Digital Signal Processing Reference
In-Depth Information
1
0.5
0
-0.5
-20
-15
-10
-5
0
5
10
15
20
x
1
0.8
0.6
0.4
0.2
0
0
0.5
1
1.5
2
2.5
3
Radians
FIGURE 2.20
Sample-and-hold lowpass filtering effect.
:
H
h
ðfÞ¼pfT
(2.17)
The plot of the magnitude effect is shown in
Figure 2.20
.
The magnitude frequency response acts like lowpass filtering and shapes the sampled signal
spectrum of
Y
s
ðf Þ
. This shaping effect distorts the sampled signal spectrum
Y
s
ðf Þ
in the desired
frequency band, as illustrated in
Figure 2.21
. On the other hand, the spectral images are attenuated
Yf
s
()
Y
()
Y
f
(
−
f
s
)
Yf
(
−
2
f
s
)
Spectral images
Sample-and-hold effect
sin( )
x
x
f
0
2
f
s
f
s
FIGURE 2.21
Sample-and-hold effect and distortion.
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