Opical coupling circuit including a light-receiving unit provided not to receive optical signal, and signal processing device

A light-receiving apparatus of an optical coupling circuit, comprising:

• a first light-receiving device that outputs an optical current according to the optical signal;
• a second light-receiving device that is provided not to receive the optical signal;
• a current duplication circuit that duplicates a current flowing through the second light-receiving device;
• a current-voltage conversion circuit that converts a current, which is generated by subtracting the current duplicated by the current duplication circuit from a current flowing through the first light-receiving device, into a voltage signal;
• and
• a comparator that output a result of a comparison between the voltage signal converted by the current-voltage conversion circuit and a threshold voltage as the output signal,
• wherein the first light-receiving device and the second light-receiving device are electrically insulated from a light-emitting unit that outputs an optical signal corresponding to an input electric-signal.

A signal processing apparatus, comprising:

• a signal generation unit that outputs an output electric signal according to an input electric signal;
• and
• an optical coupling circuit to which an electric signal is applied, an input and an output thereof are electrically insulated;
• wherein
• the optical coupling circuit is inserted one or both of a path through which the input electric signal is input to the signal generation unit and a path through which the output electric signal is output from the signal generation unit;
• the optical coupling circuit comprises;
• a light-emitting unit that outputs an optical signal corresponding to an input electric signal;
• and
• a light-receiving unit that is electrically insulated from the light-emitting unit and outputs an electric signal according to the received optical signal as an output signal,
• the light-receiving unit comprises;
• a first light-receiving device that outputs an optical current according to the optical signal;
• a second light-receiving device that is provided not to receive the optical signal;
• a current duplication circuit that duplicates a current flowing through the second light-receiving device;
• a current-voltage conversion circuit that converts a current, which is generated by subtracting the current duplicated by the current duplication circuit from a current flowing through the first light-receiving device, into a voltage signal;
• and
• a comparator that output a result of a comparison between the voltage signal converted by the current-voltage conversion circuit and a threshold voltage as the output signal.