[time-nuts] sine to square wave converter

Ed Palmer ed_palmer at sasktel.net
Thu Jul 10 16:17:12 EDT 2014


How much of an improvement does the LTC6957 give over, say, a simple 
74AC gate?

Actually, is there a list of different techniques and the performance of 
each?  I know that the LPRO Integration manual gives some good info for 
phase noise, but I'm not aware of a similar document for slew rate (AKA 
rise time).

Ed

On 7/10/2014 12:40 PM, bruce at ko4bb.com wrote:
>> On July 10, 2014 at 10:55 AM 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?
>> Thanks Bert Kehren
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> Although  CERN likes that circuit for its ruggedness and versatility its a
> little noisier than some alternative circuits.
>
> Currently Linear Technology's sine to square wave devices with selectable
> filtering (LTC6957 series) are better in that they are a closer approximation to
> the ideal zero crossing detector.
> Failing that the next best is perhaps an AC coupled  (both at input and between
> emitters) differential pair of 2N3906's or similar.
>
> Bruce



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