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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.
Example: A two bit modulator (4-PAM) 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.
Pulse-amplitude modulation is now rarely used, having been largely superseded by pulse-code modulation, and, more recently, by pulse-position modulation.
In particular, all telephone modems faster than 300 bits/s use quadrature amplitude modulation (QAM). (QAM uses a two-dimensional constellation).
See also
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