| 摘要 |
PURPOSE:To produce an accurate error signal by producing a tracking error signal from the signal given from a photodetecting area set in parallel to the tangent direction of a pit train and detecting and subtracting an offset voltage component from a level difference obtained in a total reflection mode. CONSTITUTION:The reflected light having a change by the presence or absence of a pit on a disk is received by a photodetector 18. Voltage signals Pa and Pb delivered from photodetecting areas PDa and PDb of the detector 18 are supplied to a tracking error signal producing circuit 24 as well as to an offset voltage detecting circuit 25. The circuit 24 supplies signals Pa and Pb to a subtractor 243 via PHF241a and 241b and absolute value circuit 242a and 242b. The circuit 25 supplies signals Pa and Pb to a substractor 252 via peak holding circuits 251a and 251b. Then output of the subtractor 243 is supplied to a subtractor 26 together with the output of the subtractor 252 obtained via a variable gain device 253. Then an accurate tracking error signal can be supplied to a tracking control circuit 20 from a subtractor 26. |
