Patent ID: 6466533
Filing Date: 2002-10-15
Classification: G11B

Abstract:
A prepit detection unit for reading an optical record medium having an information record track, a guide track, and a prepit including pre-information recorded on the guide track, the prepit detection unit comprising:a light reception element having a first light reception part and a second light reception part divided at least by a division line optically parallel with a tangential direction of the information record track, wherein the first light reception part outputs a first read signal and the second light reception part outputs a second read signal; a potential correction circuit comprising a first correction circuit which produces at least part of a corrected first read signal by adjusting a recorded portion potential of the first read signal to correspond to a first reference potential; and a second correction circuit which produces at least part of a corrected second read signal by adjusting a recorded portion potential of the second read signal to correspond to the first reference potential; a difference circuit that generates a difference signal based on the corrected first read signal and the corrected second read signal, and a prepit detection circuit for detecting the prepit based on the difference signal.