| 摘要 |
PURPOSE:To make operation of a sound volume switch circuit stable to the reception input in a low level, by providing non-linear characteristic for an input and output characteristic of a transmission rectifying and smoothing circuit, in a loudspeaker telephone set having the sound volume switch circuit. CONSTITUTION:An audio signal for transmission and reception is rectified and smoothed with a transmission and reception rectifying and smoothing circuits 10 and 11, the output of the circuits 10 and 11 is compared to operate and a sound volume switch circuit 3. A non-linearity characteristic is given to the input and output characteristic of the circuit 11 so that the output to an input of low level can be suppressed with the input and output characteristic of the circuit 11. Without giving the effect on the operation of the circuit 3 with a normal volume signal, the interruption of reception caused by surrounding noise can be reduced at the reception input of low level, allowing to operate the sound volume switch circuit stably. |
