| 摘要 |
PURPOSE:To increase the margin of the code error for the control of the identifier threshold level of the optical reception circuit which applies the AGC system to control the bias of APD (Avalanche Photo Diode), by varying the threshold level when the optical input level exceeds the fixed level. CONSTITUTION:The optical signal supplied to the optical reception circuit is turned into the electric signal through photoelectric converter 1 and then applied to identifier 6 via DC regeneration circuit 4, equalizer 5 and others after receiving amplification through preamplifier 2 and main amplifier 3 each. Part of the output of equalizer 5 is applied to peak detector 7. With this output, bias control circuit 8 gives the control to the bias of APD. The output of circuit 8 is applied to reception level monitor circuit 10, and the output of circuit 10 is applied to threshold level circuit 11. This output is detected when the optical input level exceeds the fixed level to vary the threshold level of identifier 6. |
