[SOLVED] how to get the Q facator of inductor V.S. frequency curve?

[shanmei]

how to get the Q facator of inductor V.S. frequency curve in cadence?


Anyone has some ideas? Thanks.

 

[Dominik Przyborowski]

My first thought. Connect idc with dc current=1 and ac=1 to shunting inductor. From dc analysis you get resistance value as voltage drop on net connecting idc with your inductor. From AC analysis You will obtain impedance of inductor. Quality factor is Q=wL/R, so using simple formula (VF("/Net1")/VDC("/Net1"))-1 You should get quality factor of inductor, where Net1 is the net connecting idc with inductor. Of course it's a more complicated if some capacitance exist, but for the first order it should be ok.
You can also check in virtuoso calculator that is any function for it.

 

[FvM]

R isn't Rdc, it's the real part of the inductor impedance at actual frequency (reflecting skin effect and core losses).

Respectively Q is abs(im(Vac)/Re(Vac))

 

[shanmei]

I use a idc source to give a 1A current to sweep the frequency. and the figure looks like this:



Thanks, Dominik Przyborowski and FvM.

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By the way, do you think cadence/spectre simulation can simulate the inductor impedance by relecting skin effect and core losses? Thanks. FvM

R isn't Rdc, it's the real part of the inductor impedance at actual frequency (reflecting skin effect and core losses).

Respectively Q is abs(im(Vac)/Re(Vac))

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From the above figure, it shows that at `1GHz, the Q is about 3, quite low. Does it mean it is not good for application at 3GHz? Thanks.

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So the inductor is only good for using at peak Q area. For example, if it is used at 10Mhz, where the Q is quite small, it can't oscillate with a LC tank?

 

[FvM]

You didn't tell any details about your inductor under test, so it's hard to know if the curve is plausible. I would always perform a hand calculation to check the numbers.