Hi Ok, but thats “high pass in the RF section”. You really do not have an audio high pass filter the way you would in a more typical DMTD.
If it’s any comfort, I’m sitting here looking at a very different box. It also has “wobbles” as you get into parts in 10^-16. That might change a bit if the draft coming through the window was a bit less. Bob > On Feb 23, 2020, at 6:12 PM, Jan-Derk Bakker <jdbak...@gmail.com> wrote: > > Dear Bob, > > The capacitors are 47n NP0/C0G types (Kemet C0805C473K3GAC7800), picked for > low tempco (and low DF and other non-ideal behavior). I've not spotted any > hysteresis artefacts in these in previous designs, but I haven't measured > their performance in this circuit. > > Forgot to mention in the previous message: the baluns are transformers > (M/A-COM MABAES0060), so the only DC the ADC should see is its own input > offset (plus offset current across the 25R input filter resistors). Full > schematic is here ( http://www.lartmaker.nl/time-nuts/DMTD_rev0.99.pdf > <http://www.lartmaker.nl/time-nuts/DMTD_rev0.99.pdf> ; needs cleanup, but all > connections are there). > > JDB. > > On Sun, Feb 23, 2020 at 10:13 PM Bob kb8tq <kb...@n1k.org > <mailto:kb...@n1k.org>> wrote: > Hi > > What does the temperature coefficient of your “hardware HPF” filter caps look > like? > Are they a type that has significant hysteresis? > > Bob > > > On Feb 23, 2020, at 3:05 PM, Jan-Derk Bakker via time-nuts > > <time-nuts@lists.febo.com <mailto:time-nuts@lists.febo.com>> wrote: > > > > Dear Attila, > > > > Thanks for the heads up. > > > > I am currently using a HPF both in hardware (capacitive coupling into the > > balun driving the ADC inputs) and in software before the ZCD. This should > > counteract the first-order effects of this offset, although second-order > > effects (converter nonlinearity et al) will of course still be an issue. > > The plots you've quoted include (different kinds of) DC offset correction > > for all but the "unfiltered" data; getting an efficient DC offset > > correction working in real time on this 8-bit platform was indeed one of > > the main challenges of the software-only approach. > > > > The FPGA daughterboard is currently in production at Eurocircuits; I hope > > to have time to work on those the coming month. I'll also try to book some > > time in our climate chamber. (I've had one of our GPSDO-designs running in > > our general labs since before Christmas; surrounding it with bottles of > > water works well enough to low pass filter temperature swings, but I still > > see 6 degrees C swings overnight as out HVAC only runs during business > > hours.) > > > > To be continued, > > > > JDB. > > > > On Sun, Feb 23, 2020 at 8:11 PM Attila Kinali via time-nuts < > > time-nuts@lists.febo.com <mailto:time-nuts@lists.febo.com>> wrote: > > > >> Good evening! > >> > >> I'm going through some old stuff... > >> > >> > >> On Wed, 27 Nov 2019 00:29:19 +0100 > >> Jan-Derk Bakker <jdbak...@gmail.com <mailto:jdbak...@gmail.com>> wrote: > >> > >>> This has yielded a combined "simple" signal > >>> processing path of a differentiator, a double comb filter and the offset > >>> estimator, which is getting very close in performance to the "ideal" band > >>> pass filter (OADEV of 3.77e-13@tau=1s versus 3.25e-13@tau=1s for the > >> BPF; > >>> full plot: > >>> > >> http://www.lartmaker.nl/time-nuts/DMTD%20self-noise%20OADEV%20with%20PLL%20and%20various%20filters.pdf > >> > >> <http://www.lartmaker.nl/time-nuts/DMTD%20self-noise%20OADEV%20with%20PLL%20and%20various%20filters.pdf> > >>> for this 600000-second recording: > >>> > >> http://www.lartmaker.nl/time-nuts/600ksec%20run%20with%20PLL,%2010811%20through%20splitter.png > >> > >> <http://www.lartmaker.nl/time-nuts/600ksec%20run%20with%20PLL,%2010811%20through%20splitter.png> > >>> . OADEV past ~1000sec is severely compromised by the fact that the > >>> measurement setup is in my home lab which sees temperature swings of up > >> to > >>> 20 degrees C and which does get bumped from time to time. Longer runs in > >> a > >>> more controlled setting forthcoming). > >> > >> > >> I can offer an explanation for the large effect of the zero correction seen > >> here. The LTC2140 is specified to have a +/-10µV/°C drift (at 1Vpp > >> setting). > >> Converted into phase error due to zero crossing shift, this turns into > >> a phase shift of +/-1ps/°C @ 10MHz. Note, the shift is given as +/- and > >> per channel, which means, it could very well be that the channels are > >> not matched in their temperature characteristics and thus the total phase > >> shift could be +/-2ps/°C ... though total shift being closer to 0.5ps/°C is > >> more likely. > >> > >> Summa sumarum: DC offset correction is important if a zero crossing > >> detector is used. > >> > >> Attila Kinali > >> > >> -- > >> <JaberWorky> The bad part of Zurich is where the degenerates > >> throw DARK chocolate at you. > >> > >> _______________________________________________ > >> time-nuts mailing list -- time-nuts@lists.febo.com > >> <mailto:time-nuts@lists.febo.com> > >> To unsubscribe, go to > >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > >> <http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com> > >> and follow the instructions there. > >> > > _______________________________________________ > > time-nuts mailing list -- time-nuts@lists.febo.com > > <mailto:time-nuts@lists.febo.com> > > To unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > <http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com> > > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
