% Routine 10.1 Bode Plots
%
% JV (10/22/2002): modified with subplots to illustrate
%    the effects of the Q in filter (10.20)
%
fmin = 0;              % min freq (in Hz) to view
fmax = .5;             % max freq (in Hz) to view
df = 0.01;             % step size
f = fmin:df:fmax;      % frequency vector
w = 2*pi*f;            % radian freq vector
s = w*i; 
Q = 2;
N = s./Q;              % numerator of transfer fn
D = s.*s  + s./Q + 1;  % denominator
H = N./D;              % transfer fn
r = abs(H);            % gain at freq w
phi = angle(H);        % phase lead
subplot(2,2,1)
plot(f,r)              % gain vs freq in Hz for Q = 2
Q = 4;
N = s./Q;              % numerator of transfer fn
D = s.*s  + s./Q + 1;  % denominator
H = N./D;              % transfer fn
r = abs(H);            % gain at freq w
phi = angle(H);        % phase lead
subplot(2,2,2)
plot(f,r)              % gain vs freq in Hz for Q = 4
Q = 8;
N = s./Q;              % numerator of transfer fn
D = s.*s  + s./Q + 1;  % denominator
H = N./D;              % transfer fn
r = abs(H);            % gain at freq w
phi = angle(H);        % phase lead
subplot(2,2,3)
plot(f,r)              % gain vs freq in Hz for Q = 8
Q = 16;
N = s./Q;              % numerator of transfer fn
D = s.*s  + s./Q + 1;  % denominator
H = N./D;              % transfer fn
r = abs(H);            % gain at freq w
phi = angle(H);        % phase lead
subplot(2,2,4)
plot(f,r)              % gain vs freq in Hz for Q = 16