| 发明名称 |
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| 摘要 |
PURPOSE:To detect a pilot signal level by allowing a control circuit to lower the bias voltage of a photodetector when a level detection circuit detects a faulty output level so as to restore a preamplifier to the normal state. CONSTITUTION:Since no output signal is given from a comparator 17 in the normal state where the output signal of the preamplifier 2 is not a V'ref or below, a comparator 20 controls a bias voltage generating circuit 7 controlling the bias voltage of an APD 1 based on the output signal of a comparator 14. When the output voltage of the preamplifier 2 reaches the voltage V'ref or below, a constant voltage is fed to one terminal of a comparator 20 to reduce forcibly the amplification factor of the APD 1, then a bias voltage level outputted from a bias voltage generating circuit 7 is lowered. A pilot signal level being the output of a band pass filter 11 is detected at a point of time when the preamplifier 2 starts its operation normally through the reduction in the amplification factor of the APD 1. |
| 申请公布号 |
JPH0628348(B2) |
申请公布日期 |
1994.04.13 |
| 申请号 |
JP19860043321 |
申请日期 |
1986.02.28 |
| 申请人 |
FUJITSU KK;NIPPON DENSHIN DENWA KK |
发明人 |
HANAOKA SUSUMU;FUKUGAHARA TSUTOMU;TAKAHASHI MASAAKI;SHUDO KOICHI |
| 分类号 |
H04B10/60;H03F3/08;H03G3/20;H04B10/00;H04B10/07;H04B10/293;H04B10/40;H04B10/50;H04B10/564;H04B10/572;H04B10/67;H04B10/69 |
主分类号 |
H04B10/60 |
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