Compare PAM, PWM and PPM
PAM, PWM and PPM stands for Pulse Amplitude Modulation, Pulse Width Modulation and Pulse Position Modulation. In the PAM system carrier signal is rectangular pulse and that is why this system is called PAM. In the pulse amplitude modulation technique the amplitude of the carrier signal is varied according to the modulating signal.
In the PWM system, the width of the carrier pulse is modulated according to the message signal. The width of the pulse is maximum at the positive peak of the message signal and minimum at the negative peak of the message signal.
In the PPM system, the position of the carrier pulse is modulated according to the message signal. The position of the pulse is shifted maximum at the positive peak of the message signal and minimum shifted at the negative peak of the message signal. All the three modulation techniques are analog modulation techniques.
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Fig.23