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OPA211: The question for calculation Vos an IB

Part Number: OPA211

Hello,

I have a little question after I watch the "2.2 TI Precision Labs - Op Amps: Vos and Ib - Lab" video.

The page 4 show  the circuit contain two OPA211, but in page 6, why the formula of Vib only times the Req of first OPA211? Can we ignore the IB of second OP?

If we can't ignore the IB of second OP, why the circuit need secondary amplifier?

I am the beginner for design OP-amp circuit, and hope someone can answer this question,

Thanks.