Derive transfer function for LP filter

Discussion in 'Homework Help' started by tblues87, Apr 9, 2013.

  1. tblues87

    Thread Starter New Member

    Apr 9, 2013

    can someone help me derive transfer function of low pass biquad 2nd order filter. The transfer function should be Vout/Vin but my problem is if all the positive inputs to the opAmps are grounded the Vout is then 0.

    Example, for the first amp
    V3 = A(V+ - V3)
    V3/A = V+ - V3
    lim(A) -inf
    V+ = V3
    if V+ is grounded then is 0 and V3 = 0.

  2. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    The fact that the + inputs are grounded does not imply that Vout is zero.

    You have 7 numbered nodes, so you will have to write at least 7 equations if you use nodal analysis. The transfer function will be very complicated.

    Do you really want to derive a complete transfer function in terms of the individual components, or will a generalized function as a ratio of a quadratic numerator and quadratic denominator be adequate?