[sdiy] Q?

[jhaible at debitel.net]

> Now, what is your way to introduce Q?
> 
> My way was to start with a 2nd order bandpass , and define Q as the ratio of
> peak frequency
> versus f1-f2 , where f1 and f2 are the -3dB or half power frequencies.


That's the most convenient definition for AC Spice analysis.

> Are there other ways to do it?

There are definitions in the time domain, based on decay of the ringing of the
filter when excited with a pulse or step.

I think for 2pole BPFs the two definitions mean the same thing.

For higher order filters, you have individual Q's for the individual
pole pairs. (I don't know if there is a definition of Q for the overall response
of a higher order filter. If there's something like that, I never use it.)

JH.

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