06 December 2007

IIR Filter

Frequency Response of a IIR Filter

Logic:

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"

Algorithm:

  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

%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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