What is Clock Data Recovery (CDR)?
Some raw data streams (such as the ones sent from the magnetic disk of a hard drive) are sent without the necessary clock signal. The process of recovering this signal is known as clock data recovery or CDR.
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Clock Data Recovery
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Clock data recovery is the process of extracting and reconstructing clock and data information from a single data stream that doesn't contain a clock signal during serial data transmission. The receiver of the data stream generates a signal, then aligns to the transitions in the data stream with a phase-locked loop.
Serial Data Transmission
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Serial data transmission is the most commonly used means of transferring digital data from one point to another. It is a form of serial interface in which one bit of data is transferred after the other.
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Clock Signal
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When data is transmitted digitally, the clock signal is the signal that coordinates the actions of circuits by oscillating between a high and low state while maintaining a consistent frequency.
Phase-Locked Loop
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A phase-locked loop is an electronic circuit consisting of a variable frequency oscillator and a phase detector that compares the phase of the signal derived from the oscillator to an input signal. It then generates an output signal whose phase is related to the phase of the input signal. Phase lock loops are commonly used in radios and computers.
Mechanics
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The receiver of the data stream uses a frequency reference present within the data stream to generate clock data. The frequency reference must transition enough times to correct any drift in the phase-locked loop's oscillator. To ensure the frequency of these transitions, some kind of coding within the data stream is necessary.
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