dither generation circuits

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amir81

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dither generation

hi all
i am searching for some circuits to generate a dither signal for a delta-sigma ADC. i saw a circuit that used some not in ladder form and then use the last output as the input(cmos mixed signal circuit design, by jacob baker; vol-2; page 99). but when i simulate it with hspice, it doesn't work. any idea?
is there any good reference about circuits (not blocks) of generating dither noise for ADCs?
thanks
 

art of electronics dithering

nobody knows any thing about dither ?
 

A good dither is not always a simple thing to do. If you want a tone-free 1st order sigma delta loop, applying right dither is a real art.
Second order modulator dithering is much easier. Third and higher orders are often sufficiently dithered by their device noise.
What kind of sigma-delta loop do you use?
 

thanks.
my modulator is second order dsm.
 

Look ofr the yellow sd book (Norsworthy, Schreier, Temes, ....). Chapter 3 deals with idle tones and dithering. If you use your sd for audio application, you have to know how to detect idle tones and than find a good dither generator. I prefer dynamic dithering.
 

Yeah, dynamic dithering is good enough for low-end audio or voice.
Otherwise, just apply a white noise with sufficiently large amplitude to quantizer. One example of digital white noise source is given in Horowitz and Hill, Art of Electronics.
For 2nd-order sdm you are going to lose 10-15db of SNR if you want good signal suitable for high-end audio.
 

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