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Design >> Mixed-Signal Design >> Why do we need CDS, not only use auto-zero instead?
https://designers-guide.org/forum/YaBB.pl?num=1519890134

Message started by Jacki on Feb 28^th, 2018, 11:42pm

Title: Why do we need CDS, not only use auto-zero instead?
Post by Jacki on Feb 28^th, 2018, 11:42pm

Hello,

Recently I recall the definition of correlated double sampling and auto-zeroing, i find it is not necessary to use CDS, we can just use auto-zeroing instead. Here we don't discuss the chopping.
For example, in the switched-capacitor amplifier, we can use capacitive reset instead of opamp reset to achieve the auto-zeroing. But if we want to use the CDS, we have to either add more capacitors or change the switching solution (for example the CDS integrator).
My first question is now that we can use auto-zeroing to achieve the offset cancellation, why we need CDS?
My second question is when we use CDS, the opamp should have lower thermal noise, why? If the CDS is normally used in oversampling, maybe it is better for the fast response at the output than auto-zeroing.
Any comments? Correction? Thank you very much.

Title: Re: Why do we need CDS, not only use auto-zero instead?
Post by Jacki on Mar 11^th, 2018, 5:26am

Can we say CDS is used for high-speed application compared with auto-zeroing?