[time-nuts] Next upgrade

Magnus Danielson magnus at rubidium.dyndns.org
Sun Nov 26 08:50:52 EST 2017


On 11/26/2017 02:26 PM, Attila Kinali wrote:
> Though, if you have a decent 16bit DAC and want to get to 18bit,
> that's fairly simple using delta-sigma modulation... if you can live
> with a low pass fillter after the DAC. But the DNL will be the limiting
> factor here (unless you use some special techniques) and the (absolute) INL
> will not get better, for obvious reasons.

I needed 19 bit rather than 16 bit, so I implemented an interpolation 
scheme. A first degree sigma-delta would also be possible, but for low 
ratios what I did was more efficient.

A first degree sigma-delta is fairly simple thought.

The trick is that you want to push the noise high up so it becomes 
trivial to filter, then the filter will not be hard to design and won't 
be low enough to cause PLL instability and implementation troubles.


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