Digital Signal Processing Reference
In-Depth Information
Signal
Sampled signal
0
T
2
T
3
T
4
T
t
Figure 1.22
Pulse-amplitude modulation.
3
1
3
1
1
1
3
n
n
2
n
0
T
2
T
3
T
t
2
2
Figure 1.23
Time-division multiplexing.
Multiplexer
Demultiplexer
D/A
1
1
Transmission
channel
2
A/D
D/A
2
D/A
n
n
Synchronizing
signal
Control
signals
Figure 1.24
Multiplexed pulse-code-modulated telephone transmission.
the signals are separated in time. This figure is simplified somewhat; information
must be included with the signal that enables the receiving circuits to assign the
pulses to the correct signals. This process is called
synchronization
.
If the sampling is performed by an analog-to-digital converter, the sample
values are in binary and the process is called
pulse-code modulation
. Figure 1.24
illustrates the hardware of a time-division-multiplexed telephone system. The
control signals switch each telephone signal to the analog-to-digital converter in
