Patent ID: 8847140

Claim:
A light receiving circuit comprising: a photodiode for converting a light signal into an electric signal, having one end connected to a first potential line and the other end connected to a first internal terminal; a transimpedance amp having a feedback resistor with one end connected to the first internal terminal, a first MOS transistor of a first electric conduction type with a gate connected to the first internal terminal and a drain connected to a second internal terminal, and a first constant electric current source connected between the second internal terminal and a second potential line; an electric current comparator having a second MOS transistor of the first electric conduction type with a drain connected to an output terminal, a source connected to the first potential line, and a gate connected to the second internal terminal, and a second constant electric current source connected between the output terminal and the second potential line; and an automatic threshold control circuit having a current mirror circuit for forming an electric current flowing between the second potential line and a first connection point, and allowing an electric current to flow between the second potential line and a second connection point connected to the output terminal, a third constant electric current source with one end connected to the second potential line and the other end connected to the first connection point, and a third MOS transistor of the first electric conduction type with a drain connected to the first connection point, a source connected to the first potential line, and a gate connected to the second internal terminal.