Hi Gianmarco,
I understand that you working on a Sigma-Delta DPWM. As stated in the question, you have used periodogram on the output square wave, yet it renders bad results. As per my understanding, you can leverage the fft function to compute the Fourier transform of the square wave and then calculate the power spectral density from the Fourier coefficients.
I have assumed a random data to discuss the workaround. Here is the code snippet for you reference
t = 0:(1/samplingRate):(duration-1/samplingRate);
squareWave = square(2*pi*frequency*t);
f = samplingRate*(0:(N/2))/N;
plot(f, 10*log10(psd(1:N/2+1)));
xlabel('Frequency (Hz)');
ylabel('Power Spectral Density (dB/Hz)');
title('Periodogram of Square Wave');
I believe that, following this approach would be helpful in supressing the errors and acheiving a satisfactory result for the periodogram of the square wave.
Have a look at the documentation page for fft function for better understanding
I hope this helps.
