Patent ID: 7868705
Filing Date: 2011-01-11
Classification: H03B

Abstract:
1. A high-frequency oscillator, comprising: first and second resonance circuits that resonate at frequencies different from each other; a first amplifier circuit that is connected to the first resonance circuit and amplifies a first resonance signal output from the first resonance circuit; a second amplifier circuit that is connected to the second resonance circuit and amplifies a second resonance signal output from the second resonance circuit; a selection circuit that is connected to the first and second amplifier circuits and that selectively operates a respective one of the first and second amplifier circuits; a grounded capacitor that is connected to the first and second amplifier circuits and is commonly used by the first and second amplifier circuits; an auxiliary grounded capacitor; and a buffer circuit that is commonly connected to the first and second amplifier circuits, and that amplifies a signal output from each of the first and second amplifier circuits; wherein the auxiliary grounded capacitor is connected in parallel to the grounded capacitor when a respective one of the first and second amplifier circuits operates; the auxiliary grounded capacitor is disconnected from the grounded capacitor when a respective other one of the first and second amplifier circuits operates; the first amplifier circuit includes a first bipolar transistor having a base terminal connected to a power source terminal through a first bias resistor; the second amplifier circuit includes a second bipolar transistor having a base terminal connected to the power source terminal through a second bias resistor; the selection circuit includes: at least one of the first and second switch circuits is arranged between the power source terminal, and a corresponding at least one of the first and second bias resistors of the first and second bipolar transistors in which the operation status of the first and second bipolar transistors is switched by the at least one of the first and second switch circuits; the grounded capacitor is connected between the power source terminal and the at least one of the first and second switch circuits; the auxiliary grounded capacitor is connected between at least one of the first and second switch circuits and a corresponding at least one of the first and second bias resistors; the buffer circuit includes a third bipolar transistor; an emitter terminal of the third bipolar transistor included in the buffer circuit is cascade-connected to collector terminals of the first and second bipolar transistors; and one of the first and second switch circuits to which the auxiliary grounded capacitor is connected, is connected to the emitter terminal of the third bipolar transistor included in the buffer circuit.