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Vivek
Posts:
3
Registered:
11/10/12


IIR Bandpass Filter Design
Posted:
Nov 17, 2012 10:26 PM


Hi I posted a question earlier, but it got few responses. I need help in this because I am using MATLAB for the first time.
Can someone tell me how I can get the zeros and poles of a digital bandpass filter I created from an analog lowpass prototype? I did denormalization of the poles and zeros and created a function for bilinear transform. Then I implemented spectral transform from the digital poles, zeros and gain. I have two problems:
1. When I plot this against omega, I get it like a bandstop filter (if the range of omega is 0 to pi). Should I take negative values? 2. My function takes the input arguments as digital zeros, digital poles, digital gain, desired upper and lower cutoff for bandpass and the lower cutoff of the lowpass and finally the frequency variable (7 inputs). And the output argument is the magnitude of the bandpass. I have defined it as follows:
function [ H_band ] = trand_bandpass(Zd,Pd,Kd,wc1,wc2,wc,omega) Product_Z = 1; Product_P = 1; Zeros = numel(Zd); Poles = numel(Pd);
z_tilda = exp(1)^(1i*omega);
alpha = (cos((wc1+wc2)/2))/(cos((wc2wc1)/2)); beta = (cot((wc2wc1)/2))*(tan(wc/2)); A = (2*alpha*beta)/(beta + 1); B = (beta  1)/(beta + 1); up = ((z_tilda)^(2))(A*((z_tilda)^(1)))+B; down = (B*((z_tilda)^(2)))(A*((z_tilda)^(1)))+1; ze = up/down;
for r = 1:Zeros Product_Z = Product_Z*(ze Zd(r)); end for r = 1:Poles Product_P = Product_P*(ze  Pd(r)); end
H_b = Kd*(Product_Z)*((1+ze)^(PolesZeros))/(Product_P); H_band = abs(H_b);
end
Can someone help me return the zeros, poles and gain of this filter?



