| 摘要 |
PURPOSE:To stabilize the optical output regardless of the speed of transmission data, the mark ratio, on and off, etc., by a simple low frequency circuit by controlling the peak level and the low level of the optical output of a light emitting element in a DC manner. CONSTITUTION:The voltage at the end of a detection resistor R1 is a constant Dc voltage regardless of the mark ratio of transmission data or the fluctuation and others such as on/off of the transmission data, etc., and an error signal, which is gotten by being compared with the reference voltage Vref1 by an error amplifier 1, is applied to a transistor Q3 so as to control an amplitude current IP. On the other hand, three low-level currents IB are generated by transistors Q4, Q5, and Q6, and the low-level current of the transistor Q4 is supplied to a light emitting element LD1, and the low- level current of the transistor Q3 is supplied to a light emitting element LD2. Moreover, the low-level current of the transistor Q6 is supplied to a light emitting element LD3. Since the values of three low-level currents IB are well even, the optical output of the light emitting element LD3 can be used as the optical output corresponding to the low-level current values of the light emitting elements LD1 and LD2, and it is detected by the light receiving element PD3, and the low-level current value is IB controlled completely in a DC manner. |
