Access controlling device for use in an optical disk drive

An optical disk drive, using an optical disk comprising:

• grooves arranged concentrically or spirally;
• a pit section whereon information is predeterminedly recorded by uneven pits having a specified depth;
• and
• a level section whereon grooves and pits do not exist, which is level and interrupts sections of the grooves,
• the optical disk drive comprising:
• rotatively driving means for rotatively driving the optical disk;
• an optical head for converging a light beam as a light spot on the optical disk, the optical disk being driven by the rotatively driving means, and for receiving light reflected from the optical disk and converting it into an electric signal;
• optical head moving means for moving the optical head along radial directions of the optical disk;
• an envelope detecting circuit for detecting an envelope signal, the envelope signal being an envelope of the electric signal, by a time constant circuit which is set to eliminate high-frequency components that appear in the electric signal when the light spot passes the pit section;
• level section detecting means for releasing a level section detecting pulse, the level section detecting pulse showing that the light spot is passing the level section, by detecting a pulse that appears in the envelope signal when the light spot passes the level section, the pulse showing that the light spot is passing the level section;
• time constant switching means for shortening the time constant for the duration of release of the level section detecting pulse;
• a comparator for binarizing the envelope signal and for releasing a binary envelope signal;
• and
• a discrimination circuit for releasing a discrimination signal, the discrimination signal determining whether the light spot is incident on one of the grooves or on an area located between the grooves by using the level section detecting pulse to eliminate a pulse which appears in the binary envelope signal when the light spot passes the level section.