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Homework Help: Design of differential amplifier

  1. Oct 9, 2008 #1
    1. The problem statement, all variables and given/known data


    2. Relevant equations

    According to my book, if R3 = R2 and R4 = R1, I can use the following formula:

    Vo = (R2/R1)(V2 - V1).

    3. The attempt at a solution

    We want R2/R1 to equal 5. This means that R3 and R2 must be 5*3,3 = 16.5 k(ohms).

    However, I don't know what to do with the inner resistance of V2 and Vo. Any suggestions?
  2. jcsd
  3. Oct 10, 2008 #2


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    Science Advisor
    Gold Member

    For an ideal op-amp, the input current is zero.
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