[sdiy] DCO Question

[Mattias Rickardsson]

On 6 November 2017 at 17:04, Gordonjcp <gordonjcp at gjcp.net> wrote:

> >
> > > >> Well, it also hasn't got partials extending off to infinity,
> otherwise
> > > >> you'd need an infinitely powerful power supply ;-)
> > > >
> > > > Why? Infinite series often have finite sums.
> > >
> > > Of course, but gjcp was not talking about any old series, but the
> > > sawtooth specifically.
> >
> > I'd say an analog sawtooth *has* got partials extending off to infinity
> > (why would they suddenly come to an end?), but in a more decaying rate
> than
> > a perfect sawtooth - resulting in a sum that is finite.
>
> Because your circuit hasn't got infinite bandwidth.  You won't find much
> breaking the noise floor above a few hundred kHz.
>

The partials are still there, down in the noise floor. Specifying the
concept of a bandwidth in terms of how wide part of the spectrum is above a
certain level doesn't magically remove or prevent signals outside this
bandwidth.

The noise energy is *added* to the energy of the partials, so your noisy
version of the sawtooth has *more* energy than the clean sawtooth that you
feared would need an infinitely powerful power supply. :-)

/mr
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