Re: Software PLL (SPLL)

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.

> 
> 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