| 摘要 |
<p>PURPOSE:To satisfy standards relating to variation in a clock phase by sharply reducing the phase variation of an output clock from a clock unit. CONSTITUTION:When previously set fixed time has elapsed from the input of a fault generation signal from a fault generation part 11, a normal switching protection time counter 15 informs a switching protection time setting part 17 of the lapse of the time. When minimum time required for the switching of a reference clock has elapsed from the input of the fault generation signal from the detection part 11, a minimum switching protection time counter 16 informs the setting part 17 of the lapse of the time. When a reference clock to be used next had been set up before the generation of the fault, the setting part 17 resets a setting/resetting circuit 18 based upon information from the counter 16. When the circuit 18 is reset, the switching of a selector 19 is controlled to select an output from an N-frequency division counter 13.</p> |
