About the quantization of digital Sigma-Delta Modulator

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gaom9

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Hi,
I am learning the Sigma-Delta frequency-Synthesizer, and in this design, the Sigma-Delta modultor is often a digital modulator, such as the MASH and Singal-Loop structure.
I have a question about the quantization in digital Σ-Δ modulator, how to make it come true? In some papers, the signal bus is cut short to discard the LSBs, and keep the MSB, and it is shown that by this method, the signal can be quantized, why? Is there any papers about this method, please?
And also, what is the relationship between discard signal bits and the quantized level, if I want to make a 8 level quantization, how many bits of the signal should be discard?

Thank you!
Best regards!


A second-order Σ-Δ modulator is shown as the figure following:


 

please read the book <Understanding sigma delta convertor > charpter design sigma delta DA, It explains the problem you encountered in details.
 

    gaom9

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