A Question About Calculating FFT in Delta Sigma Modulators

[naalald]

I wonder why we usually use three bins for the signal power when calculating FFT in delta sigma modulators? There should be just one frequency component that is the signal itself; But we use the signal frequency component, it's previous FFT component and it's next one. Why?

 

[lladnar23]

Remember that the output of a Delta-Sigma is typically not periodic, even if your input is. As a consequence, you won't be able to use coherent sampling (sample an integer number of cycles). When you generate your FFT, this will produce spectral leakage -- part of your signal will "spill over" into adjacent frequency bins. So by using the signal bin and also the two neighboring bins, you are accounting for all of the signal power.

 

[nozone]

seems we also need to apply windows while doing the fft, so that it have better match

 

[jiangxb]

Re: A Question About Calculating FFT in Delta Sigma Modulato

that is spectral leakage from the signal.
the point number that is added up to get the signal power depend on the used window. three points for hanning window.