Just a FYI, you don't have to use sine lookup tables. You can generate sine and cosine on the fly with a coordic. Perhaps not easy at RF speed, but very common in audio DSP.
-----Original Message----- From: Jim Lux <[email protected]> Sender: [email protected] Date: Mon, 20 Jun 2011 12:04:24 To: <[email protected]> Reply-To: Discussion of precise time and frequency measurement <[email protected]> Subject: Re: [time-nuts] DDS'ery 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 ? > Tons.. 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. _______________________________________________ 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. _______________________________________________ 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.
