casual IIR filter

4. Program illustrates the design of a causal IIR filter, its simulation in transposed Direct Form II, and its application in filtering a signal.

% Program P8_3

% Illustration of Filtering by an IIR Filter

%

clf;

% Generate the input sequence

k = 0:50;

w2 = 0.7*pi;w1 = 0.2*pi;

x1 = 1.5*cos(w1*k); x2 = 2*cos(w2*k);

x = x1+x2;

% Determine the filter transfer function

[N, Wn] = ellipord(0.25, 0.55, 0.5, 50);

[num, den] = ellip(N,0.5, 50,Wn);

% Generate the output sequence

y = filter(num,den,x);

% Plot the input and the output sequences

subplot(2,1,1);

stem(k,x); axis([0 50 -4 4]);

xlabel(’Time index n’); ylabel(’Amplitude’);

title(’Input Sequence’);

subplot(2,1,2);

stem(k,y); axis([0 50 -4 4]);

xlabel(’Time index n’); ylabel(’Amplitude’);

title(’Output Sequence’);