| 摘要 |
A phase locked loop circuit includes a phase comparator, a loop filter, a controlled oscillator, a limiter, a frequency divider, an unlock detecting circuit and a switch. The phase comparator compares an index signal and a reference signal. The loop filter smoothes an output signal of the phase comparator. The controlled oscillator oscillates at a frequency in accordance with an output signal of the loop filter. The limiter connected between an output of the phase comparator and an input of the controlled oscillator. The limiter limits level of a signal passing therethrough at a predetermined range. The frequency divider divides an output signal of the controlled oscillator and generates the reference signal. The unlock detecting circuit outputs the unlocking of a phase lock based on the index signal and the reference signal. The switch shuts up an output signal of the loop filter based on an unlock detecting signal.
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