Hello everyone, I am simulating a first order sigma delta ADC and having a problem with SNDR and ENOB. first I got fft through ngspice and transferred it to matlab and tried 10log(power main freq/summation of power) and I got nothing valid. Also I tried SINAD on the linearized & digitized output, still nothing. Is it a right way to perform moving average on the digitized output and then run SINAD? Thanks for your replies

Hi, so what are you not getting as "valid"???

Hi, dear Sumanto, thanks for your reply. I'm getting SNDR around zero but after running moving average it raises to around 50. Although that's not the point. I was wondering if my approach is right or not.

For SNR calculation, when integrating the noise of a Delta-Sigma output, make sure only the noise bins inside the signal band are integrated. If you are integrating all the noise bins from DC to fs/2, you won’t get the correct result.

Dear Robin, thank you for your reply. That totally makes sense I'll include the in-band noise then

Hi @Amirhossein zanjani please check if this helps https://sourceforge.net/p/ngspice/support-requests/35/

You’re welcome, good luck