The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> Analog Design >> Capacitive DAC Unit Cell Size in ADC
https://designers-guide.org/forum/YaBB.pl?num=1619589962

Message started by niloun on Apr 27^th, 2021, 11:06pm

Title: Capacitive DAC Unit Cell Size in ADC
Post by niloun on Apr 27^th, 2021, 11:06pm

Hi everyone,

When we want to calculate ADCs sampling capacitor size we choose C such that thermal noise level is less (or equal) than quantization noise

KT/C<Δ²/12

Which leads to

C>12KT×2^2b/V_FS²

My question is that if "C" here is the total capacitance of the capacitor array or unit cell capacitor? and why?

For example if in the case of an eight bit ADC we find C>20fF from C>12KT×2^2b/V_FS²
should we divide 20fF by 2⁸ to find the minimum unit cell size or C is the minimum unit cell size itself?

Title: Re: Capacitive DAC Unit Cell Size in ADC
Post by niloun on Mar 3^rd, 2022, 10:55am

Solved.
"C" here is the total capacitance of the capacitor array.

Thanks,
Nilou