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Design >> Mixed-Signal Design >> using offset to move idle tones in audio delta-sigma modulators
https://designers-guide.org/forum/YaBB.pl?num=1218189706

Message started by vivkr on Aug 8^th, 2008, 3:01am

Title: using offset to move idle tones in audio delta-sigma modulators
Post by vivkr on Aug 8^th, 2008, 3:01am

Hi All,

I would like to know if there is a generic method for predicting the tone location based on the offset level at input for a delta-sigma modulator.

I remember having read somewhere a formula like: f_tone = (offset/fullscale_voltage)*f_clk

However, I don't remember where and so I am not sure what assumptions led up to this equation, and if it is really valid, and for an arbitrary delta-sigma modulator.

Any comments would be appreciated.

Vivek

Title: Re: using offset to move idle tones in audio delta-sigma modulators
Post by thechopper on Aug 8^th, 2008, 7:45am

Hi Vivek,

I remember the modulator output (binary quantizer, +/-1 levels) for a dc input will generate tones located at:

lx' + k

where x'=(x-Y')/Δ; Y' being the adjacent quantization level to x and Δ the quantizer step size and with l and k being integers.

Further details can be found in "Oversampling methodsfor A/Dand D/A conversion"J. Candy & G.Temes, but unfortunately I do not recall the date for this reference.

See also " Spectral analysis of quantization noise in a single loop sigma delta modulator with dc input" R.M. Gray IEEE. Tran Comm. Jun 1989

Hope this helps
Regards

Tosei

Title: Re: using offset to move idle tones in audio delta-sigma modulators
Post by vivkr on Aug 12^th, 2008, 1:02am

Hi Tosei,

Thanks a lot. I will also check the references you mention.

Regards
Vivek