dither generation circuits

[amir81]

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

 

[amir81]

art of electronics dithering

nobody knows any thing about dither ?

 

[steer]

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?

 

[amir81]

thanks.
my modulator is second order dsm.

 

[eda4you]

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.

 

[steer]

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.