Calculating the transfer function for a active filter

Discussion in 'Homework Help' started by RigbyEl, May 5, 2010.

  1. RigbyEl

    Thread Starter New Member

    May 5, 2010
    1
    0
    Hi all,

    I'm in my first semester of EE and for this weeks tute questions I've been asked to calculate the formula for the frequency dependent complex, phasor transfer function for this circuit:

    [​IMG]

    I'm a bit stuck, the question sheet gives the hint of writing KCL equations at the Vx and V- nodes but that hasn't helped me too much yet. This is what I've tried to do:

    excuse the crappy drawing..

    [​IMG]

    [​IMG]

    I'm a bit lost of where to go from there though, was I supposed to have I(out) in the second KCL equation so that I'd be able to solve for Vin/Vout? How would I do this? My knowledge of OP amps is a bit sketchy, it wasn't taught that well.

    If I'm totally off (I suspect I might be!!) let me know.

    Thanks. :)
     
  2. kdillinger

    Active Member

    Jul 26, 2009
    141
    3
    Your equation at node Vx is wrong. Using KCL at node Vx:

    (Vin-Vx)/10kΩ - Vx(s*0.1uF) - Vx/10kΩ - (Vx-Vout)/10kΩ = 0

    That should help you.

    BTW, what you have is a multiple feedback lowpass filter.
     
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