Buttersworth low-pass filter Past Exam Question

Discussion in 'Homework Help' started by bogmonster1, Aug 6, 2010.

  1. bogmonster1

    Thread Starter New Member

    Aug 4, 2010
    Hi, I have a repeat in less than a month and could do with some help with this question from a past exam paper. Any help would be greatly appreciated.

    The required order N of a low-pass Butterworth filter, with a 3dB frequency of 1 r/s, such that the attenuation at the reject frequency wr is ≤ α (dB) can be obtained using
    N ≥ log(10α/10-1)/2log(wr)
    Determine the order and transfer function, using Table 1, of a Butterworth low-pass filter with a 3 dB cut-off frequency of 100kHz and a minimum attenuation of 20dB at 200kHz.
    Determine the unit step response of the filter.
    Hence calculate the filter overshoot.

    Heres Table 1 given:
    Order(N) : Factors
    2 : (s2+√2s+1)
    3 : (s+1)(s2+s+1)
    4 : (s2+1.84776s+1)(s2+0.76537s+1)
    5 : (s+1)(s2+0.6180s+1)(s2+1.6180s+1)
    6 : (s2+1.9378s+1)(s2+1.4142s+1)(s2+0.5176s+1)

    I am sorry if the table isn't easy to read.
  2. XIA

    New Member

    Aug 6, 2010
    hey bog
    though am not experienced but
    why dont you use MATLAB to solve it...?