Write clock generation circuit and optical disk apparatus

Abstract

A write clock generation circuit is provided that can detect wobble signal in high accuracy and can appropriately generate write clock with only small jitter even when the operation is switched from reproduction to recording. The wobble signal is obtained by changing stepwise the gain of a variable gain amp in the rear stage of a divided photo detector using a gain control circuit in a predetermined time period just after the beginning of recording. The write clock signal is generated using the above wobble signal. According to this arrangements, the change in wobble signal just before and after the beginning of recording can be reduced, and the gain change of a wobble signal amplitude regulation AGC is made slow. As a result, high frequency deviation of the wobble signal can be reduced even when the operation is switched from reproduction to recording, and the write clock with only small jitter can be generated.

1 - 16 . (canceled)  
   
   
       17 . A wobble signal generation circuit for generating wobble signal based on a wobbling track formed on a recording medium, comprising: 
 two variable gain amps that amplify respective signals from a photo detector divided into two portions by a dividing line corresponding to a tangential direction of the track at a determined gain;    a gain control circuit that determines the gain of said variable gain amps in a particular period immediately after the beginning of data-writing by varying the gain of said variable gain amps stepwise; and    a subtracter that produces wobble signal by subtracting outputs from said respective variable gain amps.    
   
   
       18 . A made-binary wobble signal generation circuit for generating made-binary wobble signal based on a wobbling track formed on a recording medium, comprising: 
 a subtracter that produces wobble signal by subtracting respective signals from a photo detector divided into at least two portions with a dividing line corresponding to a tangential direction of the track;    a variable gain amp that amplifies the wobble signal output from said subtracter at a determined gain;    a gain control circuit that determines the gain of said variable gain amps in a particular period immediately after data-writing has been started by varying the gain of said variable gain amps stepwise;    a wobble amplitude regulation AGC circuit that automatically controls gain thereof so as to regulate amplitude of the wobble signal output from said variable gain amp; and    a making-binary circuit that digitizes signals output from said wobble amplitude regulation AGC circuit into made-binary wobble signal.    
   
   
       19 . A method of generating wobble signal based on a wobbling track formed on a recording medium, the method comprising the steps of: 
 capturing a photo signal;    dividing the captured photo signal into two portions by a dividing line corresponding to a tangential direction of the track;    amplifying the divided signals at a gain varied stepwise in a particular period immediately after the beginning of data-writing; and    subtracting the amplified signals thereby to produce the wobble signal.    
   
   
       20 . A method of generating write clock from wobble signal based on a wobbling track formed on a recording medium, the method comprising the steps of: 
 capturing a photo signal;    dividing the captured photo signal into two portions by a dividing line corresponding to a tangential direction of the track;    amplifying the divided signals at a gain varied stepwise in a particular period immediately after the beginning of data-writing;    subtracting the amplified signals thereby to produce the wobble signal;    regulating amplitude of the produced wobble signal thereby to obtain amplitude-regulated wobble signal;    digitizing the obtained amplitude-regulated wobble signal into made-binary wobble signal; and    generating write clock using the made-binary wobble signal as a reference.    
   
   
       21 . The method as claimed in claim  4 , wherein in the step of amplifying the divided signals, the gain is once reduced to a level lower than a gain level of data-reading in the particular period immediately after the beginning of data-writing, and then increased stepwise to a gain level of data-reading.  
   
   
       22 . A method of generating made-binary wobble signal based on a wobbling track formed on a recording medium, the method comprising the steps of: 
 capturing a photo signal;    dividing the captured photo signal into two portions by a dividing line corresponding to a tangential direction of the track;    subtracting the divided signals;    amplifying the subtracted signals at a gain varied stepwise in a particular period immediately after the beginning of data-writing thereby to produce a wobble signal;    regulating amplitude of the produced wobble signal thereby to obtain amplitude-regulated wobble signal; and    digitizing the obtained amplitude-regulated wobble signal into made-binary wobble signal.    
   
   
       23 . A method of generating write clock from wobble signal based on a wobbling track formed on a recording medium, the method comprising the steps of: 
 capturing a photo signal;    dividing the captured photo signal into two portions by a dividing line corresponding to a tangential direction of the track;    subtracting the divided signals;    amplifying the subtracted signals at a gain varied stepwise in a particular period immediately after the beginning of data-writing thereby to produce a wobble signal;    regulating amplitude of the produced wobble signal thereby to obtain amplitude-regulated wobble signal;    digitizing the obtained amplitude-regulated wobble signal into made-binary wobble signal; and    generating write clock using the made-binary wobble signal as a reference.    
   
   
       24 . The method as claimed in claim  7 , wherein in the step of amplifying the subtracted signals, gain is once reduced to a level lower than a gain level of data-reading in the particular period immediately after the beginning of data-writing, and then increased stepwise to a gain level of data-reading.