[time-nuts] A simple sampling DMTD

[Bob kb8tq]

Hi

Since most mixers also have DC offset issues, it is pretty common to high pass filter 
the signal before you try to hit a limiter.  Yes, this can bring in other issues, but the
net result is commonly a “win”. 

Bob


> On Feb 23, 2020, at 2:10 PM, Attila Kinali via time-nuts <time-nuts at 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 <jdbakker at 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 at tau=1s versus 3.25e-13 at 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.
> 
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