| 摘要 |
A PLL circuit used in an apparat as for reading and writing data to a disk compensates for noise which causes a false clock signal or for missing clock signals which can be caused by a scratch or smudge on the surface of the disc. The PLL circuit includes a phase comparator for comparing a phase of a reference signal with a phase of a feedback signal and generates a phase difference signal. A charge pump receives the phase difference signal and generates an output signal, which is filtered by a low pass filter. The filtered signal is provided to a voltage controlled oscillator, which generates an oscillation output signal. A divider divides the oscillation output signal and generates the feedback signal. A time information generating circuit generates time information of the oscillation output signal, indicating the time period where it is presumed the reference signal is or should be received. A control circuit, using the time information, permits the output of the oscillation output signal when the reference signal is input during the presumed time period and maintains the output of the oscillation output signal when the reference signal is not received during the presumed time period.
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