| 摘要 |
PURPOSE:To keep a multiplication factor to an optimum value in response to an input signal at all times, by forming a series circuit with an avalanche photo diode and a resistor, and suitably selecting an apply voltage for the circuit and a resistance value of the resistor. CONSTITUTION:An avalanche photo diode APD1 and a resistor 2 are connected in series and a prescribed voltage Vc is applied across the series circuit. An AC component of the voltage drop across the resistor 2 due to an output current i0 of the APD1 is inputted to an amplifier and outputted. A bias voltage of V=Vc-I0R (where; R is a resistance value of the resistor 2) is applied between the anode and the cathode of the APD1, and the current i0 is obtained with the multiplication factor determined with this voltage. The voltage Vc is made equal to a breakdown voltage of the APD1, and I0R is kept sufficiently smaller in comparison with the voltage Vc. Thus, the multiplication factor of the APD1 can always be kept to an optimum value in response to the input signal. |
