06 December 2007

IIR Filter

Frequency Response of a IIR Filter


Any IIR systems the transfer function H(z) is often expressed as a ratio of polynomials such as

H(ejw) = [ b0+ b1z-1+......+bn z-N / a0+a1z-1+...+amz-N ] |z=ejwt

The above equation is same as that of the general representation of z-transform. Therefore to find frequency response of IIR system we can make use of the command "freqz"


  1. Input the numerator coefficients
  2. Input the numerator coefficients
  3. Input the sampling frequency , fs
  4. Calculate the Nyquist frequency npt (npt = fs/2)
  5. Find the frequency response using "freqz" command


%Program to find frequency response of a given IIR response

b=input ('Enter the numerator coefficients ');

a=input (' Enter the denominator coefficients');

fs=input ('Enter the sampling frequency ');

npt=fs ./2 ; % number of frequency points

freqz(b, a, npt, fs); % find frequency response

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