Biomedical Engineering Reference
In-Depth Information
Figure 9.36 shows the frequency characteristics of four filters: low-pass, high-pass, band-
pass, and notch filters. The signal that is passed through the filter is indicated by the fre-
quency interval called the passband. The signal that is removed by the filter is indicated
by the frequency interval called the stopband. The magnitude of the filter,
, is one
in the passband and zero in the stopband. The low-pass filter allows slowly changing sig-
nals with frequency less than o
1
to pass through the filter and eliminates any signal or noise
above o
1
. The high-pass filter allows quickly changing signals with frequency greater than
o
2
to pass through the filter and eliminates any signal or noise with frequency less than o
2
.
The band-pass filter allows signals in the frequency band greater than o
1
and less than o
2
to
pass through the filter and eliminates any signal or noise outside this interval. The notch
filter allows signals in the frequency band less than o
1
and greater than o
2
to pass through
j
Hj
ðÞ
o
j
H
(
j
ω
)
Passband
Stopband
ω
ω
1
H
(
j
ω
)
Passband
Stopband
ω
ω
2
H
(
j
ω
)
Passband
Stopband
Stopband
ω
ω
1
ω
2
H
(
j
ω
)
Passband
Passband
ω
ω
1
ω
2
FIGURE 9.36
Ideal magnitude-frequency response for four filters, from top to bottom: low-pass, high-pass,
band-pass, and notch.
