Patent ID: 7978984

Claim:
A data communication unit using a light-emitting diode for data communication, comprising: a light-emitting diode outputting light when a current flows therethrough; a transmission circuit applying a forward bias to said light-emitting diode based on transmission data; and a separation circuit outputting a first voltage that changes according to a second voltage which is generated in said light-emitting diode when the forward bias is not applied to said light-emitting diode, wherein said transmission circuit causes said light-emitting diode to transmit optical transmission data, and said separation circuit takes out the voltage generated in said light-emitting diode, as data, and wherein said separation circuit includes means for separating data having different frequency from a pulse frequency of optical data transmitting from said transmission circuit wherein said transmission circuit has a PNP transistor having a base node connected to a cathode node of said light-emitting diode and has a collector node connected to an anode node of said light-emitting diode, and when applying the forward bias to said light-emitting diode, said transmission circuit controls potentials of said cathode node of said light-emitting diode and said base node of said PNP transistor to a value lower than a voltage of an emitter node of said PNP transistor, thereby turning on said PNP transistor, and wherein said separation circuit is connected to said anode node of said light-emitting diode.