PAM is the simplest form of data modulation .The amplitude of uniformly spaced pulses is varied in proportion to the corresponding sample values of a continuous message m (t).

A PAM waveform consists of a sequence of flat-topped pulses. The amplitude of each pulse corresponds to the value of the message signal x (t) at the leading edge of the pulse.

The pulse amplitude modulation is the process in which the amplitudes of regularity spaced rectangular pulses varies with the instantaneous sample values of a continuous message signal in a one-one fashion. A PAM wave is represented mathematically as,

Where,   
x (nT_s) = represents the nth sample of the message signal x(t),      
K = is the sampling period,
K_a = constant called amplitude sensitivity,      
P(t) = denotes a pulse.

PAM is of two types,

1. Double polarity PAM = This is the PAM wave which consists of both positive and negative pulses as shown in figure.
2. Single polarity PAM = This consists of PAM wave of only either negative (or) Positive pulses. In this the fixed dc level is added to the signal to ensure single polarity signal. It is represented as

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