| 摘要 |
PURPOSE:To prevent a unit, equipped with an optical transmitting means including a light emitting element and an optical receiving means including a light receiving element, from causing a communication error even if the source voltage varies or if the distance between transmission and reception becomes long and to improve the reliability by performing constant-current control over a current for making the light emitting element illuminate at the time of transmission. CONSTITUTION:The optical transmission means consists of a communication control LSI 1, a buffer 2, an operational amplifier 3, a transistor(TR) 4, the light emitting element 5, and a Zener diode 6. Then the operational amplifier 3 is provided between the base and emitter of the TR 4 which drives the light emitting element 5 to constitute a constant-current circuit which makes the photocurrent, flowing to the light emitting element 5, constant by providing negative feedback. Namely, the constant- current control over the current making the light emitting element 5 illuminate is performed at the time of transmission, so even if the source voltage VCC varies, the light output of the light emitting element 5 becomes constant. Further, the output voltage of the light receiving element is compared with a reference voltage which is made constant and data are outputted. Therefore, even if the source voltage VCC varies, the data which are reproduced have no variation. |
