| 摘要 |
PURPOSE:To realize a high-speed modulation by a method wherein a field-effect transistor is connected in parallel with an LED and the field-effect transistor is turned on and off by using a digital signal for modulation use so that an electric charge accumulated in the LED during a light-emitting operation can be discharged quickly at an extinction. CONSTITUTION:When a digital signal of a voltage Vin is applied to a gate of a field-effect transistor 7 from an input terminal 5, the voltage Vin is turned to a high level; when a part between a source and a drain of the field-effect transistor 7 is set to an OFF state, an electric current from a constant-current source 3 flows to an LED 4; the LED 4 is set to a light-emitting state. Then, the voltage Vin is turned to a low level; when the part between the source and the drain of the field-effect transistor 7 is set to an ON state, the electric current from the whole constant-current source 3 flows through the field-effect transistor 7; the LED 4 is set to an extinction state. During this process, an electric charge which has been accumulated in the LED 4 is discharged instantaneously because the part between the source and the drain of the field-effect transistor 7 is short-circuited. Thereby, a high-speed modulation can be executed. |
