Reza.mrk77
Newbie level 2
As you know, Sigma-Delta Modulator as the core of sigma-delta ADCs defines the total SNR. I am simulating a very simple code for first order delta-sigma modulator. According to text books, the SNR of the first order modulator is calculated from:
predictedSNR = 10*log10(sig_power) + 9.03*r - 10*log10((A^2)/12) - 10*log10((pi^2)/3) r is the OSR ratio (r = log2(fs/(2*fb))) and A is the amplitude of sinusoidal input.
This is my MATLAB code:
But the results are: SNR = 45.9814
predictedSNR =56.7738
what's wrong with my code?
predictedSNR = 10*log10(sig_power) + 9.03*r - 10*log10((A^2)/12) - 10*log10((pi^2)/3) r is the OSR ratio (r = log2(fs/(2*fb))) and A is the amplitude of sinusoidal input.
This is my MATLAB code:
Code:
%delta modulator FFT clear clc fs = 1280; fb = 10; A = 1; r = log2(fs/(2*fb)); t = 0:1/fs:1 - 1/fs; y(1) = 0; y(2) = 0; x = A*sin(2*pifbt); for N=2:1:fs x1(N) = x(N) - y(N-1); x2(N) = sum(x1); if x2(N) >= 0 y(N) = 1; else y(N) = -1; end end plot(abs(fft(y))/1280); y_fft = abs(fft(y))/1280; sig_power = 2*(y_fft(11)^2); noise_power = 2*sum(y_fft(1:10).^2); SNR = 10*log10(sig_power/noise_power)
predictedSNR = 10*log10(sig_power) + 9.03*r - 10*log10((A^2)/12) - 10*log10((pi^2)/3)But the results are: SNR = 45.9814
predictedSNR =56.7738
what's wrong with my code?