What is the dithering for sigma delta?

[boeysue]

If using comb filter,there will be many harmonics after filtering.But if use simply halfband filter,there willn't exit. Is dithering important for non-comb system in sigma delta?thanks for answering...

 

[jiangwp]

The dither make the quantization noise white noise in SD.
It also make the dc signal busy signal to average the quantization noise.
It is very important for the SD.
It is high frequency signal . If u use the comb filter , the filter will not eliminate the componet of frequency which is not the zero amplitude.

 

[markty]

What is simply halfband filter? ideal filter?

thx

 

[boeysue]

I use ideal lowpass to do that.

 

[borodenkov]

There's smth wrong with your design. First of all, are you talking about signal harmonicsm or idle tones?

If you do not have harmonics at the output of the sigma-delta modulator (without any LP filter at all), you should not get harmonics after using comb filter if your filter designed correctly.

In my experience, dithering is not important if you have multibit quantizer (there's some theoretical explanation of it in the Yellow book)