| 摘要 |
PURPOSE:To output always stable disk data by supplying the output of a reference voltage source to a voltage control oscillator with a changing-over circuit and evading the deviation to an uncontrollable frequency due to a disturbance, etc. CONSTITUTION:When the frequency of a decoding clock DCLK outputted from a voltage control oscillator VCO3 by the disturbance, etc., exceeds a control range. A changing-over signal SEL is outputted from a frequency comparator 5 to a changing-over circuit 7. When the circuit 7 receives the signal SEL, a reference control voltage BV from a reference voltage source 6 is supplied to the VCO3 instead of a control voltage CV from the circuit 2, the VCO3 is oscillated based on a voltage BV and the clock DCLK is outputted. When the frequency of the DCLK is returned to a normal voltage, the output of the signal SEL is turned off, the circuit 7 is returned to the usual changing-over condition, the voltage CV generated by the circuit 2 is supplied to the VCO3 and a clock control circuit is returned to a usual action. |
