The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> Mixed-Signal Design >> Noise budget in sigma-delta modulator
https://designers-guide.org/forum/YaBB.pl?num=1305562309

Message started by matteo.tonelli on May 16^th, 2011, 9:11am

Title: Noise budget in sigma-delta modulator
Post by matteo.tonelli on May 16^th, 2011, 9:11am

Hi,

Starting from the sigma-delta modulator parameters (sampling frequency, oversampling ratio and resolution) what's the noise budget to be considered for the operational amplifier, capacitors and reference voltages design?

Once the maximum noise power specs have been individuated, what's the integration bandwidth to be used in the blocks verification by simulation?

(starting from the power spectral density and calculating the noise power by integration).

In example:
Assuming the max op. amp. noise power to be vnmax^2, what's the integration bandwidth to evaluate the actual noise power vn^2 of the designed op. amp in order to verify vn^2 < vnmax^2?

Many thanks, Matteo

Title: Re: Noise budget in sigma-delta modulator
Post by jefkat on Jun 4^th, 2011, 8:48am

I would give about a half to the sampling caps and the rest to the amp and reference etc. The opamp power would be higher if you allocate too much to caps. On the other hand if the caps are not limiting the noise (and neither matching) then the amp would spend power driving these. so a tradeoff is somewhere in between. to begin with 1/2 is a good number.
The integration bandwidth is your signal bandwidth.
hope it helps