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OPA365: How to calculate the noise of two-stage operational amplifier

Part Number: OPA365

Hi,

I'd like to know how to calculate the two-stage OP amp's noise voltage.

Whether it is accurate that add up each stage's noise voltage.

Thanks.

  • Hi Eric,

    yes, if you keep in mind that the noise of stage 1 is amplified by stage 2 and that noise is added geometrically (sum over the squares...).

    It turns out that when choosing a high gain in the first stage, the noise of the following stages can become negligible. For instance: SQRT ( 1^2 + 0.3^2) = 1.04 which equals an increase of noise of only 0.3dB :-)

    Can you post a schematic with concrete component values?

    Kai

  • Well Eric, this comes up a lot, here was an example article talking about these issues,