Hi Each time I’ve tried the method in the app note, there has been a tone in the output spectrum at the sample rate of the ADC. I’ve never found a way to do the grounding that eliminates it. The tone is large enough to show up as a spur on a “typical” OCXO when it goes into the EFC port.
Bob > On Nov 26, 2017, at 8:56 AM, Ole Petter Rønningen <opronnin...@gmail.com> > wrote: > > 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 <mag...@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 >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
