Method for radial tracking in an optical disc drive

Abstract

A method for radial tracking in an optical disc drive ( 1 ) is described. A DTD tracking error signal (S 3 ) is derived from the wobble-induced signal components (W A , W B , W C , W D ) of the optical detector signal (S R ). This tracking error signal is relatively insensitive to beamlanding errors, and to differences in the signal amplitudes K of the output signal of individual detector segments. Further, the need for a 3-spot grating is eliminated. A distinction is made between on the one hand a situation where the track being followed is empty and on the other hand a situation where the track being followed is written. In case the track being followed is empty, a DTD tracking error signal is derived from the wobble-induced signal components of the optical detector signal, whereas, in case the track being followed is written, a DTD tracking error signal is derived from the data-induced signal components of the optical detector signal.

1 . Method for radial tracking in an optical disc drive ( 1 ), wherein a tracking error signal (S 3 ) is derived from wobble-induced signal components (W A , W B , W C , W D ) of an optical detector output signal (S R ). 
   
   
       2 . Method according to  claim 1 , wherein the tracking error signal (S 3 ) is generated according to the formula
     DTD 4 R =Δ( A,B )+( C,D ), wherein   Δ(A,B) represents the delay τ A −τ B  between signals W A =K A •cos(τ−τ A ) and W B =K B •cos(τ−τ B ),   Δ(C,D) represents the delay τ C −τ D  between signals W C =K C •cos(τ−τ C ) and W D =K D •cos(τ−τ D ), wherein   K A , K B , K C , K D  are respective amplitudes   τ A , τ B , τ C , τ D  are respective phases   τ is the tangential scanning variable   and wherein W A , W B , W C , W D  represent the amount of light received at respective segments of an optical detector ( 35 ).   
   
   
       3 . Method according to  claim 1 , wherein the tracking error signal is generated according to the formula
     DTD 4 T =Δ( A,D )+( C,B ), wherein   Δ(A,D) represents the delay τ A −τ D  between signals W A =K A •cos(τ−τ A ) and W D =K D •cos(τ−τ D ),   Δ(C,B) represents the delay τ C −τ B  between signals W C =K C •cos(τ−τ C ) and W B =K B •cos(τ−τ B ), wherein   K A , K B , K C , K D  are respective amplitudes   τ A , τ B , τ C , τ D  are respective phases   τ is the tangential scanning variable   and wherein W A , W B , W C , W D  represent the amount of light received at respective segments of an optical detector ( 35 ).   
   
   
       4 . Method according to  claim 1 , wherein the tracking error signal is generated according to the formula
     DTD 2=Δ( A+C,B+D ), wherein   Δ(A+C,B+D) represents the delay τ A+C −τ B+D  between signals W A +W C =K A+C •cos(τ−τ A+C ) and W B W D =K B+D •cos(τ−τ B+D ), wherein   K A , K B , K C , K D  are respective amplitudes   τ A , τ B , τ C , τ D  are respective phases   τ is the tangential scanning variable   and wherein W A , W B , W C , W D  represent the amount of light received at respective segments of an optical detector ( 35 ).   
   
   
       5 . Method for radial tracking in an optical disc drive ( 1 ), wherein, if the track being followed is non-written, a tracking error signal (S 3 ) is derived from wobble-induced signal components (W A , W B , W C , W D ) of an optical detector output signal (S R ) in accordance with  claim 1 , and wherein, if the track being followed is written, a tracking error signal (S 3 ) is derived from data-induced signal components of the optical detector output signal (S R ). 
   
   
       6 . Method according to  claim 5 , wherein the optical detector output signal (S R ) is evaluated to determine whether the track being followed is non-written or written. 
   
   
       7 . Method according to  claim 6 , wherein the determination whether the track being followed is non-written or written is made on the basis of the signal power contents of a low-frequency part ( 171 ) of the central aperture signal (CA). 
   
   
       8 . Method according to  claim 7 , wherein the signal power contents of the low-frequency part ( 171 ) of the central aperture signal (CA) is monitored, and wherein, in case a substantial drop in signal power is detected, tracking error signal generation is switched to deriving the tracking error signal from data-induced signal components whereas, in case a substantial rise in signal power is detected, tracking error signal generation is switched to deriving the tracking error signal from wobble-induced signal components (W A , W B , W C , W D ) of an optical detector output signal. 
   
   
       9 . Method according to  claim 6 , wherein the determination whether the track being followed is non-written or written is made on the basis of the signal power contents of a data-frequency part ( 173 ) of the central aperture signal (CA). 
   
   
       10 . Method according to  claim 9 , wherein the signal power contents of the data-frequency part ( 173 ) of the central aperture signal (CA) is monitored, and wherein, in case a substantial rise in signal power is detected, tracking error signal generation is switched to deriving the tracking error signal from data-induced signal components whereas, in case a substantial drop in signal power is detected, tracking error signal generation is switched to deriving the tracking error signal from wobble-induced signal components (W A , W B , W C , W D ) of an optical detector output signal. 
   
   
       11 - 24 . (canceled)