Patent ID: 8149069

Claim:
A voltage-controlled oscillating circuit comprising: a driving transistor including an emitter to which a power source voltage is supplied through a first resistor and a base to which a voltage obtained by dividing the power source voltage is applied; an oscillating transistor including a base connected to a collector of the driving transistor to perform an oscillating operation; a filter circuit into which an output from a collector of the oscillating transistor is branched and input and which limits the band of the output to return the output to the base of the oscillating transistor, thereby regulating the voltage supplied to the base by a control voltage from the outside; and a buffer amplifier which amplifies the output from the collector of the oscillating transistor, wherein the base of the driving transistor is connected to one end of a first capacitor having the other end connected to ground, a transistor having a direct-current amplification factor smaller than that of a usual driving transistor is used as the driving transistor, the emitter of the driving transistor is connected to the collector of the oscillating transistor via a second resistor and a first coil which are connected in parallel, and an emitter of the oscillating transistor is connected to one end of a second coil having the other end connected to the ground.