[time-nuts] PLL Math Question

Magnus Danielson magnus at rubidium.dyndns.org
Fri Mar 14 12:43:15 EDT 2014

On 14/03/14 00:39, Bob Camp wrote:
> Hi
> Either grab a math pack (there are several for the PIC) or go to C.
> Timing at the Time Nuts level is about precision. We need *lots* of digits past the binary point :)

Indeed. Throwing bits at the problems is relatively cheap today. 
Besides, you don't process it that often, so you can afford to let a few 
cycles bring you design margin.

Remember, you want the internal resolution to have many bits below the 
single-shot resolution. Lack of bits in frequency resolution tends to 
get you doing bang-bang regulations to approximate the frequency. With 
sufficient resolution other noise sources will assist to average out 
that quantization step. The bang-bang regulations naturally give you an 
idle-frequency, and both frequency and amplitude depends on the 
quantization step.


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