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

["jun feng" <junfeng.zhou@xxxxxxxxx>]

Hi All,
    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 ?

   One easy solution might be symply taking  the derivative of i(t), then do
FFT analysis. However, it is not feasible because the data is huge for such
a long period. This is why I ask if there is any short cut which I can use
to directly get the spectrum of di/dt from i(t) .

  Hope anyone who had such experience could help me out!  Thanks in advance
,

regards,

Junfeng


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