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Simulators >> Circuit Simulators >> Issues in SNR calculation for Delta Sigma ADC
https://designers-guide.org/forum/YaBB.pl?num=1345711869

Message started by sourav on Aug 23^rd, 2012, 1:50am

Title: Issues in SNR calculation for Delta Sigma ADC
Post by sourav on Aug 23^rd, 2012, 1:50am

Hi Guys,
I am finding issues in SNR calculation for my Simulink model and the model given in Screier toolbox.A pdf file is attached with the SNR figures and the model i have used

Specifications for my simulink model:

Amplitude= 0.8
Samples per period= 1170
Sample time= 10^-6
Frequency=2*pi*854.49 Hz

a,g,b,c have been calculated for CIFB model as:

H = synthesizeNTF(2,256,0,2);
[a,g,b,c] = realizeNTF(H,'CIFB')
a =
0.4721 1.2361
g =
0
b =
0.4721 1.2361 1.0000
c =
1 1

Matlab code for SNR calculation:
OSR = 256;
H = synthesizeNTF(2,OSR,0,2);
N = 8192; fB = ceil(N/(2*OSR));
f=7;
u = 0.8*sin(2*pi*f/N*[0:N-1]);
v = simulateDSM(u,H);
%%
t = 0:1000;
stairs(t, u(t+1),'g');
hold on;
stairs(t,v(t+1),'b');
axis([0 200 -1.2 1.2]);
ylabel('u, v');
%%
spec=fft(v.*ds_hann(N))/(N/4);
%figure
plot(linspace(0,0.5,N/2+1), ...
dbv(spec(1:N/2+1)));
axis([0 0.5 -120 0]);
grid on;
ylabel('dBFS/NBW')
snr=calculateSNR(spec(1:fB),f);
s=sprintf('SNR = %4.1fdB\n',snr)
text(0.25,-90,s);
s=sprintf('NBW=%7.5f',1.5/N);
text(0.25, -110, s);

Problem is that SNR for my model does'nt scale with OSR and also significantly smaller than theoretical one....

All sorts of suggestions are solicited....

Thanks and Regards,
Sourav