EXPERIMENT - 5

AIM

To design a Elliptic Low pass Filter and plot it's phase and magnitude response.

THEORY

The elliptic filter is a form of RF filter that provides a very fast transition from pass-band to the ultimate roll off rate.

The elliptic filter is characterised by the fact that it has both pass-band and stop-band ripple.

Despite the ripple, the elliptic filter offers very high levels of rejection and as a result it is used in many RF filter applications where rejection levels are key.

MATLAB COMMANDS USED

* [N,Wn]=ellipord(Wp,Ws,Rp,Rs);
* [b a]=ellip(N,passband_ripple,stopband_ripple,Wn);
* [H,w]=freqz(b,a);

MATLAB CODE

%Low pass using elliptic filter.
[N,Wn]=ellipord(0.4,0.5,0.5,60);
[b,a] = ellip(N ,0.5,60,Wn);
[h w]=freqz(b,a,256);
H=abs(h);
HdB=20*log10(H);
figure (1);
plot(w/pi,H,'black','linesmoothing','on');
grid on;
title('Magnitude Repsonse of a Low pass 
Elliptic filter with Wp=0.4 and Ws=0.5 and 
attenuation at 60dB in stopband');
xlabel('Normailized Frequency ( rad/sec )');
ylabel('Gain');
axis([0 1 0 1.1]);
print('ellip_low','-dpng');


figure (2);
plot(w/pi,HdB,'black','linesmoothing','on');
grid on;
title('Magnitude Repsonse of a Low pass 
Elliptic filter with Wp=0.4 and Ws=0.5 
and ripple at 60dB in stopband');
xlabel('Normailized Frequency ( rad/sec )');
ylabel('Gain in dBs');
axis([0 1 -120 2]);

print('ellip_low_dB','-dpng');

RESULT

The Elliptic filter have been designed and response plotted. It has ripples in both stopband and passband but offers high rejection.