Browse Definitions :
Definition

phase modulation (PM)

Also see modulation and phase-shift keying.

Phase modulation (PM) is a method of impressing data onto an alternating-current (AC) waveform by varying the instantaneous phase of the wave. Thisscheme can be used with analog or digital data.

In analog PM, the phase of the AC signalwave, also called the carrier, varies in a continuous manner. Thus, thereare infinitely many possible carrier phase states. When the instantaneous data inputwaveform has positive polarity, the carrier phase shifts in one direction; when theinstantaneous data input waveform has negative polarity, the carrier phase shifts in theopposite direction. At every instant in time, the extent of carrier-phase shift(the phase angle) is directly proportional to the extent to which the signalamplitude is positive or negative.

In digital PM, the carrier phase shifts abruptly, rather than continuouslyback and forth. The number of possible carrier phase states is usually a power of2. If there are only two possible phase states, the mode is called biphasemodulation. In more complex modes, there can be four, eight, or more differentphase states. Each phase angle (that is, each shift from one phase state to another)represents a specific digital input data state.

Phase modulation is similar in practice to frequency modulation (FM). When theinstantaneous phase of a carrier is varied, the instantaneous frequency changes as well. The converse also holds: When the instantaneous frequency is varied, theinstantaneous phase changes. But PM and FM are not exactly equivalent, especially inanalog applications. When an FM receiver is used to demodulate a PM signal, or whenan FM signal is intercepted by a receiver designed for PM, the audio is distorted. This is because the relationship between phase and frequency variations is not linear;that is, phase and frequency do not vary in direct proportion.

This was last updated in September 2005

Start the conversation

Send me notifications when other members comment.

Please create a username to comment.

-ADS BY GOOGLE

File Extensions and File Formats

SearchCompliance

SearchSecurity

  • cybersecurity

    Cybersecurity is the protection of internet-connected systems, including hardware, software and data, from cyberattacks.

  • asymmetric cryptography (public key cryptography)

    Asymmetric cryptography, also called public key cryptography, uses a pair of numerical keys that are mathematically related to ...

  • digital signature

    A digital signature is a mathematical technique used to validate the authenticity and integrity of a message, software or digital...

SearchHealthIT

SearchDisasterRecovery

  • business continuity plan (BCP)

    A business continuity plan (BCP) is a document that consists of the critical information an organization needs to continue ...

  • disaster recovery team

    A disaster recovery team is a group of individuals focused on planning, implementing, maintaining, auditing and testing an ...

  • cloud insurance

    Cloud insurance is any type of financial or data protection obtained by a cloud service provider. 

SearchStorage

  • hard disk drive (HDD)

    A computer hard disk drive (HDD) is a non-volatile memory hardware device that controls the positioning, reading and writing of ...

  • byte

    In most computer systems, a byte is a unit of data that is eight binary digits long. Bytes are often used to represent a ...

  • network-attached storage (NAS)

    Network-attached storage (NAS) is dedicated file storage that enables multiple users and heterogeneous client devices to retrieve...

Close