[time-nuts] Question about frequency counter testing
hmurray at megapathdsl.net
Thu Apr 26 15:28:05 EDT 2018
olegskydan at gmail.com said:
> The plots I showed were made with approx. 5*10^6 timestamps per second, so
> theoretically I should get approx. 4ps equivalent resolution (or 11+
> significant digits in one second).
Is there a term for what I think you are doing?
If I understand (big if), you are doing the digital version of magic
down-conversion with an A/D. I can't even think of the name for that.
If I have a bunch of digital samples and count the transitions I can conpute
a frequency. But I would get the same results if the input frequency was X
plus the sampling frequency. Or 2X. ... The digital stream is the beat
between the input and the sampling frequency.
That technique depends on having a low jitter clock. There should be some
good math in there, but I don't see it.
A related trick is getting the time from something that ticks slowly, like
the RTC/CMOS clocks on PCs. They only tick once per second, but you can get
the time with (much) higher resolution if you poll until it ticks.
Don't forget about metastability.
These are my opinions. I hate spam.
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