% first order of IIR notch filter
% Use bilinear meathod

clear;
Gb2=0.5;
w0=0.35*pi;
deltaw=0.1*pi;
b=1/(1+tan(deltaw/2)*(sqrt(1-Gb2)/sqrt(Gb2)));
B=[1 -2*cos(w0) 1].*b;
A=[1 -2*b*cos(w0) (2*b-1)];
w=0:pi/500:pi;
H=freqz(B,A,w);
plot(w/pi,abs(H));
grid;