Re: Software PLL (SPLL)

Terry Given wrote:
> Ron N. wrote:
> > Terry Given wrote:
> >
> >>Ron N. wrote:
> >>
> >>>Tim Wescott wrote:
> >>>
> >>>>Implementing a PLL in software uses the same basic theory as
> >>>>implementing a PLL in hardware -- you compare your synthesized signal to
> >>>>a reference, generate a phase difference, then servo the frequency of
> >>>>your synthesized signal to your reference.
> >
> > ...
> >
> >>>Why?  Isn't a software PLL just a forward interpolator.  Why not just
> >>>estimate (statistical, FFT, phase vocoder or otherwise) the frequency,
> >>>phase, derivatives of phase, etc.; generate a forward interpolation of
> >>>the input reference using that information, and call that the output of
> >>>the PLL NCO?  Recalculate periodically (every sample if the compute
> >>>power is available).
> >
> > ...
> >
> >>you would have to work quite very to match, let alone beat, the
> >>performance you can get from a software PLL, requiring negligible
> >>computational overhead.
> >>
> >>swatting flies with Howitzers often causes more problems than it solves.
> >
> >
> > If a simple feedback PLL is such a good solution, why isn't it used
> > more often for general frequency estimation and interpolation
> > problems?
>
> oh, here I was thinking PLLs abound. best not to mention this to the
> entire telecommunications and control industries.

Why would one not think that the use of feedback PLLs abound?

But I note that the use of fft's, autocorrelation and other statistical
techniques are also popular for many problems where the analysis
of only one fundamental frequency is of interest.  Why use one
technique and not the other?  Where are the limits of applicability
for feedback PLLs, and have those limits changed with the order
of magnitude changes in MACs per dollar?


IMHO. YMMV.
-- 
rhn A.T nicholson d.0.t C-o-M