[time-nuts] sine to square wave circuits - performance data?
attila at kinali.ch
Wed Oct 4 16:49:29 UTC 2017
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 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.
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