| 摘要 |
PURPOSE:To prevent a frequency of an input clock from being changed largely by fixing an input voltage of a voltage controlled oscillator to a prescribed value when the interruption of the input clock is detected. CONSTITUTION:The circuit consists of a phase comparator 1 outputting a pulse whose width is proportional to a difference of a phase of an input clock 10 and that of a feedback clock 20, a low pass filter 2 outputting a voltage resulting from smoothing an input pulse from the phase comparator 1, an amplifier 3 having a negative feedback resistor 5 and amplifying a voltage inputted from the low pass filter 2, a voltage controlled oscillator 4 outputting the feedback clock 20 in response to an output voltage from the amplifier 3 and a detector 6 using a switch 7 to short-circuit the negative feedback resistor 5 when the input clock 10 is interrupted. When the input clock 10 is interrupted, the detector 6 closes the switch 7 thereby bringing the frequency of the output clock 10 to be almost equal to the frequency of the input clock 10 applied usually. |
