FreeLists / si-list / [SI-LIST] Re: From spectrum of i(t) to spectrum of d(i(t))/dt

["Andrew Ingraham" <a.ingraham@xxxxxxxx>]

>     I have some questions on the spectrum translation. Recently, I measured
> the spectrum of power supply current i(t) ( very long time range ) with
> current probes, then I would like to transfer it to the spectrum of di/dt. I
> know thoeretically F( di(t)/dt ) = j w F ( i(t) ). My question is : Does it
> mean at every frequency point, the spectrum level is multiplied by the
> corresponding frequency for di/dt signal ?  If this is the case, the I end
> up with quite large spectrum value in di/dt which is definitly not
> reasonable.  For instance, at 1 GHz, the spectrum level is increase by 180
> dB.  I am quite confused about this.  Is my derivation wrong ?

Yes, it is correct; no your calculation is not wrong.

Take care of your units!  When you differentiate amperes, the result is not in
amperes.  The spectrum contribution at 1 GHz doesn't increase by 180 dB
because that would be "comparing apples to oranges," even though the raw
(unit-less) numbers might happen to be that way.

Andy


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