Hi, All,

I have another difficult fundamental question for the first order delta sigma modulator.


                                                       ff
                                                       |
x -----(+) ----- {z^-1/(1-z^-1)} ------(+) ------> [8-bit ADC] ------> y
          |                                                                                |
           -----------------------------------------------------------------


The feedback is a negative one, with 8-bit ideal DAC.

The ADC is also a ideal one.

ff is white noise. x is a DC input.

According to the linear model, the TF is as:
y = x*z^-1 + (ff+qq) * (1-z^-1), where qq is the quantization noise.

According to this model, the ff will also be first-order shaped. Right?

However, from the Matlab behavioral model, ff is NOT shaped.

Is there anybody who can explain this well?

Thanks a lot.

I think your conclusion is wrong. The output y will contain ff and x. You basically consider the modulator open-loop.

When you close the loop you get y(n) = x(n-1) + (ff(n) - ff(n-1)).

How do you simulate this modulator?

Cheers