| 摘要 |
PURPOSE:To improve the reliability in the detection of a special mark such as a sector mark by using plural pieces of specific patterns forming the constituting pattern of a mask and deciding the detection of the mark in accordance with the threshold logic. CONSTITUTION:The sector mark 1 of a disc is formed of the plural specific constituting patterns 101-105 of the patterns which are not produced by any combination of data, in the form differing from a modulating system for data. The widths of the patterns 101-105 are detected with a binary coding circuit 62, and whether the widths satisfy the condition for the sector mark or not is detected with a circuit 63. The detection signals are outputted in parallel by a paralleling circuit 64. A threshold circuit 65 decides the mark detection according to whether the number of the parallel outputted detection signals is the prescribed threshold value or above and outputs the mark detection signal. With such constitution, the probability at which the detection signal at the point of a normal time is erased on account of an error is decreased, and the probability at which the false signal except the signal at the point of the normal time is generated is decreased, thus reliability in the detection of the special mark is improved. |
