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134
Baseband Pulse and Digital Signaling Chap. 3
w(t)
0
t
(a) Baseband Analog Waveform
s(t)
t
0
T s
(b) Switching Waveform with Duty Cycle d = t/T s = 1/3
t
w s (t)
t
t
0
T s
(c) Resulting PAM Signal (natural sampling, d = t/T s = 1/3)
Figure 3–1
PAM signal with natural sampling.
where
is a rectangular wave switching waveform and f s = 1T s Ú 2B.
THEOREM.
s(t) =
a
q
k=-q
The spectrum for a naturally sampled PAM signal is
W s (f) = [w s (t)] = d a
q
ßa t - kT s
b
t
n=-q
sin pnd
pnd W(f - nf s)
(3–2)
(3–3)