line
-@- is the spiral inductor
| represents vias
_ is the ground plane
Since I am using coplanar lines, I opened a square hole in the top and in
the bottom layer to place the inductor in the middle of it (I had to open
two vias to acces to the bottom layer and another to come back again to the
top layer). The edges of that square hole would define my reference plane.
Furthermore, I did the three calibration standart O-S-L-T
______________
SMA 0************** OPEN
______________ gnd
______________
SMA 0**************|| SHORT
gnd ______________||
______________#|
SMA 0**************# 50 Ohms (two 100Ohms in parallel)
#|
gnd _______________| vias to ground in both sides
__________________________________
SMA 0**********************************0 (TRHU)
__________________________________ gnd
What I am thinking now, and it is my main concern is that I will have
important reflexions in the connectors...
Another issue to take into account is that the widthness of the spiral trace
is 150microns and the widthness of the coplanar line is around 800microns.
So, I will have an impedance change and therefore more reflexions. I think I
should have design that change gradually trying to keep 50Ohms in the
coplanar line, but now is a bit late to do that. I will include that in the
next design. Any advice on this?
I am also very confused in the way I should calibrate the VNA. I know I need
the calibration kit to calibrate the cables. But I am not enterely sure how
to calibrate my test fixture with the calibration fixtures that I designed.
As far as I know, each calibration standard has a standar definition that
describes the electrical characteristics (delay, attenuation and impedance)
I mean, a list of parameters that are used by the VNA to specify the
mathematical model. I am wondering if I have to measure them... if yes how
can I do it?
All comments, references and advices are more than welcome.
Thank you very much in advance.
___________________________________________________________________
Rafael Martinez Catala Rossa Avenue, Bishopstown,
Postgraduate Research Student Cork, Ireland
Cork Institute of Technology Fax: +353 21 4326625
Electronic Engineering Dep. Tel: +353 21 4326881
http://www.cit.ie
___________________________________________________________________
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