[time-nuts] An (unknown?) nasty feature of the DDS principle for time nuts applications

Brian Davis brimdavis at aol.com
Thu Jan 27 00:12:30 UTC 2011

I posted a link to some plots of phase and amplitude 
spurious "pileups" here a while back:

"  Even when not multiplied, the normal close in phase noise floor of
" the DDS can be masked by spurs and intermods near many tune words.
"  I put together some plots of this a few years back, modeling just the
" numerical spurs ( phase truncation and and amplitude quantization ) 
" _not_ the harmonically related intermods, near some 'pile-up' 
"  There are a few off-by-two errors in here that I need to fix, but
" the plots still illustrate the problem well ( put Acrobat in single
" page mode and mouse wheel scroll to 'animate' the plots ) :
"  http://fpgastuff.googlepages.com/dds_oddities.pdf

  Those plots were generated in the context of a discussion about the 
of these close in DDS spurious when used as the reference for a PLL:



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