Hi:

In some papers, they reported their extracted inductance. And the inductance decrease with the increase of frequency.

However, according to some other papers, the inductance increased. What's the difference in their used method of extraction?

I knows only attached one which L increase with F.

Thanks.

Hi,
pancho's answer is completely correct although it doesn't conflict with the reported measurements where inductance increases with frequency. I think that in fact if you made(or simulate) a wide bandwidth with an EM simulator you end up with 3 zones:
1.In the first one as pancho explains the internal inductance goes down due to skin effect.
2.Then when the internal inductance it's negligible due to skin effect inductance will eventually go up again.
3.Inductance will reach a maximum at self-ressonance frequency and then it will start to decrease again.
This can be seen(except probably first zone because it will be needed a series resistance varying with frequency,modelling the skin effect) with a lumped pi model of the inductor and using the formula you provided: for low frequency the imaginary part(since we cannot differentiate between inductive and capacitive components) increases since it's dominated by w*L, from resonance the capacitive part starts to dominate the imaginary part so it changes the slope and it starts to decrease.
I suppose the best measurement will involve a measurement of V and I and calculate L from v=Ldi/dt but with Y,Z or S parameters you cannot obtain this directly.
Hope it helps,

Thanks for the replies.

I understand that inductance will seek minimum "impedance" path, and reduces its inductance in higher frequency. But, how people could extract the real inductance from measured S-parameters?

Hi,
As pancho said  we are measuring a black box(an inductance is something teorical in the end), and as email_gz said why do you want physical inductance instead of apparent inductance?For example look at the following attachment of what they provide to you as an inductor:
First one is a discrete inductor from Murata, second one it's a family of inductors from Coilcraft and last it's a capture from a presentation of UMC about how they made their inductors available at: http://www.ansoft.com/deliveringperformance/UMC2.pdf(all this material it's freely available at the web so no NDA problems here).
So in fact what every manufacturer provides it's a table or graph with the apparent inductance and Q factor at different frequencies because it's what you care about when making a circuit.
Hope it helps,

See http://www.designers-guide.org/Forum/YaBB.pl?num=1133858081/1#1

This is for floating inductor.

port1 >---Inductor ----< port2

L1 is inductance evaluated with port2=gnd.
L2 is inductance evaluated with port1=gnd.

L1 = imag(1/y11)/(2*pi*xval(y11))
L2 = imag(1/y22)/(2*pi*xval(y22))  

Q1 = imag(1/y11)/real(1/y11)  
Q2 = imag(1/y22)/real(1/y22)

This is Qdiff, Ldiff and Zdiff=Rdiff+j*Xdiff.
Here Ldiff increase with frequency except for first resonance point.

pancho_hideboo wrote on Apr 1^st, 2008, 12:07am:


Hi, thanks for the detailed information.
Would you kindly provide any reference to the equations used for calculating L using S parameters (both floating and differential )?
thanks.