AGC CIRCUIT IN OPTICAL DUPLEX COMMUNICATION

摘要

PURPOSE:To realize the stable AGC circuit operation by selecting a capacitor or a DC power supply. CONSTITUTION:A gain of a gain variable element 3 is changed by a voltage Vc of a capacitor 12 or a battery voltage Vb. The capacitor 12 is charged by a signal level detected by a level detection circuit 10. A switch 11 is operated by a control signal from a control circuit 5 and thrown to the position B at transmission and thrown A at reception. The voltage Vb is a constant DC voltage generated by a DC power supply such as a battery and reduces the gain of the gain variable element 3 sufficiently. At the reception of an optical input, a control voltage in response to the detection level is stored in the capacitor 12 and held even for a transmission period. Furthermore, the voltage Vb is selected by the switch 11 at the transmission and the transmission signal is outputted from the gain variable element 3 subject to AGC with a low gain. On the other hand, the reception signal is made constant by the AGC.