| 摘要 |
PURPOSE:To supply electric current stably to a laser diode while switching it at a high speed, by utilizing the laser diode and an impedance element as loads having equivalent characteristics and altenately switching the loads according to a two-value driving signal so as to connect it to a constant current source. CONSTITUTION:A diode 1 is supplied by a constant current source 3 and connected in series to a transistor Tr7. A signal Vin is applied to the base thereof through an inverter 10. When the signal Vin is 'H', the diode 1 emits light. A transistor 8 is supplied by the constant current source 3 in common with the diode 1 and a voltage drop thereof is determined by a constant voltage V1 at a level equal to that of the diode 1 during operation. A transistor Tr9 has characteristics similar to those of the transistor Tr7 and is connected in series to the Tr8. A signal Vin is applied to the base of the Tr9 so that the Tr8 is operated as a load of the constant current source when the signal Vin is 'H'. Accordingly, since the constant current source supplies current to equivalent loads regardless the diode is ON or OFF, a potential across the load is, not varied and the diode can be switched at a high speed. |
