| 摘要 |
PURPOSE: To provide an automatic gain circuit for optical receiver for which high-speed property and stability are secured. CONSTITUTION: An optical input terminal 10 is connected to an ADP 2, and the output part of the ADP 2 is connected to the input part of a preamplifier 3. The output part of the preamplifier 3 is connected to the input part of a variable gain amplifier 4. The output part of the variable gain amplifier 4 is connected to an output terminal 11 and the input part of a peak detector 5. The output part of the peak detector 5 is connected to the control input part of the variable gain amplifier 4 and connected through a time constant circuit 6 to the input part of a DC amplifier 7. The output part of the DC amplifier 7 is connected to the input part of an HV circuit 8. The output part of the HV circuit 8 is connected through an automatic time constant circuit 9 to the ADP 2. Therefore, a time constant is changed corresponding to a voltage from the HV circuit 8 of the automatic time constant circuit 9, and an inverse bias is impressed to the ADP 2. Thus, an amplification factor M of the ADP 2 is changed and the amplitude of a signal at the output terminal 11 is kept constant. |
