[sdiy] NCO Jitter (was Large Numbers)

[Tim Ressel]

So how much overclocking on the an NCO is needed to reduce the jitter to 
an acceptable level? I will be sampling at 48K. If I run the NCOs at 20x 
that rate, is that good enough?  Keeping in mind I have 10 NCOs to 
operate and a proc running at 180 MHz.

--timster


On 7/13/2018 1:29 PM, Tom Wiltshire wrote:
> The amount of jitter is related to the clock rate, since basically you jitter by having an extra clock cycle occasionally to keep the mean where you need it. E.g. The jitter is one clock period.
>
> Increasing the accumulator size will increase your frequency accuracy, but it won’t reduce the jitter. If you ran a 128-bit NCO at 32KHz, it would jitter like hell but be accurate to fractions of a picohertz. If you ran a 16-bit NCO at 400MHz, it’d have little jitter, but relatively big frequency steps.
>
> Someone please step in if this is not correct - this is my understanding having played with these things a good deal.
>
> Tom
>
>
>> On 13 Jul 2018, at 19:33, Tim Ressel <timr at circuitabbey.com> wrote:
>>
>> If you must pry...  ;-)
>>
>> I am playing with using a 64 bit accumulator in a DCO (NCO?) to fix the top jitter problem. The notion is that increased resolution in the increment value will cause less top jitter.
>>
>> --tr
>>
>>
>> On 7/13/2018 11:30 AM, Richie Burnett wrote:
>>> Out of interest, what application requires table lookup of values to a resolution of better than 1 part in 10 to the 19 !?!?!?
>>>
>>> -Richie,
>>>
>>> Sent from my Xperia SP on O2
>
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-- 
--Tim Ressel
Circuit Abbey
timr at circuitabbey.com