Patent ID: 8791442

Claim:
An optical coupling device, comprising: a light emitting element; a first photodiode having a cathode and an anode to be connected to a power source on a lower potential side, the first photodiode receiving an optical signal generated by the light emitting element and converting the optical signal into a first electrical signal; a first inverting amplifier which is provided with input and output ends, and a first feedback resistor and a first operating amplifier connected in parallel with each other, the input end being connected to the cathode of the first photodiode, the first inverting amplifier outputting a first signal obtained by inverting the first electrical signal, from the output end; a second photodiode having a cathode and an anode which is connected to the power source on a lower potential side; a second inverting amplifier which is provided with input and output ends, and a second feedback resistor and a second operating amplifier connected in parallel with each other, the input end of the second inverting amplifier being connected to the cathode of the second photodiode, the second inverting amplifier outputting a second signal from the output end; and a comparator which receives the first and second signals and compares the first and second signals using the second signal as a reference voltage to output a comparison amplified signal, wherein the product of a first junction capacitance of the first photodiode and a resistance of the first feedback resistor, and the product of a second junction capacitance of the second photodiode and a resistance of the second feedback resistor are set to be the same value substantially, and the second junction capacitance is set to be smaller than the first junction capacitance.