jimlux at earthlink.net
Mon Jun 20 19:04:24 UTC 2011
On 6/20/11 9:46 AM, Luis Cupido wrote:
> Gracias, Javier.
> As you read in my previous email I'm basically
> worried about close-in spurs (those that
> will pass through the PLL loop filter).
> will digest that 4th section... tks.
> Since I'm inside an FPGA... I'm eager to get
> spurs down without leaving the digital world...
> Anyone knows any literature covering that ?
Jouko Vankka wrote whole books about it.
Direct Digital Synthesizers and transmitters for software radio
Direct Digital Synthesizers: Theory, Design and Applications
You might want to look at various Error Feedback/Error Filtering schemes
which allow you to use a smaller cosine table and/or smaller DAC and
have better spur performance.
Vankka, J, "A direct digital synthesizer with a tunable error feedback
structure", IEEE Trans on Comm, V45, #4, pp416-420, 1997
Vankka's EF technique works quite well at suppressing spurs close to the
carrier (at the expense of pushing them farther out).
Reinhardt, V, "Spur Reduction Techniques in Direct Digital
Synthesizers", Proc Intl Freq Control Symp, 1993
Flanagan, M., Zimmerman, G., "Spur-reduced digital sinusoid synthesis"
IEEE Trans on Comm, V43, #7, pp2254-2262, 1995
(this one is about using dither to spread the spurs out)
O'Leary, P., Maloberti, F., "A direct-digital synthesizer with improved
spectral performance", IEEE Trans on Comm, V39, #7, 1991
You might also look at some of the spur cancellation things, such as the
one implemented in some of AD's DDS parts.. Basically, it's a second NCO
that generates a coherent signal that is subtracted/added to the primary
signal to "notch" out the spur.
More information about the time-nuts