Help regarding SNR of CT sigma delta

[vrs007]

snr ct



That is the paper I am trying to implement,without the half-delay i.e z^(-1/2)...I donno why my SNR stays constant at around 27 dB...I have attached the CT simulink file and the code used to calculate SNR...can anyone please chk it...


**broken link removed**

clc;
out1=simout';
N=8192*4; 
fs=640e6; 
y=out1(1:N);
w=hann(N);
y_w=y.*w';
fft_y=fft(y_w);
fft_y(N/2+1:N)=[];
amp_y=(abs(fft_y)./N)*sqrt(2);
y_db=20*log10(amp_y);
f=0:fs/N:((fs/2)-fs/N);
figure(1),
plot(f,y_db);
figure(2),
plot(amp_y);
signal_bin=[778:780];
noise_bin=[1:777 781:1024];
s=norm(abs(fft_y(signal_bin)));
n=norm(abs(fft_y(noise_bin)));
sdb=20*log10(s);
ndb=20*log10(n);
snr=20*log10(s/n);
disp(snr);disp(sdb);disp(ndb);

The main problem is my fundamental signal freq...it is not at 0dB

Spectrum from paper...and my spectrum...pl chk the peak...its not 0 dB
**broken link removed**
**broken link removed**