| 摘要 |
A PLL circuit comprises a circuit which issues an alarm when fluctuation of the potential of a DC power source connected to the PLL circuit exceeds a predefined range. A first potential generation circuit generates a first potential higher than a steady-state potential of the DC power source. A second potential generation circuit generates a second potential lower than the steady-state potential of the DC power source. A first comparator circuit compares a local maximum potential of the DC power source with the first potential. A second comparator circuit compares a local minimum potential of the DC power source with the second potential. A supply circuit supplies a drive voltage to an alarm issuer, in a case where the local maximum potential is higher than the first potential, and/or the local minimum potential is lower than the second potential, based on the comparison results.
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