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 <[email protected]> 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 <[email protected]> >> 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 <[email protected]>: >>> >>> 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 -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
