Patent ID: 7742373

Claim:
An optical disk drive for scanning an optical disk comprising a substantially circular groove and a land portion separating adjacent parts of said groove, the groove being wobbled, comprising: a beam generator for generating a read beam and directing said read beam to said optical disk, a sensor for sensing a reflected beam produced by said optical disk upon receiving said read beam, and for producing a sensor output signal with a sensor output signal amplitude, an envelope analyzer arranged to: receive said sensor output signal from said sensor, analyze a first envelope of said sensor output signal amplitude, derive a modulation depth M of said first envelope as a variation of said first envelope as a function of time, an indicator for indicating whether said read beam is directed to said groove or to said land portion according to the modulation depth, wherein the modulation depth M is defined as: M=(Emax-Emin)/Emax wherein Emax is the maximum value of the envelope and Emin is the minimum value of the envelope.