[time-nuts] Programmable clock for BFO use....noise

Club-Internet Clemgill clemgill at club-internet.fr
Sat Sep 15 07:13:40 EDT 2018


Hi Attila, 
Very interesting, thanks.  
I found ref (2) by seems that need to pay or be to registered as a researcher to get ref (1). 
Is there a easier way to get a copy ? 
Thx,
Gilles. 

> Le 15 sept. 2018 à 12:26, Attila Kinali <attila at kinali.ch> a écrit :
> 
> On Fri, 14 Sep 2018 21:42:05 +0000
> Bryan _ <bpl521 at outlook.com> wrote:
> 
>> I would be interested in hearing more of the more suitable classes of
>> logic chips. I have a 20Mhz rubidium that I wanted to divide down to 10Mhz
> 
> Any logic family works, as long as it is fast enough to handle your
> input frequency. Due to the non-linear (aka digital) behaviour
> of a D-Flipflop style divider, it is recommended to use the slowest
> possible logic family for the task. Otherwise the harmonics of the
> switching of the FF will down-mix high frequency white noise down
> to the signal band (this is the reason for the 10*log(N) noise scaling
> of digital divider that Egan[1] and Calosso/Rubiola[2] and a few others 
> mentioned).
> 
> As a rule of thumb, I'd say that the FF should not be more than 10 to 20
> times faster than the input frequency, to limit noise down-mixing.
> If your FF is too fast or you want to reduce the noise floor, capacitively
> loading and/or having some additional resistance in the Vcc and GND lines
> will help slow it down. But ensure that the resistance is still low enough
> that the FF's supply stays within specs at all time. Similarly, the
> capacitive loading should be low enough that the output current is within
> reasonable bounds.
> 
> Alternatively, using the Λ-divider approach[2] and introducing voltage
> steps between 0 and 1 will also reduce down-mixing.
> 
> If you divide by something that is not a power of 2, then it is important
> that each stage produces an output waveform with a 50% duty cycle. Otherwise
> flicker noise which has been up-mixed by a previous stage, will be down-mixed
> into the signal band, increasing the close-in phase-noise.
> 
> 
> 			Attila Kinali
> 
> [1] "Modeling Phase Noise in Frequency Dividers," by Egan, 1990
> 
> [2] "The Sampling Theorem in Pi and Lambda Digital Frequency Dividers,"
> by Calosso and Rubiola 2013
> 
> -- 
> <JaberWorky>	The bad part of Zurich is where the degenerates
>                throw DARK chocolate at you.
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.




More information about the time-nuts mailing list