[time-nuts] sine to square wave converter

EWKehren at aol.com EWKehren at aol.com
Thu Jul 10 15:51:41 EDT 2014


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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