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Homework Help: Frequency Response of Op amp Circuits

  1. Jul 16, 2013 #1
    1. The problem statement, all variables and given/known data
    For this problem, the diagram of the circuit is attached. It was assigned to find the frequency response function of the circuit.

    2. Relevant equations
    E_o/E_i= -Zf/Zi

    3. The attempt at a solution
    I know for the top branch of the circuit, it has a negative feedback loop so therefore its:
    E_o/E_i = -Rf/Rin

    The problem I am having is with the resistor connected to the non inverting input. Since it doesn't have a loop structure, I question what it's output is and how to account for that in my frequency response function. The only examples I have found are of differential amplifiers. However those have two resistors that end up being connected to ground. Any assistance is appreciated.

    Attached Files:

    Last edited by a moderator: Jul 16, 2013
  2. jcsd
  3. Jul 16, 2013 #2


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    Staff: Mentor

    Welcome to the PF.

    The resistor at the + input is just there to help balance out the parasitic input offset voltage due to the input bias currents. It is often omitted with CMOS opamps, since their input bias currents are so small. The value of the resistor at the + input is often the parallel combination of the Ri and Rf resistors.

    So you should be able to ignore the resistor at the + input, IMO, for the purposes of calculating the frequency response of this circuit. Given that, how will you go about calculating the frequency response of this opamp circuit?
  4. Jul 17, 2013 #3


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    Science Advisor
    Homework Helper
    Gold Member

    How much info were you given about the opamp itself?
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