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Design >> Mixed-Signal Design >> Sigma delta modulator quantization noise problem
https://designers-guide.org/forum/YaBB.pl?num=1243412815

Message started by acezhy on May 27^th, 2009, 1:26am

Title: Sigma delta modulator quantization noise problem
Post by acezhy on May 27^th, 2009, 1:26am

Hi all,

The digital sigma delta modulator is a 3rd order mash 1-1-1 digital modulator and the output range is -3~4. The operation frequency is fs. What I care is the output noise magnitude at N*fs/2.
Firstly, I did a transient simulation and do FFT for the sdm output number. By observing the spectrum, the magnitude points at N*fs/2 in decibel has a -20dB/dec slope.
On the other hand, however, if I calculate the spectrum in frequency domain in Mathcad. The magnitude values at N*fs/2 have no difference.
Could anyone help me explain this? Did I miss something?

Thank you very much!
-Ryan

Title: Re: Sigma delta modulator quantization noise problem
Post by ywguo on Jun 16^th, 2009, 10:31pm

Hi Ryan,

Could you please give more info about your structure and simulation?

Modulator structure
Plot of FFT
Do you mean the output noise magnitude at N*fs/2 or fs/2? N*fs/2 is out of the nyquist bandwidth.
If yes, what is N?
...