Who can help about noise shaping of SDM?

cwcgo

Who can help about noise shaping of Sigma-Delta modulator?

As follow picture, it is noise shaping of MASH SDM.

MASH111 slop is similar MASH11 about -40dB/dec.

But it is correct for SDM output range.

I don't know where something is wrong.

Who can give me some suggestion?

Thank you very much.

cwcgo

It is Matlab source code:
===========================================================
close all;
clear all;

sim('NoiseShaping');

%Output stored by 'To Workspace' element
y3=fft(o3(:,1).*blackman(length(o3(:,1))),N)/length(o3(:,1)); %MASH111
y2=fft(o2(:,1).*blackman(length(o2(:,1))),N)/length(o2(:,1)); %MASH11
y1=fft(o1(:,1).*blackman(length(o1(:,1))),N)/length(o1(:,1)); %MASH1

Fs=1/(o3(2,1)-o3(1,1));
x=Fs/2*linspace(0,1,N/2);



figure(2)
semilogx([0:N/2-1]/N*Fs,20*log10(abs(y3(1:N/2))),[0:N/2-1]/N*Fs,20*log10(abs(y2(1:N/2))),'g',[0:N/2-1]/N*Fs,20*log10(abs(y1(1:N/2))),'r');
legend('MASH111','MASH11','MASH1');

grid;
title('Single-Sided Amplitude Spectrum of y(t)')
xlabel('Frequency (Hz)'),ylabel('|Y(f)|')
===========================================================
Thanks