| 摘要 |
PURPOSE:To simplify the circuit configuration and to control a reverse bias voltage impressed on an avalanche photo diode(APD) in response to an optical input signal. CONSTITUTION:An optical input signal is converted into an optical current in response to its intensity at an APD1. The current is subject to current-voltage conversion, amplified at a preamplifier 3 and an output signal is obtained. In this case, a voltage drop across a resistor 4 by the optical current is proportional to the optical current. Thus, so long as a voltage of a bias power supply 2 is constant, a reverse bias voltage to the APD1 is changed. That is, when the optical input signal strength is small, the reverse bias voltage to the APD1 is large and when the optical input signal strength is large, the reverse bias voltage to the APD1 is small as automatic variable setting, resulting that the current amplification factor of the APD1 is varied with the optical input signal strength. In other words, the current amplification factor of the APD1 is changed to be an optimum amplification factor in response to the optical input signal strength. |
