[sdiy] Waveform analysis into non-sine components

[David G Dixon]

> > I see two things that make the Fourier basis very special:
> > * It is the basis of eigenfunctions of LTI (linear time-invariant) 
> > systems. The LTI bit: Electronic circuits built with ideal R, L, C 
> > elements and linear gain elements (ideal op-amps, OTA, 
> etc...) are LTI 
> > systems - systems whose behavior is captured in a transfer function.
> 
> This nicely segues into the Laplace transform:
> 
> http://en.wikipedia.org/wiki/Laplace_transform
> 
> which is where the 's' operator so often used in filter 
> design comes from.

Fourier transforms are just Laplace transforms for cyclic responses, where
the Laplace variable defined explicitly in terms of the frequency.