| 摘要 |
PURPOSE:To prevent malfunction and to keep the naturality of talking by providing a circuit detecting a change in a transmission signal in a voice switch circuit for a loudspeaker telephone set. CONSTITUTION:A circuit 12 detecting the change in the transmission signal is provided to a detection circuit of a transmission line so as to detect whether or not an output of a transmission signal rectifying smoothing circuit 8 is attenuated timewise. In case of the talking voice uttered from a talker, the transmission signal level is increased, but in case of a reception echo sound amplified by a speaker 7, the transmission signal level is attenuated. When the voice switch is in the reception state, even when the output level of the transmission signal rectifying smoothing circuit 8 is larger than the output level of a reception signal rectifier smoothing circuit 9, if the transmission signal change is attenuated, the transmission signal is discriminated as the reception echo sound amplified by the speaker 7 to inhibit the transition to the transmission state. |
