[time-nuts] Next upgrade

[EWKehren at aol.com]

As I said in my original post from our point of view there are only two  
reasons for a Rb time and 16 bits will do the job.  I would not do an OCXO  
with less than 22 bits if analog at all.
Bert Kehren
 
 
In a message dated 11/26/2017 8:56:51 A.M. Eastern Standard Time,  
opronningen at gmail.com writes:

I guess  everyone has seen this, but Linear has a nice appnote «A Standards 
Lab Grade  20-Bit DAC with 0.1ppm/°C  Drift»

http://cds.linear.com/docs/en/application-note/an86f.pdf

Ole

>  26. nov. 2017 kl. 13:50 skrev Magnus Danielson  
<magnus at rubidium.dyndns.org>:
> 
> Hi
> 
>>  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.
> 
> Cheers,
> Magnus
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