Clock recovery: Difference between revisions
linked some telecom line coding schemes |
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* [[Manchester code]] |
* [[Manchester code]] |
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* [[64B/66B encoding]] |
* [[64B/66B encoding]] |
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* [[B8ZS]] encoding |
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* [[HDB3]] encoding |
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[[Category:Electrical circuits]] |
[[Category:Electrical circuits]] |
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[[Category:Clock signal]] |
[[Category:Clock signal]] |
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[[Category:Line codes]] |
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Revision as of 08:23, 8 February 2007
Some digital data streams, especially high-speed serial data streams (such as the raw stream of data from the magnetic head of a disk drive) are sent without an accompanying clock. The receiver generates a clock from an approximate frequency reference, and then phase-aligns to the transitions in the data stream with a phase-locked loop (PLL). This process is commonly known as clock and data recovery (CDR).
In order for this scheme to work, a data stream must transition frequently enough to correct for any drift in the PLL's oscillator. The limit for how long a clock recovery unit can operate without a transition is known as its maximum consecutive identical digits (CID) specification. To ensure frequent transitions, some sort of encoding is used; 8B/10B encoding is very common, while Manchester encoding serves the same purpose in old revisions of 802.3 local area networks.