PAM (Pulse Amplitude Modulation)

A form of signal modulation in which the amplitude of the dig-

ital pulse carrier is modulated according to the amplitude level of the original signal. PAM samples an incoming analog signal, for example, measures its amplitude, and outputs a digital pulse of a representative amplitude.

The outgoing pulse closely matches the amplitude of the incoming signal, but when digitized in an A-to-D

converter, the digital output is the nearest of a number of standard amplitude values. PAM was used in this manner in early channel banks to interface analog PBXs and central offices (COs) to DS-1 digital circuits.

The PAM-encoded signal subsequently was further encoded using pulse code modulation (PCM) before the signal was placed on the circuit. PAM is considered obsolete in this application, having been replaced by direct

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• X.200
• X.21bis
• X.25
• X.25
• X.28
• X.29
• X.3
• X.31
• X.32
• X3T9-3
• X3T9-5
• X.400
• X.500
• X.509
• X.75
• XAUI (10 Gigabit Attachment Unit Interface)
• x-axis
• X band
• Xbar (CROSSbar)
• xDSL (generic Digital Subscriber Line)
• xDSL (generic Digital Subscriber Line)
• xDSL (generic Digital Subscriber Line)
• xerography
• Xerox PARC (Xerox Palo Alto Research Center)
• XML (eXtensible Markup Language)