| 摘要 |
PURPOSE:To prevent the variation in output due to difference in FET characteristics such as a pinch-off voltage or transconductance and to enable a laser diode to have high-speed, stable and high output, by providing an amplitude variable amplifier circuit in the step prior to an FET circuit for supplying pulse current to the laser diode. CONSTITUTION:A minimum value of input signals is fixed to an FET pinch-off voltage by a clamp circuit 14 or the like. An input signal to an FET driving circuit 13 is previously changed in amplitude as required by an amplitude variable circuit 15 before its supplied to an ON/OFF FET gate electrode. According to this construction, if the inclination of a characteristic curve is gentle and an output current is low, the input signal can be amplified and supplied to the FET circuit 13 for providing higher output current Ip. If the inclination is steep and the output current is low, the amplification factor can be decreased for limiting the output current. Further, by amplifying the input signal, driving current can be generated, avoiding the curved portion in the characteristic curve close to the FET pinch-off point. Thus, a circuit capable of turning the emission of a laser diode ON and OFF correctly and reliably can be realized. |
