sigma delta post processing in matlab (fft)

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fra2k10

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Hi, I am simulating a sigma delta modulator in spectre. I have chosen
fs=60kHz, fin=205 Hz, so that OSR is approximately 150 and so that coherent sampling condition is satisfied for N=2048, nper=7 (2OSR=N/nper).

I have run a tran simulation of 34.2 ms ( equal to nper periods) and I would like to post-process it in matlab for calculating the SNR through FFT.

The problem is that I have set the transient step = 0.2 us and I have a huge amount of output points (382000) describing the output bit stream.
How can I process them?

Thx,

Francis

Do not post the same message in different sections.....Mod Aya2002
 

you can down-sample your output: take one every 83 samples of your modulator output stream. Unfortunately, the ratio between the sample rate and your transient step is 83.3... so it won't be perfect.
 

Hi, thank you for your reply.
I am going on with my simulations but I am still having problem with the fft.
My SD ia a two bits architecture, with B0 to B3 as outputs.
How am I supposed to do the fft?
I mean that each of them is a high frequency signal and the combination of them represents the output. Which signal I should apply the fft then?
 

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