...and what about shrinking the 16bit over the fraction of the EFC range that, for example, the OCXO will be using for the next 5 years? 16bit over 10V are as 20 (a little less, OK) over 1V, if I can use my 16bit over 1V for the next 5 years, when the DAC will be near full scale I can "trim" the aging.
On Sun, Nov 26, 2017 at 6:25 PM, Bob kb8tq <kb...@n1k.org> wrote: > Hi > > If you sum two DAC’s without any sort of feedback, you get problems when the > “coarse” dac is changed. You have no way to know the step size of the coarse > dac to (say) 20 bit precision. > > As an example : If you are after 20 “good” bits, you might overlap > them at the 10 bit point on the coarse dac. That would give you 22 bits on the > summed output. It would give you enough extra bits to take care of any odd > things that might be going on. You only have 1/1024 of the total range before > you must tune the coarse dac. Even with a good set of parts, you *will* be > doing coarse tuning. > > Bob > >> On Nov 26, 2017, at 12:13 PM, Azelio Boriani <azelio.bori...@gmail.com> >> wrote: >> >> Is summing a "fine tune" 16bit DAC and a "coarse tune" 16bit (or less) >> DAC with an op-amp not good enough? >> >> On Sun, Nov 26, 2017 at 5:53 PM, Bob kb8tq <kb...@n1k.org> wrote: >>> 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. >> _______________________________________________ >> 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.
