[time-nuts] DDS'ery

lists at lazygranch.com lists at lazygranch.com
Mon Jun 20 19:17:35 UTC 2011

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 <jimlux at earthlink.net>
Sender: time-nuts-bounces at febo.com
Date: Mon, 20 Jun 2011 12:04:24 
To: <time-nuts at febo.com>
Reply-To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
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 ?

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.

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