NEED HELP FOR OP-AMP IN BGR

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Before asking the question I would like to attach the image of the BGR regarding which I have some doubts.

From what I have read, due to the high gain of the op-amp, the two inputs of the op-amp "Va and Vb" are always at an equal potential such that the PTAT current flows across R1. But if the potential at the two inputs is equal then shouldn't the output of the opamp be 0 (or very close to it) as V0 = Av*(Vb- Va). I know this might be a silly question but it is haunting me for a few days.

Comments

D
No, the most important features of the op.amp are zero input offset and infinite open loop gain. The latter meaning that a trivial input difference, from zero, can swing the output to either "rail" (of course nonidealities prevent reaching the rail exactly, given any loading).
 
O
Hello,
I wonder effect of the opamp's finite gain & offset on the bandgap voltage in terms of temperature curve and absolute values.

According to following offset equation from "Banba" paper, offset voltage shifts only absolute values, not temperature coefficient unless offset depends on temperature. Is it correct?


Also, can we consider finite gain effect as offset effect?

Lastly, is opamp offset voltage temperature independent? How much vary with temperature?
 
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