[time-nuts] Question about frequency counter testing

Oleg Skydan olegskydan at gmail.com
Fri Apr 27 14:21:59 EDT 2018


From: "Azelio Boriani" <azelio.boriani at gmail.com>
Sent: Friday, April 27, 2018 12:16 AM

> If your hardware is capable of capturing up to 10 millions of
> timestamps per second and calculating LR "on the fly", it is not a so
> simple hardware, unless you consider simple hardware a 5megagates
> Spartan3 (maybe more is needed). Moreover: if your clock is, say, at
> most in an FPGA, 300MHz, your timestamps will have a one-shot
> resolution of few nanoseconds.

There is no FPGA. If I would use FPGA I probably should be able to get more
resolution for one shoot measurements, cause there are some simple methods 
of interpolating signal inside FPGA (they do not require additional 
hardware).
They can increase resolution by 2..16 times easily. So even with 200MHz 
internal
FPGA clock it is possible to reach 1ns one shoot resolution or even better.

I will show details when the project will be at the finishing stage.

> Where have you found a detailed
> description of the CNT91 counting method? The only detailed
> description I have found is the CNT90 (not 91) service manual and it
> uses interpolators (page 4-13 of the service manual).

Sorry, I meant CNT-90, but I bet cnt90/cnt91 use the same technique. You
can use interpolator along with the math processing. This will result
in better resolution and/or you can use less memory and less processing 
power.
I choose not use one to simplify the hardware. 




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