| 摘要 |
PURPOSE:To simplify the mounting of a laser diode, by satisfying speicific relation between the resistance between the transistor provided to the side not driving the laser diode of a diferential type transistor driving circuit and ground, the resistance between the output side of a second constant current circuit and said resistance and the resistance between the impedance of a coaxial cable and the terminal of a measuring instrument. CONSTITUTION:A differential transistor circuit constituted of transistor TR2, TR3 supplies the current of a constant current circuit CCs to a laser diode LD and a resistor R4. A constant current circut CCm constituted of an operator amplifier A2, a transistor TR4 and a resistor R6 supplies a current IBM proportional to the bias current IB of the laser diode LD to the resistor R4 and a resistor R5. A resistor R7 supplies monitor voltage Vm to a terminal resistor Rt through an output terminal CN and a coaxial cable CX. Subsequently, when the value of the resistor R6 is set to (a)-times of the value of resistor R1 and the resistors R4, R5, R7, Rt and the characteristic of the coaxial cable are set to formula, the voltage Vm is proportional to the sum of the bias current IB and a signal current IS.
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