Question

Part I    Design of a DC Blocker FilterPart I    Design of a DC Blocker Filter

Design a digital filter to block DC signal using

- Plot the frequency response of your filter

1. FIR filter
2. IIR filter

Answer 1

*Since only constraint is to block DC, So only requirement is that it should have a zero at z = 1.

(a) Simplest FIR filter to achieve it is

                                                                

(b) Simplest IIR filter is

                                                            

Since IIR filter has to be stable, so its pole should lie within unit circle. So

                                                                           

Lets choose a = 0.5. So

                                                                        

MATLAB code to generate frequency response is shown below:

w = (-pi:2*pi/1000:pi);
z = exp(j*w);
HFIR = (1-z.^(-1));
HIIR = (1-z.^(-1))./(1-0.5*z.^(-1));
plot(w/pi,abs(HFIR))

hold all

grid on

plot(w/pi,abs(HIIR))

xlabel('\omega/\pi')

ylabel('magnitude')
legend('FIR filter','IIR Filter')
figure;
plot(w/pi,angle(HFIR)/pi*180)
hold all
grid on

plot(w/pi,angle(HIIR)/pi*180)

xlabel('\omega/\pi')

ylabel('phase(degree)')

legend('FIR filter','IIR Filter')

Magnitude response for both FIR and IIR filter is shown below:

Phase response for both FIR and IIR filter is shown below: