[time-nuts] sine to square wave converter

EWKehren at aol.com EWKehren at aol.com
Thu Jul 10 15:37:14 EDT 2014


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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