PURPOSE: To prevent the disconnection of the word ending in a transmitting signal and that of the word beginning in a receiving signal by providing a word beginning disconnection preventing circuit in the receiving input, altering the discharge characteristic of a word ending disconnection preventing circuit according to the output of a differential amplifier and switching an amplification means.
CONSTITUTION: A differential amplifier circuit 13a outputs a differential amplifier signal between a transmitting level signal and a receiving level signal and by this output, a capacitor 22 is charged rapidly through a diode 20 and a resistor 23 and is discharged gradually through a resistor 23. The charging potential of this capacitor 22 is also discharged through a resistor 30 because a switch 29 is set as on when the receiving input detection signal of a detection circuit 27 is obtained by providing a word beginning disconnection preventing circuit 28 and the resistor 30 is connected in parallel with the diode 20, and the discharging time constant of the capacitor is shortened. Thereby, varible loss circuits 3 and 8 are switched from a transmitting state to a receiving state rapidly according to the output of the circuit 13a in a presence of the receiving input and the elimination of the word beginning disconnection of the receiving signal makes a natural conversation.
FUKAGAWA HITOSHI
TAKEHARA KIYOTAKA
KINEKAWA YASUKAZU
