The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> Mixed-Signal Design >> basic question on sigma delta ADC
https://designers-guide.org/forum/YaBB.pl?num=1237376988

Message started by manodipan on Mar 18^th, 2009, 4:49am

Title: basic question on sigma delta ADC
Post by manodipan on Mar 18^th, 2009, 4:49am

Hi all,
I am just trying to understand switched capacitor type sigma delta ADC....let us say for example we have input sinusoid of common mode=0.6V and amplitude=0.3V with supply 1.2V....now the integrator's o/p range also is suppose 0.3 to 0.9V..now the o/p is either 1.2V or 0V based on the logic and fedback ..here is my question what value of reference(1.2V and 0V or 0.9V and 0.3V) should be chosen for DAC where my input FS=0.6V from 0.3V to 0.9V....
thanks for your help....

Title: Re: basic question on sigma delta ADC
Post by subgold on Mar 18^th, 2009, 12:42pm

i think it depends on the modulator gain. in another word, the ratio of the capacitor value between the sample path and the feedback path from the dac.

Title: Re: basic question on sigma delta ADC
Post by manodipan on Mar 21^st, 2009, 2:18am

Hi ,
thanks for ur reply......i think considering the extreme voltages that circuit can operate as reference we have to get the coefficients and select the cap sizes...

Title: Re: basic question on sigma delta ADC
Post by cmos.analogvala on Apr 23^rd, 2009, 1:58am

I think DAC should be bipolar and VREFP should be 0.9 and VREFN should be 0.3. Am I correct ?

Title: Re: basic question on sigma delta ADC
Post by manodipan on Apr 23^rd, 2009, 6:54am

Hi ,
I think you are right ,otherwise opamp o/p goes outside it's operating range.....now problem is that we need to generate two extra voltage references Vrefp and Vrefm....