| 摘要 |
PURPOSE:To make an error signal highly accurate, by obtaining the output which is modulated by a frequency which is proportional to the position of a circular image from a light detecting element. CONSTITUTION:Output signals 13 of two light detectors on one axis are inputted to a frequency discriminators 14. When the center of the circular image is shifted by x, discriminated outputs 15 from the corresponding frequency discriminators 14 are supplied to maximum value holding circuits 17. Then holding outputs 18 from the holding circuits 17 are supplied to sample and hold circuits 19 and sampled and held by the output of a delay circuit 20. Then sample and hold outputs 21 having the amplitudes C1 and C2 are obtained from the holding circuit 19. In this way, the variation in the outputs of the optical detectors due to the luminance irregularity of the circular image and the variation in the outputs of the optical detectors due to the change in environment are eliminated and the highly accurate error signal can be always obtained. |
