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
    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:


    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..



    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
    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.