| 摘要 |
PURPOSE:To prevent the disconnection of a word beginning by differential- amplifying the rectifying/smoothing output of a transmitting/receiving output that is transmitted/received and shortenning the transmission keeping time of a word ending disconnection preventing circuit by differential-amplified output corresponding with the input of a receiving. CONSTITUTION:A transmitting input through a microphone 1 is discriminated by the comparison of the transmitting/receiving level at a comparison control circuit 13a, and each loss of variable loss circuits 3 and 8 is set as slight and bigger and the amplifying state of an amplification means is switched to a transmitting state. Next, even when the transmitting input becomes smaller, the transmitting state is kept during a specified time that is set up by the time constant of a charging/discharging circuit and the disconnection of the word ending. On the other hand, when the receiving is inputted during the transmitting keeping period, the output of a differential amplifier circuit 22 of a word disconnection preventing circuit 23 becomes greater and a receiving detecting signal is outputted and thereby, the transmitting keeping period of the word ending disconnection preventing circuit is shortened and the disconnection of the word beginning of a receiving signal is prevented.
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