| 摘要 |
PURPOSE:To prevent howling by providing attenuator circuits after an amplifier, which amplifies the output of a microphone, and an amplifier, which amplifies receiving signals, respectively and oerating these attenuator circuits alternately at a transmission time and a receiving time. CONSTITUTION:Service loss circuit 3 is provided in the output side of transmission amplifier 1 which amplifies the output of microphone 2, and receiving loss circuit 4 is provided in the input side of rceiving amplifier 5 where receiving signals from the telephone line are inputted, and the output side of amplifier 5 is connected to speaker 6. Further, comparator 7 which controls loss circuits 3 and 4 to operate them alternately is provided, and transmission auxiliary loss circuit 9 and receiving auxiliary loss circuit 8 where output of amplifiers 1 and 5 are inputted through time constant circuits 11 and 10 are connected to this comparator 7, thereby making it possible to control loss circuits 3 and 4 by the control of comparator 7. |
