| 摘要 |
PROBLEM TO BE SOLVED: To eliminate generation of noise of an echo phenomenon or the like and to perform smooth communication without giving an unpleasant feeling to a telephone side transmitter by turning OFF the transmission of microphone voice signals in the case that the voice signals of a speaker are larger than a prescribed set value. SOLUTION: A level detection part 21 provided in a general telephone voice transmission circuit 17 detects the level of voice signals S1, outputs level detection signals S3 and supplies them to a switch part 22 provided in a microphone voice signal transmission circuit 20. When the transmitter utters a loud voice, the level of the telephone voice signals S1 becomes high and the voice level of the speaker 16 becomes higher than the set value, by the detection signals S3, the switch part 22 is turned OFF and the voice signals S2 from a microphone 19 are interrupted and prevented from being inputted to a portable telephone 12. Thus, the generation of the echo phenomenon is prevented. Also, switching sound noise accompanying the ON/OFF of the switch part 22 is suppressed by providing a buffer circuit by a resistor and a capacitor in a level detection signal transmission line 31. |
