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 de-normalization 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 cut-off for bandpass and the lower cut-off 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((wc2-wc1)/2)); beta = (cot((wc2-wc1)/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