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Difference between Noise Gain and ZI compensation in Non-Inverting circut?

Sonmer Wang
Prodigy 20 points

Hi,

In Fig. 8.31 in Tim Green's book, I change the connection of Cn left side to ground, just like use the Zn network as a ZI compensation.

And I can get the same "Modified Aol and 1/beta" figure with the initial one, using the same calculating formula.

But when I check the closed loop AC response, I get two different figure. The changed one has a bulge at mid frequency.

I know it's because of the change of Zn at mid frequency. But how can I predict this from the "Modified Aol and 1/beta" figure?

Could anyone help me ? Thanks a lot!

  • 0
    TI__Expert 6275 points

    Stability for Op Amps Part 8.pdfSee attached Part 8 of a previous article series.  Note the closed loop transfer will be different for inverting and non-inverting unless in non-inverting you tie input noise gain R-C circuit between +input and -input of op amp.  This is detailed in attached starting on page 18.

  • 0 in reply to Tim Green1
    Prodigy 20 points

    Hi Tim,

    Glad to see your reply!

    In fact my question is from my study of your book, <Operational Amplifier Stability>. Thanks for this book.

    My question is that, the two circuit have the same "modified Aol and 1/beta" curve, but why they have different close loop response? How can I predict this difference from the "modified Aol and 1/beta" curve?

    One circuit is Fig. 8.31 from your book, and the other is to change the left side of Cn from the middle point of R1 and R2 to Ground.

    Thanks!