second order Butterworth filter

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vinay
vinay on 27 May 2015
Answered: Star Strider on 27 May 2015
Can any one tell me how to plot the frequency response for the following digital second order Butterworth filter using MATLAB.
(1+2*z^-1+z^-2)/(10.2358-9.6464z^-1+3.4106).
This should be a low pass filter with cutoff at 1KHz. You can plot up to 8 KHz so that we can show the aliasing also
  1 Comment
Walter Roberson
Walter Roberson on 27 May 2015
Are you sure you want the denominator to have two coefficients that are independent of z? Are you sure that one of the two should not be followed by z^-2 ?

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Answers (1)

Star Strider
Star Strider on 27 May 2015
I would address Walter’s concerns about the missing z term, then convert it to a transfer function (vector) representation, and use the freqz function to create the Bode plot.
I don’t know what you mean by ‘show the aliasing also’ since to the best of my knowledge, you can only filter up to the Nyquist frequency with a properly-designed digital filter.
You cannot use a digital filter as an anti-aliasing filter. Anti-aliasing has to be done in hardware before the ADC.

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