[SI-LIST] Re: From spectrum of i(t) to spectrum of d(i(t))/dt
- From: "Andrew Ingraham" <a.ingraham@xxxxxxxx>
- To: "si-list" <si-list@xxxxxxxxxxxxx>
- Date: Sat, 19 May 2007 10:44:26 -0400
> The differentiation in amperes is not amperes but not unitless,
> either.
Correct.
> The time derivative of the current simply results in "voltage"
> -after a correction factor with the inductance of the medium.
Bzzzt. Sorry, wrong.
Time derivative of current is current/time (amps/sec). It is unrelated to
voltage, unless the current i(t) is passed through a pure inductance and you
measure the voltage v(t) across that inductance; and then whether or not it
is 180dB, happens only for one unique value of that inductance.
While some inductance exists almost everywhere, it is extremely unlikely
that the total load on the power supply is purely inductive. Therefore,
di(t)/dt does not result in v(t), the output voltage of the power supply
(even ignoring DC).
Another note for the original questioner: Taking derivatives does indeed
tend to result in lots of high frequency "noise," and it is necessary to
limit the bandwidth at some point, so that the noise doesn't become
enormous. Take this into consideration, especially with actual
measurements. In analog circuits, there is a reason (this being one of
them) why you often find integrator circuits but rarely find differentiator
circuits.
Regards,
Andy
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