Types
There are two types of pulse amplitude modulation:
- Single polarity PAM: In this a suitable fixed DC bias is added to the signal to ensure that all the pulses are positive.
- Double polarity PAM: In this the pulses are both positive and negative.
Pulse-amplitude modulation is widely used in baseband transmission of digital data, with non-baseband applications having been largely replaced by pulse-code modulation, and, more recently, by pulse-position modulation.
In particular, all telephone modems faster than 300 bit/s use quadrature amplitude modulation (QAM). (QAM uses a two-dimensional constellation).
Read more about this topic: Pulse-amplitude Modulation
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