| 摘要 |
PROBLEM TO BE SOLVED: To prevent errors and to always receive the stable optical signals regardless of the receiving levels of a photodetector. SOLUTION: A light receiving circuit consists of a photodetector 1 which receives the optical signals and converts them into the electric signals, a preamplifier 2 which amplifies the electric signals, a transistor TR 3 which has its collector connected to a power supply that supplies the power voltage and receives the amplified signals at its base, a resistor 6 which is connected to the emitter of the TR 3 via one of its both ends with the other end grounded, and a variable capacitance means 10 which is connected in parallel to the resistor 6 and has the inter-terminal capacitance that is reduced as the inter-terminal voltage level of the resistor 6 rises. The means 10 can use a variable capacitance diode which is connected in parallel to the resistor 6 with its cathode turned to the emitter. The capacitance of the diode 10 varies when the inter- terminal voltage varies in response to the light receiving level. As result, the signal waveform has no ringing despite a high light receiving level. |
