Inductor Q measurement

[Philip Newman]

Does anyone know how to measure the Q value of an inductor, using
Agilent's ADS? Or any simulation package?

I have a inductor from the SMT library, and it seems to have a higher
Q value than the data sheet says it should have. I want to measure
the Q value and see what I am getting. I am using these inductors to
build a high-order filter and the Q value is important as I need to
obtain a flat pass-band (0.2dB ripple).

If anyone can point me in the right direction, or give my any help in
measuring Q of an inductor, then I would be most grateful.

Thanks

Phil

 

[john jardine]

Does anyone know how to measure the Q value of an inductor, using
Agilent's ADS? Or any simulation package?

I have a inductor from the SMT library, and it seems to have a higher
Q value than the data sheet says it should have. I want to measure
the Q value and see what I am getting. I am using these inductors to
build a high-order filter and the Q value is important as I need to
obtain a flat pass-band (0.2dB ripple).

If anyone can point me in the right direction, or give my any help in
measuring Q of an inductor, then I would be most grateful.

Thanks

Phil

Believe the data sheet. The real inductor is tested under real conditions.
The library inductor can only be an idealised version of the real component.
Many physical design aspects such as loss and skin effect factors can not be
modelled with any accuracy, if at all.
Also, the makers usually supply Q values at only one test frequency. your
filter will no doubt be working at some other frequency and the Q will be
different. Maybe best to grade the components on a commercial Q meter. 2%
ripple is not a lot, and a simple bench Q meter setup (generator, series L,
parr C, AC voltmeter, would not easily offer up the required precision.

 

[BobGardner]

Does anyone know how to measure the Q value of an inductor,
============================
Its just wL/R isnt it? Or resonate it against a known C, measure hi and lo 3dB
down freq points, then compute f0/bw

 

[john jardine]

============================
Its just wL/R isnt it? Or resonate it against a known C, measure hi and lo 3dB
down freq points, then compute f0/bw

Yes it is wL/R but the damned R will refuse to be easily pinned down. A
simple way is to series resonate the inductor and capacitor. That way there
is fewer complications from shunt loading effects dropping the measured Q
value.
Use a signal generator with a 50ohm output. Feed the output voltage to a
47ohm 1ohm potential divider. Feed the circuit from across the 1ohm
resistor. Measure the voltage feeding the circuit (across the 1ohm) and the
magnified resonant voltage across the L or C. Voltage ratio is the Q value
at that test frequency. It's not perfect but it'll get you up and running.
regrds
john