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Op-Amp Current Gain with current source

  1. Mar 5, 2014 #1

    Maylis

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    1. The problem statement, all variables and given/known data
    Problem #6 on the attachment


    2. Relevant equations



    3. The attempt at a solution
    I am stuck because if I do KCL at the node above the current source, It seems like all of the current should go back into Rs and none from the current source goes up to Rf
     

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    Last edited: Mar 5, 2014
  2. jcsd
  3. Mar 5, 2014 #2

    CWatters

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    You forgot the attachment but I found it on another thread.

    The current through Rf is typically written as (Vo-Vi)/Rf.
     
  4. Mar 5, 2014 #3

    rude man

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    There are two sources of current into Rs, not just one!

    EDIT: donpacino is right. No current into Rs.
     
    Last edited: Mar 5, 2014
  5. Mar 5, 2014 #4

    donpacino

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    you want iL/is

    with negative feedback, the positive and negative nodes of the op-amp should equal each other. so the negative node=0V

    since the voltage at the negative node is zero, with an ideal steady state op-amp no current can flow through Rs.

    so the current through rf is Is.

    Use that to get you started
     
  6. Mar 5, 2014 #5

    Maylis

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    I have it solved, thank you!

    I got G = -Rf/RL
     
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