| 摘要 |
PROBLEM TO BE SOLVED: To reduce the power consumption of an optical receiving circuit by connecting the gate and drain electrodes of a P-channel FET having its source electrode connected to a power supply to a connection point set between a resistance connected to the power supply via one of its both ends and a light receiving diode and also connecting a capacity connected to a power supply or the ground via one of its both ends to the above connection point. SOLUTION: When a photodetector 1 receives the optical input, a photolelectric current proportional to an input level flows and is converted into voltage by a resistance 3. This voltage secures an averaged optical signal owing to the connection of a capacity 7. The FET 4 and 5 are turned on by the gate voltage change and the power Vcc is supplied to a preamplifier 2 and a next-stage amplifier 6. When the large optical input is supplied to the photodetector 1, the voltage drop of the resistance 3 is increased and it's impossible to secure the bias voltage enough to attain the normal operation of the photodetector 1. Thereby, the drain and gate electrodes of the FET 4 are connected together. When the gate voltage excessively decreases, a current flows to the photodetector 1 from the drain electrode to prevent the lowering of gate voltage. |
