| 摘要 |
PROBLEM TO BE SOLVED: To provide a voltage-controlled oscillator having a large variable amplitude of an oscillation frequency, while assuring the oscillation starting properties. SOLUTION: An oscillation signal becomes a predetermined amplitude value by a detecting circuit OPC. A transfer of an oscillation operation from an initial state to an ordinary state is detected to turn on a P-channel MOS transistor Tr, and hence a capacitor CA is connected, in series with a series circuit having a crystal oscillator XL and a varicap diode CV. In the initial state, a load capacitor is reduced to cancel the reduced part of a conductance gm of an oscillation amplifier, corresponding to an amplitude reduction of the crystal oscillator. A negative resistance necessary to maintain proper oscillation starting properties is obtained. In the normal state, the effect of the varicap diode CV is increased, to increase the change in the amplitude of an oscillation frequency.
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