| 摘要 |
PURPOSE:To control an optical output so that high and low level of the output are always constant by supplying a bias current to a semiconductor laser by the output of an LPF2 interrupting the output high frequency of an operational amplifier circuit. CONSTITUTION:A pulse current 18 is monitored by a monitor resistor 9, a voltage across the monitor resistor 9 is received by buffers 67, 68 having a high input impedance and the result is subjected to differential amplification by a differential amplifier circuit comprising an operational amplifier 73 and resistors 69-72. The output of the differential amplifier circuit is given to LPFs 11, 12 to obtain a pulse current monitor signal 15. In case of read, since no pulse current is conducted and the pulse current monitor signal 15 is zero. The LPFs 2, 6 are constituted by the resistor 45 and the capacitor 46 of feedback path of the operational amplifier 47 and a transistor 48 and the resistor 49 constitute a bias current driving circuit 7, from which a bias current depending on the output of the operational amplifier 78 is fed to a semiconductor laser 1. Thus, the bias current is controlled so as to make the high/low level of the optical output always constant. |
