B. P. Lathi, Zhi Ding - Modern Digital and Analog Communication Systems-Oxford University Press (2009)

260 SAMPLING AND ANALOG-TO-DIGITAL CONVERSION
Figure 6.8
Aliasing effect.
(a) Spectrum of a
practical signal
g(t).
(b) Spectrum of
sampled g(t).
(c) Reconstructed
signal spectrum.
(d) Sampling
scheme using
antialiasing filter.
(e) Sampled
signal spectrum
(dotted) and the
reconstructed
signal spectrum
(solid) when
antialiasing filter
is used.
-j/2
0
(a)
G(fl
Lost tail is
folded back
(b)
Reconstruction filter
H( f) ,.
................ ................,
Folded tail distorts
Reconstructed spectrum ! ! lower frequencies
Ga< f)
Lost tail results in loss
of higher frequencies
f/2
Lost tail
I
fs
Sample signal
f-
w -
f-
g(t)
-w/2 0 w/2 wz
-j/2 fs/2 fs
(c)
Antialiasing filter
"iaaCt)
w -
J -
(d)
-ws
0 Ws
Lost tail results in loss
of higher frequencies
-j/2 f/2 fs
(e)
w -
J-