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> 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> 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> 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 >>> for this 600000-second recording: >>> >> 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 >> To unsubscribe, go to >> 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. _______________________________________________ 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.