| 摘要 |
PURPOSE:To perform focus control even in a record erasure section on an optical disk, by biasing a beam position from its original correct track line to left or right in the record erasure section, and increasing the quantity of reflected light. CONSTITUTION:The 1st counter 11 counts a clock signal supplied from a clock source 10 and is used for detecting the erasure section; for example, when it counts clocks corresponding to length Td2, ''1'' is outputted to an AND gate 12. The AND gate 12 sets the 1st flip-flop 13 and then sets the 2nd flip-flop 14 to apply its Q output to an encoder 15 and an AND gate 17. The encoder 15 converts the input into a digital value necessary for generating an offset quantity ros, and a D-A converter 16 converts it into an analog signal, which is impressed as the offset quantity ros to a comparator 7. The 2nd counter 18 is used to detecting a beam spot exiting from the erasure section. |
