OPA2211A noise calculation on datasheet

Iven Xu

Intellectual 2090 points

Other Parts Discussed in Thread: OPA2211A

Hi,

I cannot understand the noise calculation of inverting gain configuration in page 16 and figure 47 of OPA2211A.

Why the current noise is just (In*Rs)², but not multiply the noise gain looks like as in non-inverting gain configuration?

Thanks and best regards!

Iven

over 11 years ago

0 Bruce Trump over 11 years ago

Guru 21975 points

Ivan,

This noise calculation shows the individual output noise contribution from each component in separate terms. Feedback forces current noise to flow only through R2 in contributing its output noise component. Assume that the op amp feedback holds 0V on the inverting input. The noise current cannot flow through R1. It must all flow through R2.

I hope this is clear and helps your understanding.

Regards, Bruce.

0 zhi zhang1 over 11 years ago in reply to Bruce Trump

Prodigy 10 points

It's very helpful. Thanks very much.

0 Iven Xu over 11 years ago in reply to Bruce Trump

TI__Intellectual 2090 points

Bruce,

Thanks for your explanation, I got it now!

Best regards, Iven.

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OPA2211A noise calculation on datasheet