.MEAS AC How is it done

QSPICE
1

I’m trying to measure the Q factor in some resonance circuits, but it seems like .meas statements are not supported in AC analysis.

Is this observation correct?
If not how is it done?

Br. Marc

2

You can setup .meas to measure Q-factor from bode plot. Q=fo/BW in bode, and you have to setup .meas to get fo and BW. Here is an example for your reference.

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image1879×988 199 KB

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3

As forum is not yet support upload of .qsch, here is formula you can copy. Depends on your situation, you may modify it to work in your schematic.

.meas Vmax max mag(V(out))
.meas fo FIND frequency WHEN mag(V(out))=Vmax 
.meas fL FIND frequency WHEN mag(V(out))=Vmax/sqrt(2) rise=1
.meas fH FIND frequency WHEN mag(V(out))=Vmax/sqrt(2) fall=last
.meas BW fH-fL 
.meas Q fo/BW
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4

It works thanks a lot!!