Hi All,

We have designed an auto zero comparator for our project. I understand that the main purpose of auto zero comparator is to cancel small offset voltage. We are concerned about process variation too in our project. So I have a question regarding that. Is an auto zero comparator process variation sensitive ?

Regards,
Kanu

Hi AnalogDE,

Thanks for your reply. I wanted to confirm one more thing. It becomes insensitive to process variation...as the voltage on the capacitor is the voltage difference obtained due to process variation and is fed back from the output during cancellation phase ? Is this what you mean by a careful design.. ie, to sense the voltage at capacitor ?

Thanks,
Kanu

You cannot completely remove process sensitivity, but you can make those error sources "small enough" with proper design.

If you are cancelling at the input (input offset sampling or IOS scheme) then you need high enough gain so you are not affected by gain error.  You also need closed loop stability.

If you are cancelling at the output (output offset sampling or OOS scheme) you'll need a low gain amp so when it's sampling its offset it doesn't rail out.  The amp operates in open loop during sampling, so no worries about closed loop stability.

Look up Razavi's book "Principles of Data Conversion System Design" for a good introductory discussion of the above schemes.