| 摘要 |
PROBLEM TO BE SOLVED: To attain an excellent S/N ratio even when the light receiving circuit is in use at a location where it is exposed under the direct sun light outdoors by employing a series circuit consisting of a 1st light receiving element and of a parallel connection circuit comprising a resistor and a 2nd light emitting element with a larger light receiving area than that of the 1st light receiving element for the light receiving circuit. SOLUTION: A 1st light receiving element 1 has a sufficient response speed to receive a signal light. A 2nd light receiving element 2 connected in series with the 1st light receiving element 1 and in parallel with a resistor has a wider light receiving area than that of the 1st light receiving element and a higher electromotive force when a background light is made incident onto the 2nd light receiving element. Furthermore, a light receiving element whose response speed is slower than the speed of the signal light and that responds insufficiently to the incidence of the signal light is adopted for the 2nd light receiving element 2. In the case that a background light much more intensive than the signal light is made incident, a current in response to the background light is produced even in the 2nd light receiving element 2. Through the constitution above, in the case that the background light is made incident, a reverse bias voltage applied to the 1st light receiving element 1 is increased. |
