Mumbai University > Computer Engineering > Sem 3 > Electronic Circuits and Communication Fundamentals

Marks: 5 Marks

Year: Dec 2013

The difference between PAM, PPM & PWM is as shown below:

PAM

In PAM, the modulating signal modulates the carrier pulse amplitude. The amplitude of high frequency carrier is varied in accordance with the sampled values of message signal.

The figure depicts time domain representation of the PAM technique which mentions analog message signal and PAM modulated signal as output.

PPM

The PPM signal is a pulse signal which pulse position is proportional to the amplitude of the modulating signal amplitude. The time domain representation of PPM is mentioned in the figure.

555 Timer IC is most popular to generate waveforms for PPM and PWM modes. PWM is generated using 555 timer in monostable multivibrator mode. PPM is generated using 555 timer by using PWM as a trigger signal in monostable multivibrator mode.

PWM

The PWM signal is a pulse signal which pulse width is proportional to the amplitude of the modulating analog signal.

The figure depicts time domain representation of the PWM. One of the applications of PWM is in speed control of the DC motor.

The following table summarizes difference between PAM, PWM and PPM.