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Design >> Mixed-Signal Design >> Sigma-Delta Mod: Spurious tone
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Message started by neoflash on Nov 17^th, 2007, 2:06am

Title: Sigma-Delta Mod: Spurious tone
Post by neoflash on Nov 17^th, 2007, 2:06am

In text book from Temes, 2nd order modulator suffer non-linearity from quantizer and thus contains tone in spectrum.

Why 1st order modulator does not suffer same problem and looks spur free?

Title: Re: Sigma-Delta Mod: Spurious tone
Post by Berti on Nov 18^th, 2007, 10:32pm

Hi Neoflash,

which text book are you referring to? Which chapter?

Because I think you are confusing different issues. I guess what you mean are idle tones, which might
be a problem in single-bit low-order (1st&2nd order) modulator.
Please post the full reference of the text book to clarify the question.

Regards

Title: Re: Sigma-Delta Mod: Spurious tone
Post by neoflash on Nov 19^th, 2007, 6:04am

Book named: Delta-Sigma Data Converters. by Temes and Schreier

In figure 3.6, we see MOD2 contains spurious tone which does not appear in fig2.20 for mod1.

Title: Re: Sigma-Delta Mod: Spurious tone
Post by Berti on Nov 20^th, 2007, 12:01am

Hi,

the name of the book is "UNDERSTANDING delta-sigma data converters". I think the difference is that in fig 3.6 the spectrum is shown using averaging
(uncorrelated noise is reduced and the tones are better visible), while in fig. 2.20 no averaging is used and it is therefore hard to distiguish
between noise and tones.

But in general a first-order modulator is worse than second-order in terms of tonal behavior.

Regards

Title: Re: Sigma-Delta Mod: Spurious tone
Post by neoflash on Nov 20^th, 2007, 5:45am

Oh, that's good to learn about it. Author emphasized tones in 2nd order MOD, so it is a bit confusing.

Thanks for this clarification.