| • Science | • People | • Locations | • Timeline |
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 as follows.
The constellation is one dimensional in the case of PAM. 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Pulse-amplitude modulation is now rarely used, having been largely superseded by pulse-code modulation, and, more recently, by pulse-position modulation.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).