Digital Signal Processing Reference
In-Depth Information
transmitted in the same channel, with the signals separated in time, but not in fre-
quency. Each signal is pulse-amplitude modulated as described earlier, with no
overlap in time of the signals.
Figure 6.44(a) illustrates a simple system for the pulse-amplitude modulation
and time-division multiplexing of three signals. The electronic switches are controlled
by the signals and which are depicted in Figure 6.44(b), so that the
circuit is completed to the three modulation signals, in order. At the receiving end of
the transmission, another electronic switch, which is synchronized with the multiplexer
switch, is used to demultiplex (separate) the time-division-multiplexed signal into
three separate signals. The signal
s
1
(t), s
2
(t),
s
3
(t),
y
i
(t)
is the pulse-amplitude-modulated signal of
x
i
(t), i = 1, 2, 3.
The demodulation of
y
i
(t)
is accomplished with a low-pass filter, as
Electronic
switches
Electronic
switches
x
1
(
t
)
y
1
(
t
)
y
1
d
(
t
)
s
1
(
t
)
s
1
(
t
)
x
2
(
t
)
y
2
(
t
)
y
tm
(
t
)
y
2
d
(
t
)
s
2
(
t
)
s
2
(
t
)
x
3
(
t
)
y
3
(
t
)
y
3
d
(
t
)
s
3
(
t
)
s
3
(
t
)
Multiplexer
Demultiplexer
(a)
s
1
(
t
)
t
a
t
a
t
T
c
s
2
(
t
)
t
a
T
c
/3
t
s
3
(
t
)
t
a
2
T
c
/3
t
(b)
H
( )
y
i
d
(
t
)
x
i
d
(
t
)
H
( )
co
co
0
Demodulator
Figure 6.44
A system for time-division
(c)
multiplexing.
