Op Amp Open-Loop Gain and Open-Loop Gain Nonlinearity

I have seen the content of Mini Tutorial MT-044 appear as far back as 1999 on pages 3.7 - 3.10 of an AD publication entitled "Practical Design Techniques for Sensor Signal Conditioning", Walt Kester, ISBN-0-916550-20-6. In all instances the formula for open-gain nonlinearity is simply stated as being approximately (e.g. (6) in MT-044):

but there is never an explanation of how this formula was derived. What does this formula mean and how it is derived?

Also, Eq. 5 in MT-044 should read 100,001 * (dVX/dVy)

Thanks.

  • 0
    •  Analog Employees 
    on Oct 13, 2021 3:00 AM

    Hi Ross,

    Apologies for the late response. Kindly check the attached PPT for the discussion of the Mini Tutorial mentioned.

    PPTX

    Hope this helps!

    Best regards,

    Kristine

  • Hi Kristine,

    It was interesting to look at the presentation. I liked the hand-written notes!

    Tim did a nice job deriving e.q. (3) in the mini-tutorial. But that's not what is troubling me. Sorry, Tim!

    The issue is on slide 3, where the open-loop gain nonlinearity expression is introduced. But, as in Fig. 1 or e.q. (6) in MT-004, it is simply offered as fact. It's as if this is an obvious result. I am still not able to derive it.

    What makes sense to me is that the non-linearity error is (AVOL,max - AVOL,min)/(Ideal AVOL). But that does not take me far.