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# [SOLVED][Moved]: Continuous Sigma Delta ADC coefficients (Schreier Tool Box)

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##### Member level 5
I am designing a 3rd order Continuous time ADC , with 1 MHz Bandwidth ,32 OSR and 3 level Comparator.

I have a question regarding the coefficient values.

I used the equation:
coefficient * fs = 1/(R*C)

However, since the coefficient has 3 or 4 points precision (for instance: coeff = 0.0805 )
Assuming So the points appeared in the Resistor values (or capacitor)..

For instance: simulating the system with the exact R & C values obtained ==> Max SQNR = 69 dB
However, for layout considerations , I think i'll not be able to get a resistor value with so many points precision ,, so i tried approximating the R values to the nearest integer, and the max SQNR dropped 10 dB!!!

How can i resolve this issue?

Re: Continuous Sigma Delta ADC coefficients (Schreier Tool Box)

I am designing a 3rd order Continuous time ADC , with 1 MHz Bandwidth ,32 OSR and 3 level Comparator.

I have a question regarding the coefficient values.

I used the equation:
coefficient * fs = 1/(R*C)

However, since the coefficient has 3 or 4 points precision (for instance: coeff = 0.0805 )
Assuming So the points appeared in the Resistor values (or capacitor)..

For instance: simulating the system with the exact R & C values obtained ==> Max SQNR = 69 dB
However, for layout considerations , I think i'll not be able to get a resistor value with so many points precision ,, so i tried approximating the R values to the nearest integer, and the max SQNR dropped 10 dB!!!

How can i resolve this issue?

I guess that much precision is not important for sigma delta adcs.......... thats the beauty of this architecture...

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