| 摘要 |
PURPOSE:To obtain a circuit small in jittering, can be converted easily to IC and can executed a high stable operation, by filtering the phase comparing information from a phase comparator, by a loop filter using an up-down counter, and bringing an oscillation use capacity to a variable control stepwise by a phase signal which is filtered. CONSTITUTION:Based on phase comparing information, a control signal for adding and eliminating the capacity is generated by an up-down counter 2, and a capacity controlling circuit 3 brings a switch group in a variable capacity circuit 4, to an on-off control, based on a control signal. In this case, the variable capacity circuit 4 is constituted of a capacitor block 4A and a capacitor block 4B, and in case the capacity is increased by a signal from the capacity controlling circuit 3, the switch in the block A is turned on by the capacity increase portion, and on the other hand, in case the capacity is decreased, the switch in the block 4B is turned off by the capacity decrease portion. As this capacity is varied, an oscillation frequency is varied in an oscillator 5 using a quartz oscillator, and an output of the oscillator 5 is provided as a reference clock (b) to a phase comparator 1 through a frequency divider 6.
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