| 摘要 |
PURPOSE:To increase the minimum receiving level and to remove malfunction at the variation of power supply voltage and temperature by changing the clamping level of a threshold voltage similarly to the operation point of an amplifier at the variation of the power supply voltage and temperature. CONSTITUTION:A digital signal obtained by converting an optical signal into an electric signal by a photodetector 1 in an optical receiver is amplified by an amplifier 2 and its output is inputted to a threshold setting circuit 3 and one input of a comparator 4. A photodetector 5 converts DC light obtained from a light emitting element 8 to be emitted by a driving circuit 7 into a digital signal and applies the digital signal to the setting circuit 3 through an amplifier 6. A distance between the light emitting element 8 and the photodetecting element 6 or the output power of the light emitting element 8 is set up to set up the signal amplified by the amplifier 6 slightly larger than the signal amplified by the amplifier 2. The clamping level of the threshold voltage of the comparator 4 is set up in a setting circuit 3 so as to be changed similarly to the variation of the power supply voltage and temperature. Thus, the minimum receiving level is prevented from being increased and the device is prevented from malfunction. |
