Oscillation device and controlling method therefor

1. An oscillation device comprising:

a reference oscillation unit for generating an oscillating signal of a specific frequency;

a voltage-controlled oscillation unit for generating an output oscillation signal whose frequency is dependent on a control voltage;

a phase comparing unit for detecting a phase difference based on the oscillating signal and the output oscillation signal;

a digital value storage unit for storing therein a phase difference signal corresponding to the phase difference as a digital value;

a sample holding unit for intermittently renewing and maintaining a hold signal in accordance with the digital value; and

a control unit for controlling the reference oscillation unit, the phase comparing unit and the digital value storage unit to be started or stopped, and also controlling to employ as the control voltage the phase difference signal or the hold signal,

wherein the control unit performs the step of employing as the control voltage the phase difference signal, the step of operating the digital value storage unit after a specific period of time elapses or after the phase difference becomes within a specific range, and the step of employing as the control voltage the hold signal and stopping the reference oscillation unit, the phase comparing unit and the digital value storage unit,

wherein the voltage-controlled oscillation unit has a surface acoustic wave oscillator, the digital value storage unit has an A/D converter and a memory, and the sample holding unit has a D/A converter, a capacitor and an analog switch interposed between the D/A converter and the capacitor, and

wherein the digital value stored in the digital value storage unit is obtained by filtering the phase difference signal by using a low pass filter.

2. The oscillation device of claim 1 , wherein the control unit further performs the step of intermittently stopping the operations of the voltage-controlled oscillation unit and the sample holding unit after the step of stopping the reference oscillation unit, the phase comparing unit and the digital value storage unit

3. The oscillation device of claim 2 , wherein the control unit performs the step employing as the control voltage the phase difference signal when the step of intermittently stopping the operations of the voltage-controlled oscillation unit and the sample holding unit is performed a determined number of times.

4. The oscillation device of claim 1 , wherein when a specific oscillation time elapses, the control unit performs the step of stopping the operations of the voltage-controlled oscillation unit and the sample holding unit, after the step of stopping the reference oscillation unit, the phase comparing unit and the digital value storage unit, and

wherein when a specific waiting time elapses after stopping the operations of the voltage-controlled oscillation unit and the sample holding unit, the control unit performs one of the steps of employing as the control voltage the phase difference signal, and employing as the control voltage the hold signal.

5. A method for controlling an oscillation device including a reference oscillation unit for generating an oscillating signal of a specific frequency, a voltage-controlled oscillation unit for generating an output oscillation signal whose frequency is dependent on a control voltage, and a phase comparing unit for detecting a phase difference based on the oscillating signal and the output oscillation signal, the method comprising the steps of:

(a) operating the voltage-controlled oscillation unit until a specific time elapses or until the phase difference becomes within a specific range by using a phase difference signal corresponding to a phase signal as the control voltage;

(b) storing the phase difference signal as a digital value;

(c) intermittently renewing and maintaining a hold signal in accordance with the digital value; and

(d) operating the voltage-controlled oscillation unit by using the hold signal as the control voltage,

wherein the steps (c) and (d) are repeated alternately,

wherein the reference oscillation unit and the phase comparing unit are stopped when the step (c) or (d) is performed, and

wherein the step (c) is performed by a sample holding unit having a D/A converter, a capacitor and an analog switch interposed between the D/A converter and the capacitor.

6. The method of claim 5 , further comprising, after the step (d), the step of:

(e) stopping the operation of the voltage-controlled oscillation unit,

wherein the steps (c) to (e) are repeated sequentially.

7. The method of claim 6 , wherein the steps (a) and (b) is performed after the steps (c) to (e) are sequentially repeated a determined number of times.