[time-nuts] sine to square wave circuits - performance data?

Bob kb8tq kb8tq at n1k.org
Wed Oct 4 16:47:22 EDT 2017


Hi

> On Oct 4, 2017, at 12:49 PM, Attila Kinali <attila at kinali.ch> wrote:
> 
> On Wed, 4 Oct 2017 11:01:31 -0400
> Bob kb8tq <kb8tq at n1k.org> wrote:
> 
>> This gets into the “other side” of the whole comparator / squaring circuit
>> test process. What matters for ADEV and what matters for phase noise at
>> 100KHz offset likely are not the same thing. A lot of circuits do quite well
>> inside 100 Hz, but not so well above that offset. 
> 
> Yes. Definitely something one should consider. 
> 
> For completeness:
> 
> * For cycle-to-cycle jitter what matters is the white noise floor.
>  Ie everything above 100Hz-1kHz, as this is the largest contributor
>  of "short" tau jitter. This is the component that limits e.g. the
>  single shot resolution of time-interval counters.
> 
> * For ADEV/TDEV at "long" taus >1-100s what matters is the close-in, 1/f^a,
>  flicker noise. As white noise averages out with sqrt(n), with n
>  being the number of samples taken, but 1/f^a noise does not.
> 
> When the transistion to from short to long taus happens depends as much
> on the noise as on the rate of measurement. If we measure a 1PPS, the
> the ADEV at tau=1s will be dominated by white noise and at tau=10s it
> could be still a significant portion of the noise seen. On the other
> hand, if we measure a 1kHz signal (at that rate), the tau=1s will be
> (most likely) dominated by the flicker noise.
> 
> 
>> Driving a 5V powered CMOS gate with 5.5V p-p does a pretty good job ….
> 
> If you have this much signal, yes. Not everyone has the luxury of an
> steady +19dBm input signal. Part of the reason why I am looking into
> this is because I wanted a squaring circuit that can work down to +2dBm,
> where, so I have been told, CMOS gates do not work well anymore.
> 

You don’t need 19 DBM to put 5.5V into a gate. A broadband transformer
or a matching network and 0 DBM will do just fine. Neither one is terribly
hard to come by. Neither one takes up much board space. 

Bob


> 
> 			Attila Kinali
> -- 
> It is upon moral qualities that a society is ultimately founded. All 
> the prosperity and technological sophistication in the world is of no 
> use without that foundation.
>                 -- Miss Matheson, The Diamond Age, Neil Stephenson
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