| 摘要 |
PURPOSE:To detect step-out, and to generate an alarm information immediately and exactly, by detecting the case when a reference pulse and a feedback pulse do not appear alternately and regularly in an input of a phase comparing circuit. CONSTITUTION:To an AND circuit 10, a reference pulse of a phase comparator 1 and an output of Q are inputted through a delaying circuit 12. To a circuit 11, a feedback pulse and an output of -Q are inputted through a delaying circuit 13. To an OR circuit 9, outputs of the circuits 10, 11 are inputted. In case when a feedback type phase controlling circuit (hereinafter called a PLL circuit) is normal, a time difference between the reference pulse and the feedback pulse is controlled so as to become almost constant, and the circuits 10, 11 generate no output. If an abnormal state occurs, an output is generated in the circuit 10 or 11, and it is sent out as an alarm signal through the circuit 9. Accordingly, it is possible to detect such an abnormal state as step-out and to generate an alarm exactly and immediately without being influenced by a variation of an electric power supply. |
