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Homework Help: Write transfer function G(s) of circuit

  1. Nov 27, 2009 #1
    1. The problem statement, all variables and given/known data

    The problem ask me to write the transfert function of a electrical circuit witch include an operational amplifier. I've follow some instruction bur I cannot figure out from this problem.
    Could you suggest me somethings?

    I'd like to calculate G(S) = U(s) / Y(s)

    where U(s) is Lasplace transform of u(t) and Y(s) is Lasplace transform of y(t)

    The circuit, and solution is in attached file tf.pdf.

    I start cualculating the equivalent impedance Z2.

    I get: R + 1/SC

    How can I write equivalent impedance for Z1.

    I'd like to apply the formula:

    G(s) = U(s)/Y(s) = -Z2/Z1

    Thank you very much!

    2. Relevant equations

    3. The attempt at a solution

    Attached Files:

    • tf.pdf
      File size:
      62.9 KB
  2. jcsd
  3. Nov 27, 2009 #2

    The Electrician

    User Avatar
    Gold Member

    Keeping in mind that the minus input of the opamp is a virtual ground, you should calculate how much current will flow to ground from the right end of the Z1 network if you apply 1 volt at the input node u. Then take the ratio of the applied voltage (1 volt) and the output current in the rightmost resistor R of the Z1 network, if the right end of that resistor is grounded.

    That ratio will be the equivalent impedance of the Z1 network.
  4. Nov 30, 2009 #3
    Re: Write transfer function G(s) of circuit - Solved

    Thank you for your answer. I've found that it's possible to solve this kind of problem in simple way applying: Y-Δ transform

    The link of a page on wikipedia is the following:

    I hope that someone could find this post helpful.

    Thank you
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