Design of a digital low pass Butterworth filter (IIR)

MATLAB CODE:

PBE=400; %Pass band edge frequency= 400 Hz
SBE=800; %Stop band edge frequency= 800 Hz
Fs=2000; %Sampling frequency= 2000 Hz
Wp=2*PBE/Fs;
Ws=2*SBE/Fs;
W=0:1/Fs:pi;
Rs=30;    %Stop band attenuation= 30 dB
Rp=0.4;  %Pass band attenuation= 0.40 dB
[N,Wn]=buttord(Wp,Ws,Rp,Rs);
[b,a]=butter(N,Wn);
zplane(b,a);
figure;
[H,W]=freqz(b,a);
freqz(b,a);
figure;
plot(W,20*log10(abs(H)));

RESULTs:

POLES and Zeroes in Z-plane

fig8_cs

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