Patent ID: 6954123

Claim:
A tuning circuit comprising a series resonance circuit, a driving circuit connected to a terminal of the series resonance circuit and a negative resistance circuit connected to other terminal thereof; said negative resistance circuit including a collector-emitter dividing type amplifying circuit constituted by a first transistor, an emitter earth type amplifying circuit constituted by a second transistor and connected to the collector-emitter dividing type amplifying circuit, a positive feedback circuit for positively feeding back an output of the emitter earth type amplifying circuit to the collector-emitter dividing type amplifying circuit and a negative feedback circuit for negatively feeding back an output of the emitter earth type amplifying circuit to the collector-emitter dividing type amplifying circuit, the other terminal of the series resonance circuit being connected to an input of the collector-emitter dividing type amplifying circuit and an output of the emitter earth type amplifying circuit being taken out as an output of the negative resistance circuit.