Patent ID: 6728494
Filing Date: 2004-04-27
Classification: H04B

Abstract:
A circuit that drives a light-emitting device based on an inputted digital signal, said circuit comprising:an npn transistor, supplied at a base thereof with an electrical signal corresponding to said digital signal, for outputting a voltage at a high or low level to an emitter thereof based on the electrical signal; a current compensation circuit, connected to the emitter of said transistor, for compensating an output current of a collector of said transistor at a rising edge when an emitter voltage of said transistor is at the high level, and compensating the output current at a falling edge when the emitter voltage of said transistor is at the low level; a signal current source, connected to the collector of said transistor, for amplifying said output current by a predetermined multiplication factor, and outputting a signal current; a constant-current source, connected to said signal current source in serial, for diverting a part of direct current components of said signal current outputted from said signal current source; and a light-emitting device, connected to said signal current source in serial and to said constant-current source in parallel and supplied with an injection current obtained by subtracting the diverted part from said signal current, for emitting light based on the injection current.