Patent ID: 7209668

Claim:
A data transmission apparatus for performing data communication based on optical transmission, comprising: a transmitting unit for converting and sending electric communication data to be transmitted into optical communication data; a photoelectric conversion circuit for receiving said optical communication data and converting said received optical communication data into received electric communication data; and a variable setting unit for setting said photoelectric conversion circuit to generate received electric communication data in response to an input level of said received optical communication data, wherein said photoelectric conversion circuit comprises: a light receiving unit for generating a current based on said received optical communication data; and a signal generating unit for generating said received electric communication data based on said current generated by said light receiving unit, a comparator for comparing a current, the value of which indicates a magnitude of said current generated by said light receiving unit, with a reference current, and for generating said received electric communication data, and wherein said variable setting unit comprises a variable current supply for setting said photoelectric conversion circuit by adding a predetermined current to said reference current or by subtracting a predetermined current from the current, the value of which indicates the magnitude of said current generated by said light receiving unit, wherein said optical communication data is digital data, and said variable current supply subtracts a current value, which is substantially half said current generated by said light receiving unit when said optical communication data indicates H logic, from said current value generated by said light receiving unit.