[time-nuts] DDS spurs (was: Secondary phase noise standard & FE405)

[Attila Kinali]

On Sun, 13 Nov 2016 11:03:31 -0500
Tim Shoppa <tshoppa at gmail.com> 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

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