Pulse Modulation & its types

Pulse Modulation

-      consists essentially of sampling analog information signals and then converting those samples into discrete pulses and transporting the pulses from a source to a destination over a physical transmission medium

The four predominant methods of pulse modulation:

-      pulse width modulation

-      pulse position modulation

-      pulse amplitude modulation

-      pulse code modulation

Forms of Pulse modulation

Pulse Width Modulation (PWM)

-      is sometimes called pulse duration modulation (PDM) or pulse length modulation (PLM)

-      the width of a constant amplitude pulse is varied proportional to the amplitude of the analog signal at the time the signal is sampled

-      used in special-purpose communications system mainly for the military but are seldom used for commercial digital transmission

                             

Pulse Position Modulation (PPM)

-      the position of a constant-width pulse within a prescribed time slot is varied according to the amplitude of the sample of the analog signal

-      the higher the amplitude of the sample, the farther to the right the pulse is positioned within the prescribed time slot

-      the highest amplitude sample produces a pulse to the far right, and the lowest amplitude sample produces a pulse to the far left

-      also used in special-purpose communications system mainly for the military but are seldom used for commercial digital transmission

Pulse Amplitude Modulation (PAM)

-      the amplitude of a constant width, constant-position pulse is varied according to the amplitude of the sample of the analog signal

-      PAM waveforms resemble the original analog signal more than the waveforms for PWM or PPM

-      this is used as an intermediate form of modulation with PSK, QAM, and PCM, although it is seldom used by itself

Pulse Code Modulation (PCM)

-      the analog signal is sampled and then converted to a serial n-bit binary code for transmission

-      each code has the same number of bits and requires the same length of time for transmission