| 摘要 |
PURPOSE:To prevent word end and word top signals from being cut by providing a time constant variable circuit for changing discharging and charging time constants of the smoothing capacitor of each rectifying and smoothing circuit and controlling the circuit in accordance with the mutual level between transmission and reception call levels. CONSTITUTION:The transmission input of the rectifying and smoothning circuit 6 is rectified by a diode 30 and charges the capacitor 32. Then the transmission call level of the output terminal C of the circuit becomes high. As a result, the output of a comparator 13 comes to 'L' level, and losses of variable loss circuits 3 and 8 are brought into the low and high transmission call states, respectively. Then a point switching from a transmission call to a reception one is delayed, and the word end cutting of the transmission call signal can be prevented. On the other hand, when the reception input of the rectifying and smoothing circuit 12 is increased to raise the reception call level of an output terminal D, an analog switch 35a controlled throught inverters 39a, 39b and 39c is turned off, the charging time and discharging time of the capacitor 32 of the circuit 6 become longer and shorter, respectively. Accordingly the point when the transmission call is switched to the call receiving state is advanced, whereby the word top cutting of the reception call signal can be prevented.
|
