| 摘要 |
PROBLEM TO BE SOLVED: To enable a current equivalent to a current which flows into the terminal of a photodiode to be detected at a point, at which a potential can be arbitrarily set by a method wherein a monitor current substantially equal to a photocurrent generated by the photodiode can be detected at the other current output terminal of a current mirror circuit. SOLUTION: A current mirror circuit 100 is composed of a PNP transistor 101 which causes a short circuit between a collector and a base and a PNP transistor 102 substantially equal to the transistor 101 in characteristics. Therefore, the collector potential of the transistor 101 is smaller than a positive power supply potential Vcc just by a voltage across a base and an emitter. The base-emitter voltage of the transistor 102 becomes completely equal to that of the transistor 101, so that a current flowing through the collector of the transistor 102 becomes equal to a current which flows into the cathode of a PD. The collector of the transistor 102 can be utilized as a photocurrent monitoring terminal. |
