[time-nuts] sine to square wave converter

Magnus Danielson magnus at rubidium.dyndns.org
Thu Jul 10 17:13:30 EDT 2014


Bert,

Hard to predict without looking at the details. The main battle for a 
sine-to-square is to fight white and flicker phase noise as well as 
additive repetitive signals such as 50 Hz power noise creeping into the 
jitter. At the same time we try to get the conversion more long-term 
stable, so that temperature and voltage changes has less impact on the 
comparator point as it will convert voltage shifts into phase-shifts. 
However, as any active device, it too will add noise and phase-shifts.
I think that this is a field where you need to experiment and learn, and 
I try to show some alternative routes and some known traps which may 
solve one problem but cause another.

So, properly built, they should contribute if this is where you are 
having troubles, if it's not, they will add to long term ADEV for sure.

Cheers,
Magnus


On 07/10/2014 09:51 PM, EWKehren at aol.com wrote:
> Will the added stage negatively effect ADEV?
> Bert
>
>
> In a message dated 7/10/2014 3:48:44 P.M. Eastern Daylight Time,
> magnus at rubidium.dyndns.org writes:
>
> Bert,
>
> OK, good that you are familiar with it, it was not  obvious in that message.
>
> If you consider it as the first stage, and  that you then can put another
> (faster) stage after it until you go for  comparator. It's just the same
> thing as the multistage for beat-note, but  you run at a higher
> frequency. That way you should increase your slew-rate  step-wise.
>
> Cheers,
> Magnus
>
> On 07/10/2014 09:37 PM,  EWKehren at aol.com wrote:
>> Magnus
>> Thank you for your  recommendation I use Wenzel extensively as a matter of
>> fact I just  completed in the last three days two boards that have Wenzel
> on
>>   it  and in my projects I can count 14 boards. Rise and fall time is  my
>> concern but I  am open to suggestions that is why I turned to  the list
> looking
>> for the  best.
>> Thanks again    Bert Kehren
>>
>>
>> In a message dated 7/10/2014 3:09:52 P.M.  Eastern Daylight Time,
>> magnus at rubidium.dyndns.org  writes:
>>
>> Bert,
>>
>> On  07/10/2014 04:55 PM,  EWKehren at aol.com wrote:
>>> As part of the FE 405 B  project a  separate output circuit is in the
>> works.
>>> The  universal  controller and auxiliary board are the same as used in
> the
>>>    FE5680A  GPSDO but because of the very low  ADEV a separate circuit
> board
>>    that
>>> divides  by  three and has also two ground isolated  transformer  outputs
>> is in
>>> the works.The  question is what is  the  best sine to square wave
> converter
>>> with the lowest  ADEV   contribution. I am looking at Bruce's circuit
>> using  the
>>> ADCMP600. Any  other  ideas?
>>
>> Do look  at the Wenzel clockshaper [1], look at the  TADD-2 [2] schematic.
>>   It's a PNP long-tail pair. The strategy is to  provide modest gain.  A
>> known strategy to reduce 1/f noise and to some  degree  thermal
>> differences is naturally feedback, as you will find in  the  NIST papers.
>> Once you have the slew-rate up, going in for  the kill with a  straight
>> comparator should give you all the nice  output slew-rate you can  wish
> for.
>>
>> Thus, this is not all  that different to the mixer-setup you  have done.
>>
>> I have  modified my TADD-2 such that one of the output  channels is fed
>>   from the input circuit, and this provides me with a  squared up  version.
>> For a counter such as DTS-2070C, the difference is   significant, which
>> helps to show the potential of this simple   design.
>>
>> I think the basic approach can be improved, and how  far one has  to go
>> depends on how "clean" source you have. You  end up with interesting
>> measurement problems.
>>
>> An  indirect way to measure the goodness of a  squarer is to insert  some
>> known sine disturbance at say 30 or 40 dB below  the signal.  A straight
>> comparator won't work very well. Be careful with   selectivity of LC, as
>> it is a nice way to become temperature  dependent, so  low-Q solutions is
>> needed.
>>
>>   Cheers,
>> Magnus
>>
>> [1]   http://www.wenzel.com/documents/waveform.html
>> [2]   https://www.tapr.org/kits_tadd-2.html
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