Toa EXES-6000, Operating And Troubleshooting

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3. Principle of Time Division
3-1. PAM (Pulse Amplitude Modulation) Signal
In order to convert an analog signal such as
speech into a pulse stream, a circuit must sample
it at periodic intervals. The amplitude of the pulses
sampled is proportional to the amplitude of the
original signal at the sampling instant. This pro-
cess is called Pulse Amplitude Modulation or
simply PAM.
3-2. PAM Signal Generating Process
Fig.7 Waveforms for PAM Signal
After being modulated by the sampling pulses
having periodic intervals (Fig. 7-(b)), the analog
signal (Fig. 7-(a)) is converted into such PAM
signal as is shown in Fig. 7-(c). However, the real
pulse intervals are so short that the "spurious"
original analog signal in Fig. 7-(c) and the original
signal in Fig. 7-(a) are almost identical.
Fig. 8 shows the PAM signal generating process.
In its block diagram, the analog signal (Fig. 7-(a))
applied to the input is chopped by the ON and
OFF operation of the switch. The switching is
controlled by the sampling pulses with their high
level causing the switch on and their low level the
switch off. Through this process, the PAM signal
(Fig. 7-(c)) is delivered to the output.
Fig.8 PAM Signal Generating Process
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