[time-nuts] Re: pulling some crystals

[Jim Lux]

There are some Analog Devices datasheets and ap notes that talk about it.  There’s a book by Vankka
https://link.springer.com/book/10.1007/978-1-4757-3395-2
Look at some of the second generation DDSs. (I.e. the ones that came out after the AD985x series, which are straight DDS with phase accumulator - sin/cos- dac)

And a few papers, I’ll look for them.  - As for a generalized way to predict the spurs - I don’t think so, I think you have to model it for your case.  We talked about it on this list about 5-10 years ago.  We were looking into it to improve turnaround performance for deep space transponders, where you care a lot about close in phase noise because it affects performance for ranging. Not so much for low (~10 bps) data rates, since those are a subcarrier 10-20 kHz away.

Essentially, one technique is to predict the spur (e.g. from a table, or suitable arithmetic) and have another DDS that coherently subtracts it. Another is to put some sort of (digital) filtering in the path between the phase accumulator and the sin/cos lookup, or between the sin/cos lookup and the DAC. Â 




 


On Wed, 13 Dec 2023 01:47:50 -0800, Hal Murray via time-nuts <time-nuts at lists.febo.com> wrote:

Jim Lux said:
> This may or may not work, depending on your phase noise requirements.  There
> are techniques for DDSes to make the close in phase noise small (at the
> expense of raising it farther out - it's always like squishing a balloon).

Could you say more about hat area? Is there a good paper or chapter of a book?

Is there a simple formula for the size and offset of the closest spurs? Do
they ever get lost in the phase noise of the main peak?


--
These are my opinions. I hate spam.


_______________________________________________
time-nuts mailing list -- time-nuts at lists.febo.com
To unsubscribe send an email to time-nuts-leave at lists.febo.com
Â