> 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.
>
> IMHO. YMMV.
I've seen a guy develop a PLL by using an FFT, in a pic. he had learned
about FFTs at uni, but never learned about PLLs. the code eventually
worked....after a year or so.
Cheers
Terry