Pulse-amplitude modulation, acronym 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 amplitude of train of carrier pulse are varied according to the sample value of the message signal.
Example: A two-bit modulator will take two bits at a time and will map the signal amplitude to one of four possible levels, for example −3 volts, −1 volt, 1 volt, and 3 volts.
Demodulation is performed by detecting the amplitude level of the carrier at every symbol period.
Generation of PAM
The signal is sampled at regular intervals and each sample is made proportional to the magnitude of the signal at the instant of sampling. These sampled pulses may then be sent either directly by a channel to the receiving end or may be made to modulated using a carrier wave before transmission.
For the generation of a PAM signal we use a flat top type PAM scheme because during the transmission,the noise is interfered at top of the transmission pulse which can be easily removed if the PAM pulse in flat top.