Chapter 9

% Program 9_1

% Elliptic IIR Lowpass Filter Design

%

Wp = input('Normalized passband edge = ');

Ws = input('Normalized stopband edge = ');

Rp = input('Passband ripple in dB = ');

Rs = input('Minimum stopband attenuation in dB = ');

[N,Wn] = ellipord(Wp,Ws,Rp,Rs)

[b,a] = ellip(N,Rp,Rs,Wn);

[h,omega] = freqz(b,a,256);

plot (omega/pi,20*log10(abs(h)));grid;

xlabel('\omega/\pi'); ylabel('Gain, dB');

title('IIR Elliptic Lowpass Filter');

% Program 9_2

% Type 1 Chebyshev IIR Highpass Filter Design

%

Wp = input('Normalized passband edge = ');

Ws = input('Normalized stopband edge = ');

Rp = input('Passband ripple in dB = ');

Rs = input('Minimum stopband attenuation in dB = ');

[N,Wn] = cheb1ord(Wp,Ws,Rp,Rs);

[b,a] = cheby1(N,Rp,Wn,'high');

[h,omega] = freqz(b,a,256);

plot (omega/pi,20*log10(abs(h)));grid;

xlabel('\omega/\pi'); ylabel('Gain, dB');

title('Type I Chebyshev Highpass Filter');

% Program 9_3

% Design of IIR Butterworth Bandpass Filter

%

Wp = input('Passband edge frequencies = ');

Ws = input('Stopband edge frequencies = ');

Rp = input('Passband ripple in dB = ');

Rs = input('Minimum stopband attenuation = ');

[N,Wn] = buttord(Wp, Ws, Rp, Rs);

[b,a] = butter(N,Wn);

[h,omega] = freqz(b,a,256);

gain = 20*log10(abs(h));

plot (omega/pi,gain);grid;

xlabel('\omega/\pi'); ylabel('Gain, dB');

title('IIR Butterworth Bandpass Filter');

% Program 9_4

% Group-delay equalization of an IIR filter.

%

[n,d] = ellip(4,1,35,0.3);

[GdH,w] = grpdelay(n,d,512);

plot(w/pi,GdH); grid

xlabel('\omega/\pi'); ylabel('Group delay, samples');

title('Original Filter');

pause

F = 0:0.001:0.3;

g = grpdelay(n,d,F,2); % Equalize the passband

Gd = max(g)-g;

% Design the allpass delay equalizer

[num,den,tau] = iirgrpdelay(8, F, [0 0.3], Gd);

[GdA,w] = grpdelay(num,den,512);

plot(w/pi,GdH+GdA); grid

xlabel('\omega/\pi');ylabel('Group delay, samples');

title('Group Delay Equalized Filter');