Analog-digital converting apparatus and clock signal output apparatus

1. An analog-digital converting apparatus for converting an analog video signal inputted from an exterior containing a composite synchronizing signal into a digital video signal, comprising:

a voltage controlled oscillator for outputting a clock signal having an oscillation frequency in accordance with an input voltage;

a convertor for converting the analog video signal inputted from the exterior into the digital video signal synchronized with the clock signal outputted from the voltage controlled oscillator;

a phase difference detector for detecting a phase difference between the composite synchronizing signal in the analog video signal and a feedback signal which corresponds to the clock signal from the voltage-controlled oscillator; and

a voltage control unit for controlling the input voltage of the voltage controlled oscillator to change in response to the phase difference detected by the phase difference detector when the phase difference is within a certain range, and to maintain the input voltage intact when the phase difference is in exceed of the certain range.

2. The analog-digital converting apparatus according to claim 1 , wherein the phase difference detector outputs a first value corresponding to the detected phase difference, and

the voltage control unit includes:

a selector for selecting either the first value or a second value which is predetermined value, the selector selecting the first value when the phase difference is within the certain range, the selector selecting the second value when the phase difference is in exceed of the certain range; and

a voltage output unit for outputting the input voltage corresponding to the value selected by the selector to the voltage controlled oscillator.

3. The analog-digital converting apparatus according to claim 2 , wherein the voltage control unit further includes a memory storing the second value, and

the selector selects the second value in the memory when the phase difference is in exceeding of the certain range.

4. The analog-digital converting apparatus according to claim 1 , wherein the phase difference detector outputs a first value corresponding to the detected phase difference, and

the voltage control unit includes:

a processor for processing, selecting the first value when the phase difference is within the certain range, and selecting the second value when the phase difference is in exceeding of the certain range; and

a voltage output unit for outputting the input voltage corresponding to the value selected by the processor to the voltage controlled oscillator.

5. A clock signal output apparatus for outputting a clock signal to an analog-digital convertor, the analog-digital convertor converting an analog video signal inputted from an exterior into a digital video signal synchronized with the clock signal, the clock signal output apparatus comprising:

a voltage controlled oscillator for outputting the clock signal having an oscillation frequency in accordance with an input voltage;

a phase difference detector for detecting a phase difference between the composite synchronizing signal in the analog video signal and a feedback signal which corresponds to the clock signal from the voltage-controlled oscillator; and

a voltage control unit for controlling the input voltage of the voltage controlled oscillator to change in response to the phase difference detected by the phase difference detector when the phase difference is within a certain range, and to maintain the input voltage intact when the phase difference is in exceed of the certain range.

6. The clock signal output apparatus according to claim 5 , wherein the phase difference detector outputs a first value corresponding to the detected phase difference, and

the voltage control unit includes:

a selector for selecting either the first value or a second value which is predetermined value, the selector selecting the first value when the phase difference is within the certain range, the selector selecting the second value when the phase difference is in exceed of the certain range; and

a voltage output unit for outputting the input voltage corresponding to the value selected by the selector to the voltage controlled oscillator.

7. The clock signal output apparatus according to claim 6 , wherein the voltage control unit further includes a memory storing the second value, and

the selector selects the second value in the memory when the phase difference is in exceeding of the certain range.

8. The clock signal output apparatus according to claim 5 , wherein the phase difference detector outputs a first value corresponding to the detected phase difference, and

the voltage control unit includes:

a processor for processing, selecting the first value when the phase difference is within the certain range, and selecting the second value when the phase difference is in exceeding of the certain range; and

a voltage output unit for outputting the input voltage corresponding to the value selected by the processor to the voltage controlled oscillator.