| 摘要 |
PURPOSE:To enable exact detection of an original size by driving with pulse and time dividely light emitting elements, detecting the outputs from photodetectors according to the time divisions and eliminating the influence of crosstalk light. CONSTITUTION:Timing signals 11a, 11b are inputted to driving circuits 14a, 14b for light emitting elements which drive alternately light emitting elements 51, 53, 55 and 52, 54. More specifically, the adjacent elements 52, 54 are put out while the elements 51, 53, 55 emit light. Photodetector 61-65 sides are connected respectively with amplifier circuits 151-155, etc. to amplify the light outputs from the respective photodetectors 6 and at the same time said outputs are compared with reference values and the results thereof are taken into a latch circuit 17. The closure of an original cover 2 is confirmed by a decision circuit 21 which decides an original size. The S/N ratio by the crosstalk light of the other light emitting elements is thus only the crosstalk positioned in every other element, by which the influence of the crosstalk light is eliminated. The exact detection of the original size is thus made possible. |
