Transfer function of an op amp

Discussion in 'Homework Help' started by Geotraker, Feb 24, 2014.

  1. Geotraker

    Thread Starter New Member

    May 9, 2013
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    0
    How to find the transfer function (or the gain) of the following circuit?
    Can we short circuit R2 since there cannot be any input current?
     
  2. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    If this is an ideal opamp no current will flow in R2 so I would say yes. However are you sure you have drawn this correct. As your drawing looks very simlar to a Sallen and Key filter section
    http://www.ti.com/lit/an/sloa024b/sloa024b.pdf
     
  3. LvW

    Active Member

    Jun 13, 2013
    674
    100
    Yes - I agree with t06afre.
    However, in case of a true Sallen-Key lowpass (with C2 shifted to the non-inv. opamp input) the resistor R2, of course, must NOT be cancelled.
     
  4. Geotraker

    Thread Starter New Member

    May 9, 2013
    2
    0
    Thank you all. The schematic was wrong. Here is the correct one and I was able to solve that.







    Solving procedure,
    Apply KCL at V1
    Apply KCL at V2
    Remove V1 from above two equations and find V2-----(A)
    Apply KCL at V3 and find V3----(B)
    Apply Golden rules V2=V3
    Make (A)=(B) and find (Vout/Vin) ratio from it.
     
  5. LvW

    Active Member

    Jun 13, 2013
    674
    100
    Fine - that`s exactly the way I would solve the problem.
     
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