Patent ID: 8139953

Claim:
A signal transmission device that transmits, in form of an optical signal, multivalued data, which shifts through three or more plurality of logical values, comprising: a light emitting element that outputs light having an intensity corresponding to a power supply current supplied thereto; a current source that is capable of supplying the light emitting element with the power supply current, which has a plurality of current values corresponding to the plurality of values through which the multivalued data shifts; and a modulating section that modulates current value of the power supply current supplied from the current source, in response to a shift of the multivalued data, wherein the optical signal carrying the multivalued data is generated from an input digital value represented by multiple bits, the current source includes a number of bit current sources corresponding to a number of the bits representing the digital value; each of the bit current sources generates a current corresponding to a bit position of the bit of the digital value that corresponds thereto, the modulating section includes a number of current control switches corresponding to the number of the bits of the digital value, such that the current control switches correspond to the bit current sources, respectively; and each of the current control switches between supplying and not supplying the light emitting element with the current generated by the bit current source corresponding thereto, in response to a logical value taken by the bit of the digital value corresponding thereto, the signal transmission device further comprising: a measuring section that measures power supply current—output intensity characteristic of the light emitting element; and a current control section that controls current value of the power supply current generated by each of the bit current sources, based on the power supply current—output intensity characteristic.