| 摘要 |
PURPOSE:To prevent deterioration in waveform when an optical signal with a large amplitude is inputted by inserting a diode being a transistor(TR) whose collector and base are connected together to an emitter circuit of a 1st stage TR of a current voltage conversion amplifier. CONSTITUTION:A current voltage conversion amplifier 2 converting a current signal outputted from a photodetector 1 into a voltage signal is provided with a 1st stage TR 1 whose base connects to an output of the photodetector 1. A diode D2 being a TR whose collector and base are connected together is inserted to an emitter circuit of the 1st stage TR 1 and a base of the diode D2 connects to a constant level (high potential level 4) via a resistor R6. The DC level at the connection point 13 is increased by a voltage drop across the diode d 2 and then the linear region in the voltage drop characteristic at connecting points 11-13 with respect to the input optical current is expanded. Thus, even when the optical signal current with a high amplitude level is inputted, the deterioration in the waveform is avoided. |
