| 摘要 |
In a light-receiving circuit 31 of an optical coupling device in which a dummy photodiode D2 is provided in a vicinity of a photodiode D1, and their outputs from current-to-voltage converting amplifiers A1 and A2 are compared with each other and subjected to waveform shaping by a hysteresis comparator 33 for improving a common mode rejection ratio, negative feedback circuits of the amplifiers A1 and A2 include impedance variable circuits Z1 and Z2 in which impedances decrease as a level of an inputted photoelectric current Ipd increases. Therefore, an increase of the current Ipd decreases gains of the amplifiers A1 and A2 and thus narrows a band, whereas a decrease of the current Ipd increases the gains and thus widens the band. This minimizes pulse width distortion caused by quantity changes of incoming light, thereby realizing a high-speed transmission rate.
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