| 摘要 |
PURPOSE:To obtain a photodetecting circuit having a sufficient band characteristic and a high receiving sensitivity by connecting respectively in parallel the drains of two electric field effect transistors and the sources and linking a feedback signal from respective drains to respective gates. CONSTITUTION:Two pieces of FET are used, these drains and sources are connected in parallel, between the gate of an FET 2 and the drain, a feedback resistance Rf1 with a large resistance value is connected and between the gate of an FET 3 and the drain, a feedback resistance Rf2 with a small resistance value is connected. Thus, a front end amplifier to fit an APD 1 can be sufficiently made into a wide band. On the other hand, the noise characteristic of the front end amplifier is approximately determined by the feedback resistance Rf1 connected to FET 2. Consequently, since the load resistance of an APD is large, the thermal noise is decreased and a wide band photodetecting circuit having a high receiving sensitivity can be realized. |
