Hi You could also say that with a longer accumulator, you get a closer approximation to a desired waveform.
If you compare the data sheets, the spur levels on the 48 bit parts ad9854.html <https://www.analog.com/en/products/ad9854.html> ad9912.html <https://www.analog.com/en/products/ad9912.html> https://www.analog.com/en/products/ad9956.html <https://www.analog.com/en/products/ad9956.html> are more related to the age of the part than the width when compared to the smaller parts https://www.analog.com/en/products/ad5930.html <https://www.analog.com/en/products/ad5930.html> https://www.analog.com/en/products/ad9834.html <https://www.analog.com/en/products/ad9834.html> Indeed, if you go through the entire page if parts https://www.analog.com/en/parametricsearch/11018#/ <https://www.analog.com/en/parametricsearch/11018#/> There does not appear to be a spur penalty for wider parts. Newer is indeed better, pretty much across the board. Bob > On Oct 7, 2020, at 8:58 PM, Mike Feher <mfe...@eozinc.com> wrote: > > It seems to me that now since the register so much longer, yet the D/A is the > same, updates to the D/A will take longer and therefore creating more close > in spurs. That 20logN does suck, but is real. I may suggest running the > output of the DDS through a 5 MHz crystal, or better yet a very narrow > crystal filter. 73 - Mike > > Mike B. Feher, N4FS > 89 Arnold Blvd. > Howell NJ 07731 > 848-245-9115 > > -----Original Message----- > From: time-nuts <time-nuts-boun...@lists.febo.com> On Behalf Of Bob kb8tq > Sent: Wednesday, October 7, 2020 7:34 PM > To: Discussion of precise time and frequency measurement > <time-nuts@lists.febo.com> > Cc: hmur...@megapathdsl.net > Subject: Re: [time-nuts] Aging 5065A ? > > Hi > > Well….. the existing synth in the 5065 is no champion spur wise. Coming up > with a DDS that is “as good as” is not all that crazy. > > The 5 MHz reference is multiplied to 6.x GHz and then mixed with the synth. > The close in phase noise of the multiplied signal is mixed with the synth. > The output is the sum of the two. > Going from 5 MHz to 6.x GHz gets you 20 log (N) … a bit over 60 db added > phase noise. > > The synth (at 100 ti 300 Hz offset) needs to be 60 db worse than the noise on > the 5 MHz before it even gets in the game. That’s not a really tough spec to > meet. > > Bob > w the instructions there. > > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
