| 摘要 |
A light receiving circuit provided with an amplifier for amplifying an output signal of a semiconductor light receiving element is disclosed. The amplified electrical signal is first inputted to the inverting input terminal of a comparator. An output voltage of the comparator is divided by resistors connected in series with each other. The difference voltage between the voltage applied to the inverting input terminal and a voltage being present at a connection point between the resistors is divided by means of resistors, and a voltage obtained by this voltage division is then applied to the non-inverting input terminal of the comparator. The amplitude of an output voltage of the comparator is reduced by dividing this output voltage. Moreover, the mean value of this output voltage thereof can be made to be closer to the ground potential. Therefore, when the output of the comparator has a high level, a threshold voltage to be applied to the non-inverting input terminal becomes lower. Consequently, the minimum receiving level of a received optical signal can be lowered.
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