Signals and Systems - Electrical Engineering

688 C H A P T E R 11: Introduction to the Design of Discrete Filters

FIGURE 11.24

High-pass FIR filter design

using Kaiser window.

0 510

−0.1

0

0.1

0.2

h[

n]

n

− 80

− 100

− 60

− 40

− 20

0

20log10|

H(

je

ω)|(dB)

0 0.5 1

ω/π

0 0.5 1

0

0.2

0.4

0.6

0.8

1

ω/π

|H

(e

jω

)|

− 2

0

2

4

6

<H

(e

jω

)

0 0.5 1

ω/π

The functionfircan be used to design low-pass, high-pass, and band-pass FIR filters using differ-

ent types of windows. When designing high-pass and band-pass FIRs,firfirst designs a prototype

low-pass filter and then uses the modulation property to shift it in frequency to a desired center

frequency.

function [b] = fir(N,wc,wo,wind)

%

% FIR filter design using window method and

% frequency modulation

%

% N : order of the FIR filter

% wc : normalized cutoff frequency (between 0 and 1)

% of low-pass prototype

% wo : normalized center frequency (between 0 and 1)

% of high-pass, bandpass filters

% wind : type of window function

% 1 : rectangular

% 2 : hanning

% 3 : hamming

% 4 : kaiser

% [b] : coefficients of designed filter

%

% USE:

% [b] = fir(N,wc,wo,wind)

%