op amp voltage follower

Discussion in 'Homework Help' started by athulascc, Apr 21, 2015.

  1. athulascc

    Thread Starter Member

    Aug 15, 2014
    86
    1
    IMG20150416WA0047.jpg

    in 2nd problem I can mark A0 , Rin and R0 with help of this model of op amp
    [​IMG]

    but what are others?

    are there any advance model?
     
  2. WBahn

    Moderator

    Mar 31, 2012
    17,748
    4,796
    You need to consider what each of those parameters means and then, with that understanding, determine how you would model it in the circuit.
     
  3. athulascc

    Thread Starter Member

    Aug 15, 2014
    86
    1
    yes. I do not know what are Ios and V0s
    also how to add Ib ? it is just current (biasing current) so how to model it?
     
  4. WBahn

    Moderator

    Mar 31, 2012
    17,748
    4,796
    Then it would seem like it is time to actually read the course material regarding non-ideal opamp parameters, wouldn't it?
     
  5. athulascc

    Thread Starter Member

    Aug 15, 2014
    86
    1
    I got it IMG_20150422_114138.jpg
     
  6. MrAl

    Well-Known Member

    Jun 17, 2014
    2,438
    492
    Hello,

    Since others here were nice enough to provide me with better images in times when i couldnt read the originals, i thought i would return the favor and clean up this image and rotate it so it is easier to view. Here is the enhanced image.

    So what were your answers for the questions then?
     
    Sinus23 likes this.
  7. kdillinger

    Active Member

    Jul 26, 2009
    141
    3
    Ios is input offset current and is the difference between the input bias current from each pin. Stated another way, each input pin will have a bias current: IB+ and IB-. These are both measured and the difference between them is the Input Offset Current.

    Vos is the input offset voltage and it is the voltage required at the inputs to ensure the output voltage of the op-amp is 0V.

    If you want to model Ib, you simply add an ideal current source on each input to circuit ground. To include Vos, you add a voltage source on the IN+ pin to circuit ground.

    A really good site that explains how to build a SPICE model from an op-amp datasheet is here:

    http://masteringelectronicsdesign.com/build-an-op-amp-spice-model-from-its-datasheet-part-4/

    There are 4 parts, I posted the link to part 4. You will see that input bias current, input bias current, and input offset voltage are modeled.
     
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