This question refers to the link https://pure.tue.nl/ws/portalfiles/portal/1546321/521243.pdf. In chapter 4 it discusses the topic of dead zone, which appears in the delta sigma modulator. Dead zone means that when input signal to the modulator is very small than the output of the modulator will not follow the input, for small input signal the output of the modulator depends on the state of the modulator. The input must be higher than the dead zone to break the repetative pattern of the modulator.

The question: How the the dead zone is related to the filter order of the modulator? In the link it shows for first order filter but not much is written about higher order modulator and dead zone.


From the paper you link to:

Modulators with a higher order loop filter also exhibit a dead-zone which can be calculated in a similar manner. Because of the higher gain in the loop filter, the dead-zone of these modulators will be considerably smaller than the dead-zone of the first order SDM*. Very small signals (including system noise) will disturb the idle patterns of such SDMs, rendering the dead-zone undetectable in practical implementations.

And if you had a situation where system noise didn't disturb the idle patterns that cause dead zones, you could always inject some dither that's intentionally designed to have its spectral content at high frequencies.

* SDM = sigma delta modulator, in that paper's nomenclature.

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  • $\begingroup$ Thanks, did not see that comment. The problem is in my case dead zone seems to be higher with order. $\endgroup$ – Creator Dec 9 '19 at 22:24
  • $\begingroup$ I'm just guessing (I've only designed first-order sigma-delta modulators), but I would assume that a poorly designed higher-order modulator is worse than a first-order modulator. And before you ask -- no, I'm no expert; that's just based on gut feel. So -- check your modulator design, and maybe the implementation? If I were in charge and seeing this symptom a dumb software bug would have equal likelihood to a subtle problem in the modulator design. $\endgroup$ – TimWescott Dec 9 '19 at 22:29
  • $\begingroup$ I am using the modulator based on output filter impuse reaponse with LMI constraint given in the paper " Noise Weighting in the Design of Delta Sigma Modulators (With a Psychoacoustic Coder as an Example)" All aspects of the modulator are fine although the filter order is 49. Only dead zone is bit higher, trying to analyse what is going on. Thank you for your ressponse. $\endgroup$ – Creator Dec 9 '19 at 23:01

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