Patent ID: 7880129

Claim:
A light receiving circuit comprising: a converting unit that converts an optical signal into an electric signal; a measuring unit that measures a specified physical quantity of the optical signal; a generating unit that binarizes a signal level of the electrical signal into a first value or a second value based on a specified threshold and generates a data signal that indicates a binarized value; a ratio acquiring unit that calculates a ratio of a period in which the first value is indicated by the data signal generated by the generating unit to a period in which the second value is indicated thereby; a threshold setting unit that sets the threshold; a storing unit that in advance stores information on a relationship among the physical quantity measured by the measuring unit, the ratio calculated by the ratio acquiring unit, and a bit error rate of the data signal generated by the generating unit; and a control unit that controls the threshold setting unit to change the threshold based on the information stored in the storing unit, the physical quantity measured by the measuring unit, and the ratio calculated by the ratio acquiring unit so that the bit error rate of the data signal generated by the generating unit is low.