| 摘要 |
PURPOSE:To make it possible to obtain high-speed amplitude limiting action by inserting a transistor between the output terminals of a photoelectric conversion circuit to be connected with them while using a common collector and base terminal. CONSTITUTION:An npn transistor Tr has a common base and collector terminal and is connected to output terminals O1, O2 while being connected in series with a DC voltage source E. When a laser beam impinges on an APD, a photomultiplying current flows through the APD, the resistance value decreases, and output voltages are generated at both ends of a resistor R2, and when the laser beam impinging on the APD is eliminated, the photomultiplying current flowing in the APD is eliminated, the resistance value rises and the output voltage at both ends of the resistor R2 are lowered. When the level of the laser beam becomes excessive and the output voltage between the terminals O1, O2 becomes excessive, the transistor Tr starts to conduct and its output voltage is lowered to a value obtained by addition of the voltage of the voltage source E to the voltage between collector and emitter, so that amplitude limiting action is performed at a very high speed. Therefore, the discharge time for a small number of carriers is reduced to as small as not less than one tenth multiplied by a number less than ten and the response speed is increased ten to less than hundred times. |
