Digital Modulation

Pulse-amplitude modulation (PAM) is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses. It is an analog pulse modulation scheme in which the amplitudes of a train of carrier pulses are varied according to the sample value of the message signal. 

Pulse-position modulation (PPM) is a form of signal modulation in which M message bits are encoded by transmitting a single pulse in one of possible required time shifts. This is repeated every T seconds, such that the transmitted bit rate is. bits per second.

A  PWM (pulse-width-Modulation) signal consists of two main components that define its behavior: a duty cycle and a frequency. It is used in transmission of information by encoding a message into a pulsing signal, also for power control of electronic devices such as motors and as principal algorithm for photo-voltaic solar battery chargers