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Digital FIR Filter Design

  1. Jun 2, 2009 #1
    I have a question which is to design a filter of the form:

    y(n) = a(0)x(n) + a(1)x(n-1) + a(2)x(n-2) to remove a narrowband disturbance with frequency f0 = 70Hz.
    The sampling frequency, fs is 280Hz.

    I've made an attempt at answering it, but don't think my result is correct:

    w0 = (2*pi)* (f0/fs) = pi/2

    I then calculate the zeros of the filter from the definition of w

    z1 = exp(i*(pi/2))[
    z2 = exp(-i*(pi/z))
    where i = sqrt(-1)

    The transfer function of the filter is therefore;

    Z2H(z) = (z - exp(i*(pi/2))[ )(z - exp(-i*(pi/z)) )

    When expanded and simplified this gives

    H(z) = z2 + 1, so the filter function

    y(n) = x(n) + x(n - 2),
    giving
    a(0) = 1
    a(1) = 0
    a(2) = 1

    Which I'm pretty sure is wrong. Can anyone tell me where I have gone wrong?
     
  2. jcsd
  3. Dec 22, 2009 #2
    You did wrong while expanding and simplifying
     
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