On Sun, 13 Nov 2016 11:03:31 -0500 Tim Shoppa <[email protected]> wrote:
> Some AD DDS app notes give examples of spurs and choosing nearby (but not > exactly on freq) numbers that are much less bad for spurs - or at least > that move the spurs outside the cleanup filters/loops. I don't know of a > general example or even code that does this in a general way. > > One paper I like on the subject is this: > http://ttcla.org/vsreinhardt/DDS%20spur%20reduction%20techniques.pdf A treatment of the topic that I found quite good is [1]. The spurs of DDS are very similar to those of delta-sigma modulators (a DDS is delta-sigma modulator with a non-linear output mapping) and as far as I have seen, there are more analysis on the spurs of DS-modulators than on DDS systems (for a good reference on DS-modulators see [2]). The DDS spur reduction systems all vere very similar to what has been done to DS-modulators, like using a second or third order DS-modulator instead of a simple phase accumulator and using more bits in the sin/cos output and then using a first or second order DS-modulator there. Attila Kinali [1] "Exact Analysis of DDS Spurs and SNR due to Phase Truncation and Arbitrary Phase-to-Amplitude Errors", by Torosyan and Wilson, 2005 http://tycho.usno.navy.mil/ptti/ptti2005/paper8.pdf [2] "Understanding Delta-Sigma Converters" by Schreier and Temes, 2005 -- Malek's Law: Any simple idea will be worded in the most complicated way. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
