| 摘要 |
PURPOSE:To simplify circuit constitution and to make an accurate decision by using a couple of light emitting elements and photodetecting elements, using two adjacent phototransistors as the photodetecting elements, and inputting output signals to a comparing circuit after applying AGC. CONSTITUTION:Infrared rays from an infrared-ray emission part 3 are reflected by a subject to enter a photodetection part 5. Two phototransistors P-TR1 and P-TR2 are provided adjacently on the focal plane of a condenser lens 51 behind the lens. Photocurrents generated by the phototransistors are inverted and amplified by operational amplifiers OA1 and OA2 and then compared with each other by the comparator CP to decide between two far and close points based upon predetermined 1.2m. Transistors TR2 and TR3 are provided to the bases of the P-TR1 and P-TR2, and the base currents of the P-TR1 and P-TR2 are flowed to the collectors of the TR2 and TR3 to provide negative feedback, holding operation points constant. A capacitor C2 is not capable of being applied with AGC by light emission pulses (1.8kHz) through a resistance R7, capacitor C4, and resistance R17, but is capable of being applied with AGC by a fluorescent lamp (100, 120Hz). |
