| 摘要 |
PROBLEM TO BE SOLVED: To provide stable operation by a single transducer by grounding first and second output circuits of a branching circuit for branching a reception signal and connecting it to first and second input terminals of a differential amplifier through a resistance and a transducer, connecting them to the second terminal by way of the first terminal and the resistance and giving input signals of the first and second terminals the same amplitude. SOLUTION: A full duplex audio communication circuit 1 amplifies a reception signal R from a communication device body 200 at operational amplifying circuits 5 and 6, acoustic outputs at a transducer 10 through a second output circuit 11b of a branching circuit 11 and, at the same time, outputs to a second input terminal 9b of a differential amplifying circuit 9 through the second output circuit 11b and a resistance. A first input terminal 9a is outputted to through a first output circuit 11a. Here, resistance values of the first and second output circuits 11a and 11b are determined so that amplitudes of input signals of the first and second input terminals 9a and 9b of the differential amplifier 9 are made to be the same and an output of the differential amplifier 9 by the reception signal R is made 0.
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