| 摘要 |
PURPOSE:To operate a laser diode driving circuit by a positive power, to be easily matched to a TTL circuit and to operate it at a high speed by connecting a constant-current circuit having a current value larger than the threshold current of a laser diode in series with the diode, and further connecting a branch circuit for branching part of the current of the circuit in response to a modulation signal in parallel. CONSTITUTION:A constant-current circuit 18 has an LD current control voltage input terminal 3, resistors 8, 13, 16, a P-N-P transistor 9, N-P-N transistors 10, 15, a diode 14, and a capacitor 17. The circuit 18 is connected directly or through a level shift diode 11 in series with a laser diode 12, and a branch circuit formed of an N-P-N transistor 6 and a resistor 7 is connected in parallel with the series circuit, when the potential of a reference voltage input terminal 2 is lower than a signal input terminal 1, the transistor 6 becomes 'OFF', and a current I all flows in the diode 12. When the potential of the terminal 2 is higher than the terminal 1, the transistor 6 becomes 'ON', a constant current 14 flows in the transistor 6, and only a constant current Ith flows to the diode. |
