| 摘要 |
PURPOSE:To omit a PLL oscillator for extracting a signal by forming an unevenness pattern at the length of three times or above of one period of the channel clock of the signal recorded at a signal recording area succeeding to the unevenness pattern. CONSTITUTION:A magnetic disk 1, for example, is an optical magnetic disk and rotated and driven at a constant linear velocity. On the disk 1, an emboss area 3 composed of an unevenness pattern and a signal recording area 4 are provided at an equal pitch alternately. At the area 3, the unevenness pattern due to three types 3T, 6T and 9T of the rectangular wave signals is recorded. The signal corresponding to the area 3 detected by a photodetector 12 is sent to a length detecting circuit 18 to detect the length of the unevenness pattern through a comparator 16 and the detecting output is sent to a sub-code processing circuit. Since the unevenness pattern is formed by the length of three times or above of one period T of the channel clock, 3T, 6T and 9T can be detected without a detecting error and a PLL oscillator for extracting the signal of the area 3 can be omitted. |
